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The Life and Death of the Dinosaurs _ Science for Sleep · Night Science Stories

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  Speaker 1: Good evening, and welcome to the Sleepy Scientist. I'm very
• 0:03
  Speaker 1: glad you've joined me. Before we head back into a
• 0:06
  Speaker 1: world that vanished millions of years ago, I'm always interested
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  Speaker 1: to know where these quiet evenings find you. So if
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  Speaker 1: you feel like sharing, let me know in the comments
• 0:16
  Speaker 1: where in the world you're listening from. Perhaps you're already
• 0:19
  Speaker 1: tucked into bed, perhaps you're on a slow journey home,
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  Speaker 1: or maybe you're simply enjoying a little peace after a
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  Speaker 1: long day. Wherever you are, I hope you're comfortable, settled
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  Speaker 1: and ready to let everything else become a little less
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  Speaker 1: important for a while. If you prefer listening without the
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  Speaker 1: glow of a screen, The Sleepy Scientist is also on Spotify,
• 0:41
  Speaker 1: with a link waiting in the description, so whenever you're ready,
• 0:44
  Speaker 1: you can close your eyes, get comfortable and just listen.
• 0:48
  Speaker 1: I'll keep wandering through the story either way, and if
• 0:52
  Speaker 1: these long, gentle journeys through science help you relax, A
• 0:55
  Speaker 1: like and a subscribe are always appreciated. They're a small
• 0:59
  Speaker 1: way of keeping these quiet evenings going and of letting
• 1:02
  Speaker 1: them find their way to anyone else who might need them.
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  Speaker 1: And if you've been listening for a while already, thank you.
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  Speaker 1: It genuinely means a great deal to have you here.
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  Speaker 1: Tonight I'll try not to make dinosaurs quite so interesting
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  Speaker 1: that they keep you awake. Although that may be difficult,
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  Speaker 1: we're going to travel back more than 200 million years
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  Speaker 1: through forests filled with giants, predators, feathers, eggs and migrations,
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  Speaker 1: all the way to one of the most fateful days
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  Speaker 1: in the history of life on Earth. So even if
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  Speaker 1: sleep arrives somewhere along the way, at least you may
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  Speaker 1: drift off knowing how an entire age of the planet rose,
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  Speaker 1: flourished and almost disappeared. How did the dinosaurs come to
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  Speaker 1: rule the Earth for more than 160 million years, and
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  Speaker 1: what finally brought their world to an end? Shall we begin?
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  Speaker 1: Around 252 million years ago, Long before the first true
• 1:57
  Speaker 1: dinosaur walked across the Earth, life experienced a catastrophe so
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  Speaker 1: severe that almost everything afterwards would be shaped by it.
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  Speaker 1: This was the Permian-Triassic mass extinction, the largest known mass
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  Speaker 1: extinction in the history of our planet. The precise details
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  Speaker 1: are still studied, but the broad picture is clear. Enormous
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  Speaker 1: volcanic eruptions in what is now Siberia released vast quantities
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  Speaker 1: of gases into the atmosphere. Climate changed dramatically. Oceans warmed,
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  Speaker 1: oxygen levels fell, and marine chemistry was disrupted. On land,
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  Speaker 1: ecosystems were transformed as well. By the time the crisis
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  Speaker 1: had passed, the majority of species that had existed during
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  Speaker 1: the Permian period were gone. The world did recover, but
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  Speaker 1: recovery did not mean simply rebuilding what had been there before. Instead,
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  Speaker 1: Evolution began filling the empty spaces with something new. The
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  Speaker 1: early Triassic Earth would have looked profoundly unfamiliar. Almost all
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  Speaker 1: of the planet's land was joined together into one enormous
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  Speaker 1: supercontinent called Pangaea. It stretched across an extraordinary range of latitudes,
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  Speaker 1: surrounded by a global ocean, and much of its interior
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  Speaker 1: lay a very long way from the moderating influence of
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  Speaker 1: the sea. That geography helped create strong climatic extremes. Large
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  Speaker 1: parts of the continental interior were hot and dry. Rainfall
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  Speaker 1: could be highly seasonal. Deserts and semi-arid landscapes covered immense areas,
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  Speaker 1: although wetter environments existed around coastlines, rivers and some higher latitudes.
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  Speaker 1: There were no flowering plants, no grasslands and certainly no
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  Speaker 1: familiar forests filled with songbirds and mammals. Even the animals
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  Speaker 1: wandering through these landscapes belonged to a world that had
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  Speaker 1: not yet invented anything quite like the ecosystems we know today.
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  Speaker 1: Among the groups beginning to flourish were the archosaurs. Archosaurs
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  Speaker 1: are an enormously important branch of reptiles. Their descendants and
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  Speaker 1: relatives would eventually include crocodilians, pterosaurs and dinosaurs, although those
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  Speaker 1: three groups should not be confused with one another. A
• 4:13
  Speaker 1: pterosaur flying above a dinosaur was not itself a dinosaur.
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  Speaker 1: A crocodilian relative sharing a riverbank with one was not
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  Speaker 1: a dinosaur either. They were different branches of a much
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  Speaker 1: larger family tree. In the aftermath of the Permian-Triassic extinction,
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  Speaker 1: archosaurs underwent what biologists call an evolutionary radiation. This happens
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  Speaker 1: when a lineage diversifies into many forms, often as organisms
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  Speaker 1: exploit newly available ecological opportunities, and there were plenty of
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  Speaker 1: opportunities available. with so many. Earlier species gone, terrestrial ecosystems
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  Speaker 1: contained ecological niches waiting to be occupied. Different archosaur groups
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  Speaker 1: experimented in the slow and unguided way evolution always does,
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  Speaker 1: with different body shapes, methods of movement and ways of
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  Speaker 1: finding food. Some were predators, others were herbivores, some moved
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  Speaker 1: on four legs while others increasingly relied on two. For
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  Speaker 1: much of the Triassic, There was no obvious reason to
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  Speaker 1: assume that dinosaurs would eventually become the most famous of
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  Speaker 1: them all. In fact, the earliest ancestors of dinosaurs were
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  Speaker 1: surrounded by successful competitors. Crocodile-line archosaurs included animals far more
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  Speaker 1: diverse than modern crocodiles might suggest. Some were heavily armoured.
• 5:34
  Speaker 1: Some were large predators. Others occupied herbivorous roles that would
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  Speaker 1: later become strongly associated with dinosaurs. The evolutionary tree of
• 5:43
  Speaker 1: archosaurs are divided into two particularly important branches. One was
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  Speaker 1: the crocodile-line archosaurs, formerly known as Pseudosuchians. Modern crocodilians are
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  Speaker 1: the surviving members of this side of the family. The
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  Speaker 1: other was the bird-line archosaurs, known as Avomete tarsalians. It
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  Speaker 1: was somewhere on this second branch that dinosaurs eventually emerged,
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  Speaker 1: and rather wonderfully, that bird-line name hints at where the
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  Speaker 1: story ultimately leads. Modern birds are not merely animals that
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  Speaker 1: appeared after the dinosaurs, they belong within the dinosaur lineage itself.
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  Speaker 1: So the branch that would one day produce the first
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  Speaker 1: dinosaurs would also, much later, produce sparrows, owls, penguins and
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  Speaker 1: every other living bird. But none of that was obvious yet.
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  Speaker 1: During the Triassic, subtle changes in anatomy were beginning to
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  Speaker 1: distinguish dinosaur ancestors from many of the reptiles around them.
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  Speaker 1: One of the most important involved the legs. Many reptiles
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  Speaker 1: hold their limbs partly out to the sides of the body,
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  Speaker 1: producing a sprawling stance. Early dinosaurs and their closest relatives
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  Speaker 1: increasingly carried their limbs more directly underneath themselves. The hip joint,
• 6:54
  Speaker 1: thigh bone and pelvis became arranged in ways that allowed
• 6:57
  Speaker 1: the body to be supported from below. This was not
• 7:01
  Speaker 1: simply a cosmetic difference. An upright posture could provide more
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  Speaker 1: efficient support and locomotion, especially for animals moving actively across land.
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  Speaker 1: The hind limbs of early dinosaur-line animals became increasingly specialised,
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  Speaker 1: and many early dinosaurs would eventually become accomplished bipeds, balancing
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  Speaker 1: their bodies over powerful back legs while using the tail
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  Speaker 1: as a counterweight. Their ankles, hips and vertebrae also developed
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  Speaker 1: combinations of features that paleontologists can use to distinguish true
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  Speaker 1: dinosaurs from their close relatives. No single feature suddenly announced
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  Speaker 1: that a dinosaur had arrived. Evolution does not normally work
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  Speaker 1: with such tidy boundaries. Instead, populations accumulate changes generation after generation.
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  Speaker 1: Over millions of years, one branch gradually becomes different enough
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  Speaker 1: from its relatives that scientists looking backwards through the fossil
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  Speaker 1: record recognise a new group. That makes the precise beginning
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  Speaker 1: of dinosaurs surprisingly difficult to identify. There are fossils from
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  Speaker 1: the Triassic that may represent extremely early dinosaurs, while others
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  Speaker 1: seem to belong to animals standing just outside Dinosauria on
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  Speaker 1: the evolutionary tree. The distinction can depend upon small details
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  Speaker 1: preserved in fragmentary bones. What is clear is that dinosaurs
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  Speaker 1: began modestly. There was no first morning when enormous long-necked
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  Speaker 1: giants appeared over the horizon, followed conveniently by a Tyrannosaurus
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  Speaker 1: for dramatic effect. The earliest members of the dinosaur lineage
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  Speaker 1: were generally much smaller animals living among a crowded assortment
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  Speaker 1: of other reptiles. They were not rulers of the world.
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  Speaker 1: Not yet. They were simply one branch among many, evolving
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  Speaker 1: on a planet still recovering from the greatest biological catastrophe
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  Speaker 1: it had experienced. And slowly, among the dry landscapes, seasonal
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  Speaker 1: rivers and recovering ecosystems of the Triassic, animals with increasingly
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  Speaker 1: recognisable dinosaur anatomy began to appear. From those comparatively unremarkable
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  Speaker 1: beginnings would come one of the longest and most extraordinary
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  Speaker 1: periods of terrestrial dominance in the history of life. For
• 9:13
  Speaker 1: more than 160 million years, dinosaurs would continue to change,
• 9:18
  Speaker 1: diversify and spread across the planet. But their story began quietly,
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  Speaker 1: in the shadow of extinction. By the middle and late Triassic,
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  Speaker 1: the first true dinosaurs were beginning to appear. But identifying
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  Speaker 1: the exact moment when dinosaurs began is not as simple
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  Speaker 1: as finding one fossil and drawing a line beneath it.
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  Speaker 1: The earliest part of their history is incomplete. Fossils are rare,
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  Speaker 1: rock layers are unevenly preserved, and the animals closest to
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  Speaker 1: the origin of dinosaurs often differ from one another only
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  Speaker 1: in subtle anatomical details. Evolution, of course, does not produce
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  Speaker 1: neat labels. There was no single generation in which an
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  Speaker 1: animal suddenly became unmistakably dinosaurian in every possible sense. The
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  Speaker 1: transition happened gradually, through small changes accumulated over long spans
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  Speaker 1: of time. That is why the oldest possible dinosaur remains
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  Speaker 1: are still debated. One intriguing example is Neasosaurus. known from
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  Speaker 1: fossils discovered in what is now Tanzania. These remains are
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  Speaker 1: roughly 240 million years old, placing the animal in the
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  Speaker 1: Middle Triassic and potentially making it older than the earliest
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  Speaker 1: universally accepted dinosaurs by around 10 million years. Neasosaurus is
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  Speaker 1: known from only limited material, including parts of the vertebral
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  Speaker 1: column and limb bones, so there is a great deal
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  Speaker 1: that scientists cannot say with confidence. Some features appear dinosaur-like,
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  Speaker 1: especially aspects of the upper arm bone and vertebrae. But
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  Speaker 1: because the fossil is incomplete, paleontologists remain cautious. Neasosaurus may
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  Speaker 1: have been a very early dinosaur, or it may have
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  Speaker 1: belonged to an extremely close relative living just outside Dinosauria.
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  Speaker 1: That uncertainty is important. It is not a weakness in
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  Speaker 1: paleontology so much as an honest reflection of what the
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  Speaker 1: evidence allows. Sometimes the fossil record provides a nearly complete skeleton.
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  Speaker 1: Sometimes it provides several bones and a rather large question mark.
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  Speaker 1: Much firmer evidence appears a little later. Around 230 million
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  Speaker 1: years ago, in what is now northwestern Argentina, an ecosystem
• 11:36
  Speaker 1: preserved in the Eschigualasto formation contained animals that can be
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  Speaker 1: recognised much more confidently as early dinosaurs. among the best
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  Speaker 1: known is Eoraptor. Eoraptor was a small, lightly built animal,
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  Speaker 1: only around a metre or so in length. It walked
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  Speaker 1: mainly on two legs, and had grasping hands, a long tail,
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  Speaker 1: and a relatively delicate skull. Its teeth suggest a varied diet,
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  Speaker 1: and paleontologists have debated exactly where it belongs within the
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  Speaker 1: earliest dinosaur family tree. Even so, it gives us a
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  Speaker 1: valuable glimpse of what the first dinosaurs looked like. Another
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  Speaker 1: early form from the same broad region is Herrerasaurus. Herrerasaurus
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  Speaker 1: was considerably larger, reaching several metres in length, and was
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  Speaker 1: clearly adapted for a predatory lifestyle. It had powerful hind limbs,
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  Speaker 1: grasping hands and sharp teeth. Its anatomy is primitive compared
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  Speaker 1: with later theropods, and its exact placement on the dinosaur
• 12:37
  Speaker 1: family tree has also been debated, but it is unmistakably
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  Speaker 1: part of the early dinosaur story. These animals would have
• 12:45
  Speaker 1: looked rather different from the dinosaurs that usually dominate books,
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  Speaker 1: films and museum halls. There were no enormous long-necked sauropods yet.
• 12:54
  Speaker 1: There were no horned ceratopsians, no giant tyrannosaurs. The earliest
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  Speaker 1: definitive dinosaurs were generally small to medium-sized, lightly constructed and
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  Speaker 1: often bipedal. Many would have moved quickly across the ground.
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  Speaker 1: their bodies balanced over powerful hind limbs and their long
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  Speaker 1: tails extending behind them. That body plan was one of
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  Speaker 1: the clues paleontologists used to distinguish true dinosaurs from other
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  Speaker 1: Triassic archosaurs. The process is far more precise than simply
• 13:25
  Speaker 1: looking at an animal and deciding that it appears dinosaur-like.
• 13:30
  Speaker 1: Scientists examine the structure of the pelvis, the shape of
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  Speaker 1: the hip socket, the connection between the femur and the pelvis.
• 13:38
  Speaker 1: the arrangement of the ankle, details of the vertebrae and
• 13:42
  Speaker 1: features of the limbs. One especially important characteristic is the
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  Speaker 1: open hip socket found in dinosaurs. In many other reptiles,
• 13:51
  Speaker 1: the socket where the head of the femur meets the
• 13:53
  Speaker 1: pelvis is backed by solid bone. In dinosaurs, the arrangement
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  Speaker 1: is more open, helping support a limb posture in which
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  Speaker 1: the legs are held directly beneath the body. The head
• 14:05
  Speaker 1: of the femur also projects inward toward the hip. helping
• 14:08
  Speaker 1: create the upright stance that became such a fundamental part
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  Speaker 1: of dinosaur locomotion. These details may sound small, but in paleocentology,
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  Speaker 1: small details can carry enormous evolutionary meaning. A ridge on
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  Speaker 1: a bone, the shape of a joint, or the position
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  Speaker 1: of a muscle attachment can reveal how an extinct animal
• 14:29
  Speaker 1: moved and where it belongs. Within the tree of life,
• 14:33
  Speaker 1: the word dinosaur itself came much later. In 1842, the
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  Speaker 1: British anatomist Sir Richard Owen introduced the name Dinosauria. He
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  Speaker 1: based the group on several large fossil reptiles then known
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  Speaker 1: from Britain, including Megalosaurus, Iguanodon and Hyliosaurus. The name is
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  Speaker 1: often loosely translated as something like terrible lizards, although Owen
• 14:55
  Speaker 1: was not simply trying to describe frightening animals. He recognised
• 15:00
  Speaker 1: that these fossils shared anatomical features that separated them from
• 15:03
  Speaker 1: other reptiles known at the time. Our understanding of dinosauria
• 15:07
  Speaker 1: has changed enormously since Owen's day. Modern paleontologists define dinosaurs
• 15:13
  Speaker 1: through evolutionary relationships rather than simply by size, age or
• 15:18
  Speaker 1: general appearance. As a result, many creatures commonly grouped with
• 15:22
  Speaker 1: dinosaurs in popular culture are not dinosaurs at all. Demetrodon,
• 15:26
  Speaker 1: for example, is frequently placed beside dinosaurs in toys and illustrations.
• 15:32
  Speaker 1: usually because it looks suitably prehistoric and has a large
• 15:35
  Speaker 1: sail on its back. But Demetrodon lived tens of millions
• 15:38
  Speaker 1: of years before the first dinosaurs appeared and belonged to
• 15:42
  Speaker 1: the Synapsid lineage, the same broad evolutionary branch that eventually
• 15:46
  Speaker 1: produced mammals. Marine reptiles such as plesiosaurs and mosasaurs were
• 15:51
  Speaker 1: not dinosaurs either, nor were pterosaurs, despite the fact that
• 15:55
  Speaker 1: they flew above dinosaur ecosystems and were close archosaur relatives.
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  Speaker 1: Dinosauria is a specific evolutionary group, not a convenient basket
• 16:05
  Speaker 1: for anything large, reptilian and extinct. And even once dinosaurs
• 16:09
  Speaker 1: had clearly appeared, they did not immediately take over. In
• 16:14
  Speaker 1: late Triassic ecosystems, they remained only part of a much
• 16:17
  Speaker 1: larger community. Crocodile-line archosaurs were still diverse and successful. Other
• 16:23
  Speaker 1: reptile groups occupied important herbivorous and predatory roles. Dinosaurs were present,
• 16:29
  Speaker 1: but they were not yet the dominant large animals across
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  Speaker 1: the landscape. That would come later. For now, the first
• 16:36
  Speaker 1: true dinosaurs were still relatively modest animals, moving through ecosystems
• 16:41
  Speaker 1: crowded with competitors. There is something rather fitting about that beginning.
• 16:47
  Speaker 1: One of the most successful groups of land animals in
• 16:50
  Speaker 1: Earth's history did not arrive with fanfare. It emerged quietly,
• 16:55
  Speaker 1: gradually and somewhat ambiguously. in a world where there was
• 16:59
  Speaker 1: no obvious reason to expect that these small bipedal creatures
• 17:02
  Speaker 1: would eventually produce giants. But the basic dinosaur body plan
• 17:07
  Speaker 1: was now in place. And once it existed, evolution had
• 17:11
  Speaker 1: more than 160 million years to experiment with it. Once
• 17:16
  Speaker 1: the first true dinosaurs had appeared, their evolution did not
• 17:20
  Speaker 1: follow a single path. Instead, the dinosaur family tree began
• 17:24
  Speaker 1: to divide. This is one of the most important ideas
• 17:28
  Speaker 1: in understanding their history, because the dinosaurs that would later
• 17:31
  Speaker 1: become familiar to us did not emerge fully formed. Tyrannosaurus
• 17:36
  Speaker 1: did not simply appear as a giant predator. Triceratops did
• 17:40
  Speaker 1: not arrive already carrying its enormous horns and frill. The
• 17:44
  Speaker 1: great long-necked sauropods were not born as giants. All of
• 17:48
  Speaker 1: these forms were produced gradually, through branching evolutionary lineages that
• 17:53
  Speaker 1: changed over immense spans of time. Among the earliest dinosaurs,
• 17:58
  Speaker 1: several major groups began to separate from one another. These
• 18:01
  Speaker 1: branches would eventually produce an extraordinary range of animals, from
• 18:06
  Speaker 1: tiny feathered hunters to gigantic plant-eaters weighing many tens of tonnes.
• 18:12
  Speaker 1: One of the most important of these branches was Theropoda.
• 18:16
  Speaker 1: Theropods were predominantly bipedal dinosaurs, meaning that they usually moved
• 18:21
  Speaker 1: on two legs. Their hind limbs were often powerful. Their
• 18:25
  Speaker 1: bodies were balanced by long tails, and many early forms
• 18:28
  Speaker 1: were active predators. Over time, theropods diversified enormously. Some remained
• 18:35
  Speaker 1: relatively small. Others became enormous. Eventually, the lineage produced predators
• 18:41
  Speaker 1: such as Allosaurus, Spinosaurus and Tyrannosaurus, animals that occupied some
• 18:46
  Speaker 1: of the highest positions in their respective food webs. But
• 18:49
  Speaker 1: this same branch also gave rise to something much smaller,
• 18:53
  Speaker 1: and in evolutionary terms, far more enduring. Birds. Modern birds
• 19:00
  Speaker 1: evolved from small feathered theropod dinosaurs, which means that every
• 19:04
  Speaker 1: living bird belongs within the theropod branch of the dinosaur
• 19:07
  Speaker 1: family tree. The contrast is remarkable. A hummingbird and Tyrannosaurus
• 19:13
  Speaker 1: belong to the same broad dinosaur lineage, although separated by
• 19:17
  Speaker 1: a vast amount of evolutionary change. Another major branch was
• 19:21
  Speaker 1: formed by the sauropodomorphs, the earliest? Sauropodomorphs were nothing like
• 19:27
  Speaker 1: the gigantic long-necked animals that would later dominate many Jurassic landscapes.
• 19:33
  Speaker 1: Many Triassic representatives were comparatively modest in size. Some walked
• 19:38
  Speaker 1: mainly on two legs, while others increasingly relied on four.
• 19:42
  Speaker 1: Their necks were beginning to lengthen, their bodies were becoming
• 19:45
  Speaker 1: more heavily built, and their feeding adaptations were moving them
• 19:49
  Speaker 1: toward a predominantly herbivorous lifestyle. Across millions of years, this
• 19:54
  Speaker 1: lineage eventually produced the sauropods. These were the enormous long-necked
• 19:58
  Speaker 1: dinosaurs that included forms such as Diplodocus, Brachiosaurus, and many
• 20:04
  Speaker 1: later Titanosaurs. Some would grow longer than a large passenger
• 20:08
  Speaker 1: aircraft and weigh many tens of tonnes. But the giant
• 20:12
  Speaker 1: sauropod body plan was not an instant invention. It was
• 20:15
  Speaker 1: the result of countless smaller evolutionary changes involving the skeleton,
• 20:20
  Speaker 1: respiratory system, feeding strategy, growth rate, posture and body proportions.
• 20:27
  Speaker 1: A third enormous radiation produced the Ornithischian dinosaurs. Ornithischians were
• 20:32
  Speaker 1: almost entirely herbivorous, and would eventually include many of the
• 20:36
  Speaker 1: most visually distinctive dinosaurs ever to evolve. Stegosaurs developed rows
• 20:41
  Speaker 1: of plates along their backs and formidable spikes on their tails.
• 20:46
  Speaker 1: Ankylosaurs became heavily armoured, with some species carrying massive bony
• 20:50
  Speaker 1: clubs at the ends of their tails. Ornithopods evolved into
• 20:54
  Speaker 1: extremely successful herbivores, eventually including the large hadrosaurs, sometimes called
• 21:00
  Speaker 1: duck-billed dinosaurs. Ceratoptions produced animals such as Triceratops, with enormous skulls,
• 21:08
  Speaker 1: horns and broad neck frills. These groups looked so different
• 21:13
  Speaker 1: from one another that it can be easy to forget
• 21:15
  Speaker 1: that they all descended from much simpler ancestral forms. Traditionally,
• 21:20
  Speaker 1: paleontologists divided dinosaurs into two enormous groups called Saurischia and Ornithischia.
• 21:27
  Speaker 1: The names refer primarily to differences in the arrangement of
• 21:30
  Speaker 1: bones within the pelvis. Saurischia has historically included theropods and sauropodomorphs.
• 21:37
  Speaker 1: Ornithischia included the diverse plant-eating groups such as stegosaurs, ankylosaurs,
• 21:43
  Speaker 1: ornithopods and ceratopsians. For well over a century, this arrangement
• 21:48
  Speaker 1: formed the standard framework for understanding the deepest branches of
• 21:52
  Speaker 1: dinosaur evolution. But science does not remain fixed simply because
• 21:56
  Speaker 1: an idea has been familiar for a long time. More
• 21:59
  Speaker 1: recent studies have questioned exactly how the earliest branches of
• 22:03
  Speaker 1: the dinosaur family tree should be arranged. Some analyses have
• 22:07
  Speaker 1: suggested alternative relationships, placing certain groups together in ways that
• 22:12
  Speaker 1: differ from the traditional model. The details remain debated. This
• 22:16
  Speaker 1: does not mean paleontologists suddenly have no idea how dinosaurs
• 22:20
  Speaker 1: are related. The broad evolutionary relationships among many later dinosaur
• 22:25
  Speaker 1: groups are well supported. The uncertainty lies mainly near the
• 22:29
  Speaker 1: deepest roots of the tree, where the earliest dinosaurs were
• 22:33
  Speaker 1: still quite similar to one another and the fossil record
• 22:36
  Speaker 1: is incomplete. That is a common problem in evolutionary science.
• 22:41
  Speaker 1: The closer we move toward the origin of a major group,
• 22:44
  Speaker 1: the smaller the anatomical differences may become between neighbouring branches.
• 22:49
  Speaker 1: What matters most is that dinosaur evolution was always branching.
• 22:54
  Speaker 1: There was no ladder leading from simple dinosaurs towards supposedly
• 22:58
  Speaker 1: advanced ones. Evolution does not have a destination. A small
• 23:03
  Speaker 1: Triassic dinosaur was not an unfinished version of Tyrannosaurus. It
• 23:08
  Speaker 1: was a successful organism adapted to its own environment. Later
• 23:12
  Speaker 1: dinosaurs became different because populations accumulated different changes while facing
• 23:18
  Speaker 1: different ecological pressures. As dinosaurs spread across changing landscapes, These
• 23:24
  Speaker 1: branches became increasingly specialised. Skulls changed. Some became deep and
• 23:30
  Speaker 1: powerful for biting flesh. Others developed broad surfaces, beaks or
• 23:36
  Speaker 1: elaborate batteries of grinding teeth for processing plants. Limbs changed
• 23:41
  Speaker 1: as well. Some dinosaurs became faster runners. Others evolved massive
• 23:46
  Speaker 1: column-like legs capable of supporting enormous bodies. Some reduced their forelimbs,
• 23:52
  Speaker 1: while others transformed them into wings. Necks could become extraordinarily long.
• 23:57
  Speaker 1: Tails could act as counterbalances, defensive weapons or supports for
• 24:01
  Speaker 1: complex display structures. Armour appeared in the skin and skeleton
• 24:06
  Speaker 1: of some herbivores. Horns and crests evolved. Feathers became increasingly
• 24:11
  Speaker 1: elaborate in many theropods. The relatively compact and lightly built
• 24:16
  Speaker 1: dinosaurs of the Triassic were. Therefore only the beginnings. Their
• 24:21
  Speaker 1: descendants gradually explored an extraordinary range of ecological possibilities, and
• 24:26
  Speaker 1: none of these later forms appeared independently from nowhere. Every
• 24:31
  Speaker 1: specialised tooth, every elongated neck, every armoured plate and every
• 24:36
  Speaker 1: feather was connected to something that existed before it. Evolution
• 24:41
  Speaker 1: worked through inheritance. Each generation began with a body plan
• 24:46
  Speaker 1: inherited from its ancestors, then passed on slightly altered versions
• 24:50
  Speaker 1: of that plan. Over enough time, those accumulated changes could
• 24:55
  Speaker 1: produce animals that looked almost unimaginably different from the creatures
• 25:00
  Speaker 1: at the base of the family tree. That is why
• 25:02
  Speaker 1: the history of dinosaurs is best imagined not as a
• 25:05
  Speaker 1: straight road, but as an enormous spreading tree. Branches divided,
• 25:11
  Speaker 1: some flourished, others ended. New branches appeared within old ones,
• 25:16
  Speaker 1: and each explored a slightly different way of surviving. From
• 25:20
  Speaker 1: those early divisions would eventually come nearly every dinosaur shape
• 25:24
  Speaker 1: we recognise today. The giants, the predators, the armoured herbivores
• 25:30
  Speaker 1: and the feathered forms were all variations on a shared
• 25:34
  Speaker 1: evolutionary inheritance, shaped slowly across millions upon millions of years.
• 25:40
  Speaker 1: By around 201 million years ago, The Triassic world had
• 25:45
  Speaker 1: already changed enormously from the one in which the first
• 25:49
  Speaker 1: dinosaurs appeared. Dinosaurs had diversified, but they were still sharing
• 25:54
  Speaker 1: the land with many other successful groups of reptiles. Some
• 25:59
  Speaker 1: of their most formidable competitors belonged to the crocodile line archosaurs,
• 26:04
  Speaker 1: which had evolved into an extraordinary variety of forms. There
• 26:08
  Speaker 1: were large predators, heavily armoured herbivores, and animals occupying ecological
• 26:14
  Speaker 1: roles that dinosaurs would later come to dominate. Then the
• 26:18
  Speaker 1: planet entered another period of profound disruption. The Antriassic mass
• 26:23
  Speaker 1: extinction was one of the five largest mass extinctions recognised
• 26:27
  Speaker 1: in the fossil record. It affected life in the oceans
• 26:30
  Speaker 1: as well as on land, eliminating many groups and reorganising
• 26:34
  Speaker 1: ecosystems on a global scale. The leading explanation for this
• 26:39
  Speaker 1: crisis involves an immense episode of volcanic activity known as
• 26:43
  Speaker 1: the Central Atlantic Magmatic Province. At the time, the supercontinent
• 26:49
  Speaker 1: Pangea was beginning to fracture. North America, South America, Africa
• 26:54
  Speaker 1: and Europe were slowly being pulled apart as tectonic forces
• 26:58
  Speaker 1: stretched and split the crust. Along those enormous fractures, magma
• 27:03
  Speaker 1: rose from deep within the Earth. The resulting volcanic province
• 27:07
  Speaker 1: was immense. Lava erupted across regions that now separated by
• 27:12
  Speaker 1: the Atlantic Ocean, leaving related volcanic rocks in eastern North America,
• 27:17
  Speaker 1: northern South America, western Africa and parts of Europe. But
• 27:23
  Speaker 1: the environmental danger was not simply that lava covered the landscape.
• 27:28
  Speaker 1: The much greater problem came from what the eruptions released
• 27:30
  Speaker 1: into the atmosphere. Vast quantities of carbon dioxide entered the air.
• 27:36
  Speaker 1: Carbon dioxide is a greenhouse gas, and increasing its concentration
• 27:41
  Speaker 1: can trap more heat within the climate system. Over time,
• 27:45
  Speaker 1: this could drive substantial global warming. At the same time,
• 27:49
  Speaker 1: sulphur-bearing gases could produce aerosols high in the atmosphere. These
• 27:54
  Speaker 1: tiny particles can reflect sunlight away from the Earth, causing
• 27:58
  Speaker 1: shorter periods of cooling. The result was not a simple
• 28:02
  Speaker 1: movement toward one stable temperature. Instead, ecosystems may have been
• 28:07
  Speaker 1: subjected to repeated climatic shocks, with rapid changes occurring against
• 28:12
  Speaker 1: a broader background of warming. The oceans suffered as well.
• 28:17
  Speaker 1: As atmospheric carbon dioxide increased, more of it dissolved into seawater.
• 28:23
  Speaker 1: This altered ocean chemistry and contributed to ocean acidification, placing
• 28:28
  Speaker 1: additional stress on marine organisms and particularly those that relied
• 28:32
  Speaker 1: on calcium carbonate to build shells or skeletons. Warming water
• 28:38
  Speaker 1: can also hold less dissolved oxygen, creating further difficulties for
• 28:42
  Speaker 1: marine life. On land, rapid climatic shifts changed rainfall, vegetation
• 28:48
  Speaker 1: and habitats. Organisms adapted to particular environmental conditions suddenly found
• 28:54
  Speaker 1: themselves living on a planet that was becoming less predictable.
• 28:58
  Speaker 1: Many species disappeared. Among the losses were several groups of
• 29:02
  Speaker 1: archosaurs that had spent much of the Triassic living alongside
• 29:05
  Speaker 1: the earliest dinosaurs. This is important because the rise of
• 29:09
  Speaker 1: dinosaurs is sometimes imagined as a straightforward competition in which
• 29:13
  Speaker 1: dinosaurs simply proved themselves stronger, faster or somehow better than
• 29:19
  Speaker 1: everything around them. The fossil record tells a more complicated story.
• 29:25
  Speaker 1: Dinosaurs did not necessarily conquer every rival through direct competition.
• 29:30
  Speaker 1: Many of those rivals disappeared during a mass extinction. Dinosaurs survived.
• 29:36
  Speaker 1: So did pterosaurs, which would continue to dominate many aerial ecosystems,
• 29:41
  Speaker 1: and several crocodile-line archosaurs that ultimately produced the ancestors of
• 29:47
  Speaker 1: modern crocodilians. Exactly why dinosaurs survived the crisis more successfully
• 29:53
  Speaker 1: than many other groups remains an active area of research.
• 29:57
  Speaker 1: Their upright posture and efficient locomotion may have helped in
• 30:01
  Speaker 1: some environments. Their respiratory biology, growth patterns and ability to
• 30:06
  Speaker 1: cope with climatic extremes have also been discussed. Some studies
• 30:12
  Speaker 1: have suggested that feathers or feather-like coverings in certain dinosaur
• 30:16
  Speaker 1: lineages may have helped them tolerate cooler conditions, but there
• 30:20
  Speaker 1: is unlikely to have been one magical dinosaur advantage. Survival
• 30:25
  Speaker 1: during a mass extinction suggests depends on a complicated mixture
• 30:29
  Speaker 1: of biology, geography, ecology and chance. What happened after the
• 30:35
  Speaker 1: extinction is easier to see. Ecologists use the term ecological
• 30:40
  Speaker 1: niche to describe the role an organism occupies within an ecosystem.
• 30:45
  Speaker 1: A niche includes what an animal eats, where it lives,
• 30:49
  Speaker 1: how it obtains resources and how it interacts with other
• 30:52
  Speaker 1: organisms around it. When a species disappears, the resources it
• 30:57
  Speaker 1: once used do not necessarily disappear with it. If a
• 31:00
  Speaker 1: large herbivore becomes extinct, plants remain available. If a predator disappears,
• 31:07
  Speaker 1: prey animals may temporarily face less pressure. Entire ways of
• 31:12
  Speaker 1: making a living can become vacant. These are often called
• 31:15
  Speaker 1: vacant niches. Mass extinctions create them on an enormous scale.
• 31:21
  Speaker 1: For the survivors, This can produce extraordinary evolutionary opportunities. After
• 31:27
  Speaker 1: the Entriassic extinction, dinosaur populations expanded into many of the
• 31:32
  Speaker 1: ecological roles left behind by vanished competitors. Their diversity increased,
• 31:37
  Speaker 1: their geographic range widened, and their importance within terrestrial ecosystems
• 31:43
  Speaker 1: grew substantially. What had once been one relatively modest group
• 31:48
  Speaker 1: among many was becoming something very different. As the Jurassic
• 31:52
  Speaker 1: period began, dinosaurs increasingly became the dominant large vertebrates on land.
• 31:58
  Speaker 1: Their descendants would soon include enormous long-necked herbivores, heavily armed
• 32:04
  Speaker 1: plant-eaters and powerful predators, living across landscapes from what are
• 32:09
  Speaker 1: now North America and Europe to Africa, Asia and Antarctica.
• 32:15
  Speaker 1: Yet their rise had depended partly on catastrophe. The history
• 32:19
  Speaker 1: of life is filled with these strange reversals. An event
• 32:23
  Speaker 1: that is devastating for one collection of organisms can create
• 32:27
  Speaker 1: opportunities for another. The Entriassic extinction was therefore one of
• 32:32
  Speaker 1: the great turning points in dinosaur history. For countless species,
• 32:36
  Speaker 1: it was simply the end. For the dinosaurs that survived,
• 32:40
  Speaker 1: it opened a world of possibilities. The Jurassic period began
• 32:44
  Speaker 1: around 201 million years ago. and by then the dinosaurs
• 32:49
  Speaker 1: had survived a crisis that had removed many of the
• 32:51
  Speaker 1: groups that once shared the Triassic world with them. What
• 32:55
  Speaker 1: followed was not a sudden takeover in a single place,
• 32:59
  Speaker 1: but a gradual expansion across a planet that was itself
• 33:03
  Speaker 1: changing shape. The Jurassic lasted until roughly 145 million years ago.
• 33:09
  Speaker 1: Across those tens of millions of years, dinosaurs became increasingly abundant, diverse,
• 33:18
  Speaker 1: and geographically widespread. They occupied forests, floodplains, river valleys, and
• 33:24
  Speaker 1: coastal environments across much of the world, while the continents
• 33:29
  Speaker 1: beneath them slowly began to pull apart. The supercontinent Pangea
• 33:34
  Speaker 1: was no longer stable. Tectonic forces were stretching the crust,
• 33:39
  Speaker 1: opening rifts that would eventually separate the enormous landmass into
• 33:42
  Speaker 1: smaller continents. In broad terms, the northern portion became Laurasia,
• 33:48
  Speaker 1: containing regions that would later form North America, Europe and
• 33:52
  Speaker 1: much of Asia. To the south lay Gondwana, including what
• 33:57
  Speaker 1: would eventually become South America, Africa, Antarctica, Australia and India.
• 34:04
  Speaker 1: These names describe vast regions, but the important point is
• 34:08
  Speaker 1: that geography was changing. As rifts widened, new coastlines formed.
• 34:14
  Speaker 1: Shallow seas spread into some areas. Mountain systems shifted, drainage
• 34:19
  Speaker 1: patterns changed, and populations of animals became increasingly separated from
• 34:24
  Speaker 1: one another. Those geographic barriers mattered enormously for evolution. When
• 34:30
  Speaker 1: populations are divided, they stop mixing as freely. Over long periods,
• 34:35
  Speaker 1: different environments and different evolutionary pressures can push them in
• 34:39
  Speaker 1: separate directions. A dinosaur... Population on one side of a
• 34:45
  Speaker 1: widening sea might therefore begin following a different evolutionary path
• 34:48
  Speaker 1: from its relatives elsewhere. The Jurassic world was generally warm.
• 34:53
  Speaker 1: There were no permanent polar ice caps comparable to those
• 34:56
  Speaker 1: of the modern world, and forests extended across enormous areas.
• 35:01
  Speaker 1: But those forests would not have looked quite like the
• 35:04
  Speaker 1: ones surrounding us today. Flowering plants had not yet become dominant. Instead,
• 35:11
  Speaker 1: Much of the vegetation consisted of conifers, cycads, ginkgo relatives, ferns,
• 35:18
  Speaker 1: horsetails and other ancient plant groups. In wetter areas, greenery
• 35:23
  Speaker 1: could be dense and extensive. In drier regions, vegetation was
• 35:27
  Speaker 1: more open and seasonal. Grasslands as we know them did
• 35:30
  Speaker 1: not yet stretch across the continents. The ground beneath the
• 35:34
  Speaker 1: Jurassic dinosaurs' feet was therefore often covered by very different
• 35:37
  Speaker 1: communities of plants. and among those plants walked some of
• 35:41
  Speaker 1: the largest animals ever to live on land. Sauropods became
• 35:45
  Speaker 1: extraordinarily successful during the Jurassic. These long-necked herbivores included animals
• 35:51
  Speaker 1: such as Diplodocus, Apatosaurus and Brachiosaurus. Their bodies were supported
• 35:57
  Speaker 1: by four enormous limbs, their necks extended their feeding reach
• 36:02
  Speaker 1: and their comparatively small heads allowed them to gather vegetation
• 36:07
  Speaker 1: without carrying a massive skull at the end of that neck.
• 36:10
  Speaker 1: Some sauropods reached lengths of many tens of metres. Their
• 36:14
  Speaker 1: size changed the structure of the ecosystem around them. A
• 36:18
  Speaker 1: fully grown sauropod could reach vegetation inaccessible to smaller herbivores.
• 36:23
  Speaker 1: Different species had different neck proportions, skull shapes and feeding heights,
• 36:29
  Speaker 1: allowing several enormous animals to live in the same region
• 36:32
  Speaker 1: without necessarily competing for exactly the same food. This is
• 36:38
  Speaker 1: an example of ecological partitioning. When species share an environment,
• 36:43
  Speaker 1: they can reduce direct competition by using resources differently. One
• 36:47
  Speaker 1: herbivore might feed low to the ground. Another might browse shrubs.
• 36:52
  Speaker 1: A tall sauropod could reach much higher vegetation. Even animals
• 36:57
  Speaker 1: that all appear to be doing roughly the same thing
• 36:59
  Speaker 1: from a distance may occupy subtly different ecological niches. Stegosaurs
• 37:04
  Speaker 1: were another distinctive part of Jurassic ecosystems. Their bodies were
• 37:08
  Speaker 1: much lower than those of the towering sauropods and their
• 37:11
  Speaker 1: anatomy followed a very different path. The most famous members
• 37:15
  Speaker 1: of the group carried large plates along the back and
• 37:18
  Speaker 1: powerful spikes at the end of the tail. Those tail
• 37:21
  Speaker 1: spikes were formidable defensive structures. The exact functions of the
• 37:26
  Speaker 1: back plates are more complicated and may have included visual display,
• 37:30
  Speaker 1: species recognition or other roles. But whatever their full purpose,
• 37:35
  Speaker 1: Stegosaurs were unmistakably specialised herbivores. Predators were diversifying as well.
• 37:42
  Speaker 1: Large theropods such as Allosaurus occupied important predatory roles in
• 37:46
  Speaker 1: late Jurassic North America, alongside other carnivorous dinosaurs of different sizes.
• 37:53
  Speaker 1: These predators were not interchangeable. They differed in body size,
• 37:57
  Speaker 1: skull shape, teeth, limb proportions and likely hunting behaviour. Some
• 38:04
  Speaker 1: may have targeted relatively small prey, while others were capable
• 38:08
  Speaker 1: of attacking much larger animals or feeding from carcasses when
• 38:12
  Speaker 1: opportunities arose. Again, ecological partitioning allowed several predators to inhabit
• 38:18
  Speaker 1: the same broad environment. One of our clearest windows into
• 38:23
  Speaker 1: this world comes from the Morrison Formation of Western North America.
• 38:27
  Speaker 1: Its rocks preserve an extraordinary late Jurassic ecosystem containing dinosaurs
• 38:33
  Speaker 1: including Allosaurus, Stegosaurus, Diplodocus, Apatosaurus and several other sauropods and
• 38:40
  Speaker 1: smaller species. But the Morrison Formation represents one region of
• 38:45
  Speaker 1: the Jurassic world. Thousands of kilometres away, another remarkable fossil
• 38:51
  Speaker 1: record was being formed in what is now Tanzania. The
• 38:55
  Speaker 1: Tendaguru beds preserve their own late Jurassic dinosaur community. Sauropods,
• 39:01
  Speaker 1: theropods and other dinosaurs lived there too, but the species
• 39:04
  Speaker 1: were not simply identical copies of those found in North America.
• 39:09
  Speaker 1: That distinction is important. Popular images of the Jurassic sometimes
• 39:14
  Speaker 1: gather every famous dinosaur into one convenient landscape, as if
• 39:19
  Speaker 1: the entire planet were one enormous wildlife park. Real ecosystems
• 39:24
  Speaker 1: were much more complicated. Dinosaurs were separated by geography, and
• 39:30
  Speaker 1: sometimes by millions of years. Even animals living during broadly
• 39:35
  Speaker 1: similar periods could occupy continents far apart from one another.
• 39:39
  Speaker 1: And not everything in these ecosystems was enormous. Small dinosaurs
• 39:43
  Speaker 1: moved beneath the feet of the giants. There were small, Ornithischians,
• 39:49
  Speaker 1: lightly built herbivores and omnivores that rarely received the same
• 39:52
  Speaker 1: attention as sauropods or stegosaurs. Small theropods occupied predatory and
• 39:57
  Speaker 1: probably opportunistic feeding roles. Some were scarcely larger than modern birds.
• 40:03
  Speaker 1: Mammals also lived in the Jurassic, although most were small.
• 40:06
  Speaker 1: Pterosaurs flew overhead. Crocodilian relatives inhabited waterways and surrounding landscapes.
• 40:14
  Speaker 1: Insects filled the vegetation. while fish and other aquatic animals
• 40:18
  Speaker 1: occupied rivers and lakes. The Jurassic was therefore not simply
• 40:22
  Speaker 1: an age of giants. It was a complete living world.
• 40:26
  Speaker 1: The giants merely happened to be rather difficult to overlook.
• 40:30
  Speaker 1: By this point, dinosaur dominance had become a global phenomenon.
• 40:34
  Speaker 1: Different dinosaur lineages occupied major terrestrial roles across an extraordinary
• 40:38
  Speaker 1: geographic range, yet even at the height of their success,
• 40:42
  Speaker 1: nothing about them was fixed. The continents continued moving. Climate
• 40:47
  Speaker 1: continued changing. Plant communities shifted. Populations became isolated and reunited.
• 40:56
  Speaker 1: New species appeared while others disappeared. The Jurassic dinosaurs were
• 41:00
  Speaker 1: not standing still in some perfect prehistoric world. They were
• 41:04
  Speaker 1: continuously responding to a planet in motion. And as that
• 41:08
  Speaker 1: world changed around them, evolution kept producing new forms, new
• 41:12
  Speaker 1: sizes and new ways of surviving. By the Jurassic period,
• 41:17
  Speaker 1: dinosaur evolution had produced one of the most extraordinary body
• 41:21
  Speaker 1: plans ever seen on land. These were the sauropods. Sauropods
• 41:25
  Speaker 1: included some of the largest animals ever to walk on
• 41:28
  Speaker 1: the Earth. Depending on the species, some reached lengths of
• 41:32
  Speaker 1: several tens of metres and masses measured in many tens
• 41:36
  Speaker 1: of tonnes. A few of the most enormous forms may
• 41:40
  Speaker 1: have rivaled or exceeded the mass of several large elephants
• 41:44
  Speaker 1: combined many times over. Their sheer size can make them
• 41:48
  Speaker 1: seem almost impossible. But sauropod gigantism was not the result
• 41:53
  Speaker 1: of one single adaptation. It emerged from a combination of
• 41:57
  Speaker 1: anatomical and physiological features that worked together. One of the
• 42:01
  Speaker 1: most obvious was the neck. A sauropod could reach a
• 42:05
  Speaker 1: huge feeding area without moving its entire body each time
• 42:08
  Speaker 1: it wanted another mouthful. Instead of walking several steps to
• 42:12
  Speaker 1: every new patch of vegetation, It could sweep its head
• 42:15
  Speaker 1: and neck through a broad volume of space. That created
• 42:18
  Speaker 1: what might be called an enormous feeding envelope. The exact
• 42:22
  Speaker 1: posture of sauropod necks is still studied, and different species
• 42:26
  Speaker 1: probably held and moved them in different ways. Some may
• 42:30
  Speaker 1: have browsed higher into trees. Others may have fed more
• 42:33
  Speaker 1: horizontally or lower to the ground. The important point is
• 42:37
  Speaker 1: that a long neck allowed access to food while keeping
• 42:39
  Speaker 1: the body relatively stationary. That matters when the body weighs
• 42:43
  Speaker 1: dozens of tonnes. Moving such an animal required energy. Reaching
• 42:48
  Speaker 1: with the neck was cheaper than constantly shifting the entire body.
• 42:52
  Speaker 1: Sauropods also had relatively small heads. That may seem odd
• 42:56
  Speaker 1: at first, because large mammals often have large skulls and
• 42:59
  Speaker 1: powerful chewing muscles. But a lighter head is much easier
• 43:02
  Speaker 1: to support at the end of a long neck. Sauropods
• 43:06
  Speaker 1: did not need enormous jaws filled with grinding teeth. because
• 43:09
  Speaker 1: many species did not process food extensively in the mouth.
• 43:13
  Speaker 1: Instead they often cropped vegetation and swallowed it after relatively
• 43:17
  Speaker 1: limited chewing. The digestive system then did much of the work.
• 43:22
  Speaker 1: This is very different from the feeding strategy of many
• 43:24
  Speaker 1: large mammalian herbivores. A horse, for example, spends a great
• 43:29
  Speaker 1: deal of time grinding plant material with complex teeth. Many
• 43:34
  Speaker 1: sauropods relied more heavily on taking in large quantities of
• 43:37
  Speaker 1: vegetation and allowing digestion to continue internally over time. That
• 43:42
  Speaker 1: strategy supported a relatively small skull, which in turn helped
• 43:46
  Speaker 1: make the long neck more practical. Their limbs were equally important.
• 43:51
  Speaker 1: Sauropod legs became thick, strong and column-like. Rather than being
• 43:56
  Speaker 1: built primarily for speed, they were arranged to support enormous
• 43:59
  Speaker 1: weight efficiently. The limbs sat beneath the body, carrying mass
• 44:04
  Speaker 1: vertically through the skeleton. This is a very different engineering
• 44:08
  Speaker 1: problem from the one faced by a small, agile theropod.
• 44:12
  Speaker 1: A giant animal does not need to turn sharply or
• 44:15
  Speaker 1: sprint constantly. It needs to stand, walk and support itself
• 44:20
  Speaker 1: without placing impossible stress on its bones and joints. Sauropod
• 44:24
  Speaker 1: bodies were therefore built around stability. But there was another
• 44:28
  Speaker 1: remarkable feature hidden inside their skeletons. Sauropods possessed an air
• 44:33
  Speaker 1: sac system linked to respiration. broadly comparable in as principal
• 44:38
  Speaker 1: to the air sacs found in living birds. These air
• 44:41
  Speaker 1: sacs extended through the body and in many sauropods invaded
• 44:45
  Speaker 1: parts of the vertebral column. This produced spaces within the bones.
• 44:50
  Speaker 1: The result was a skeleton that could remain large and
• 44:52
  Speaker 1: strong without being completely solid. In simple terms, some vertebrae
• 44:57
  Speaker 1: were more like carefully reinforced structures than dense blocks of bone.
• 45:01
  Speaker 1: That reduced weight. For an animal supporting an extremely long neck,
• 45:06
  Speaker 1: this was especially useful. A neck made entirely from solid,
• 45:11
  Speaker 1: heavy vertebrae would have placed far greater demands on muscles,
• 45:14
  Speaker 1: joints and the rest of the skeleton. The air sac
• 45:18
  Speaker 1: system also suggests that sauropods had a sophisticated respiratory system.
• 45:23
  Speaker 1: Living birds move air through their lungs in a highly
• 45:26
  Speaker 1: efficient way, and sauropods likely shared at least some aspects
• 45:31
  Speaker 1: of this broader anatomical arrangement. respiration, skeletal lightening, feeding strategy
• 45:38
  Speaker 1: and limb structure all contributed to making enormous size possible.
• 45:43
  Speaker 1: Then there was growth. Every giant sauropod began life inside
• 45:48
  Speaker 1: an egg. This fact alone makes their adult size even
• 45:51
  Speaker 1: more remarkable. Sauropod eggs were not proportionally enormous. Hatchlings began
• 45:56
  Speaker 1: life at a tiny fraction of adult mass. To become
• 46:00
  Speaker 1: one of the largest animals ever to live on land,
• 46:03
  Speaker 1: A young sauropod therefore had to increase its body mass
• 46:06
  Speaker 1: at an astonishing rate. Scientists can investigate this through bone histology.
• 46:12
  Speaker 1: Bone histology involves examining very thin sections of fossil bone
• 46:16
  Speaker 1: under a microscope. The internal structure can reveal how quickly
• 46:20
  Speaker 1: bone tissue was deposited, whether growth slowed seasonally, and how
• 46:25
  Speaker 1: growth changed as an animal aged. Sauropod bones show evidence
• 46:30
  Speaker 1: of rapid growth. especially during earlier stages of life. They
• 46:34
  Speaker 1: were not simply reptiles growing slowly for centuries. Many appear
• 46:39
  Speaker 1: to have grown much faster than that traditional picture would suggest.
• 46:43
  Speaker 1: Rapid growth allowed them to pass through vulnerable juvenile stages
• 46:47
  Speaker 1: and move toward the enormous body sizes of adulthood. Once
• 46:52
  Speaker 1: fully grown, sheer size itself could become a defence. A
• 46:56
  Speaker 1: small sauropod could be attacked by a wide range of predators.
• 47:00
  Speaker 1: A healthy adult weighing many tens of tons was a
• 47:03
  Speaker 1: very different prospect. Predators may still have targeted injured, young
• 47:08
  Speaker 1: or isolated individuals, but attacking a full-sized giant would have
• 47:13
  Speaker 1: carried obvious risks. The Jurassic produced several famous sauropods, but
• 47:18
  Speaker 1: they should not all be imagined living side by side
• 47:21
  Speaker 1: in one enormous herd. Diplodocus lived in what is now
• 47:25
  Speaker 1: western North America during the late Jurassic. It had an
• 47:28
  Speaker 1: extremely long tail, a relatively slender build for a sauropod,
• 47:33
  Speaker 1: and a very long neck. Brachiosaurus also lived in late
• 47:37
  Speaker 1: Jurassic North America, but its proportions were different. Its forelimbs
• 47:42
  Speaker 1: were longer than its hindlimbs, giving the body a distinctive
• 47:46
  Speaker 1: upward slope toward the shoulders. Other related forms lived elsewhere.
• 47:52
  Speaker 1: Different sauropod lineages evolved across different continents and at different times. Later,
• 47:58
  Speaker 1: during the Cretaceous, titanosaurs would become especially important and would
• 48:02
  Speaker 1: include some of the largest terrestrial animals known. Sauropods were
• 48:06
  Speaker 1: therefore not one single type of giant. They were a
• 48:09
  Speaker 1: diverse evolutionary radiation built around variations of the long-necked, large-bodied
• 48:15
  Speaker 1: herbivore form, and their success shows something important about dinosaur
• 48:20
  Speaker 1: evolution as a whole. There was no perfect dinosaur size.
• 48:24
  Speaker 1: Gigantism was extraordinarily successful in some ecological roles. Tiny body
• 48:30
  Speaker 1: size was equally successful in others. While sauropods were evolving
• 48:35
  Speaker 1: into animals weighing many tens of tons, other dinosaur lineages
• 48:39
  Speaker 1: contained species smaller than a modern chicken. Those animals were
• 48:44
  Speaker 1: not failures because they were small. They simply occupied different niches.
• 48:49
  Speaker 1: Evolution rewards survival and reproduction, not impressive measurements. The larger
• 48:55
  Speaker 1: sauropods represented one extreme of what the dinosaur body plan
• 48:59
  Speaker 1: could achieve. Their long necks expanded their feeding range. Their
• 49:03
  Speaker 1: small heads reduced the burden at the end of those necks.
• 49:07
  Speaker 1: Their column-like limbs supported immense mass. Their air-filled vertebrae helped
• 49:12
  Speaker 1: reduce skeletal weight. Their feeding strategy allowed them to gather
• 49:16
  Speaker 1: huge quantities of plant material without spending all day chewing
• 49:20
  Speaker 1: it into paste. And rapid growth carried them from relatively
• 49:25
  Speaker 1: small hatchlings to enormous adults. No single feature explains their size.
• 49:31
  Speaker 1: It was the combination that mattered. Over millions of years,
• 49:35
  Speaker 1: each part of the system reinforced the others. The result
• 49:40
  Speaker 1: was something no land animal before or since has quite matched.
• 49:44
  Speaker 1: A living creature several tens of metres long, supported entirely
• 49:48
  Speaker 1: by its own skeleton and muscles, moving through forests and
• 49:51
  Speaker 1: floodplains on four enormous legs. Sauropods were not simply large dinosaurs.
• 49:59
  Speaker 1: They were one of evolution's most extreme solutions to the
• 50:02
  Speaker 1: problem of living on land. By the Jurassic period, Dinosaurs
• 50:07
  Speaker 1: were not simply becoming larger and more diverse. They were
• 50:10
  Speaker 1: also becoming more deeply shaped by one another. Every predator
• 50:14
  Speaker 1: exerted pressure on the animals it hunted. Every herbivore that
• 50:18
  Speaker 1: survived an attack passed on whatever advantages had helped it escape.
• 50:23
  Speaker 1: Across millions of years, this constant interaction between attack and
• 50:27
  Speaker 1: defence influenced teeth, claws, armour, tails, speed, body size and behaviour.
• 50:35
  Speaker 1: Predation was not an occasional interruption to dinosaur life. It
• 50:39
  Speaker 1: was one of the forces helping to shape it. Among
• 50:42
  Speaker 1: the best-known large Jurassic predators was Allosaurus. Allosaurus lived in
• 50:47
  Speaker 1: western North America during the late Jurassic and is especially
• 50:51
  Speaker 1: well represented in the fossil record. Its skeleton reveals a
• 50:55
  Speaker 1: large theropod built for active predation, with powerful hind limbs,
• 51:00
  Speaker 1: grasping forelimbs, a long balancing tail and a skull filled
• 51:05
  Speaker 1: with sharp teeth. Those teeth were not shaped for grinding
• 51:08
  Speaker 1: or crushing vegetation. They were recurved and serrated. In other words,
• 51:14
  Speaker 1: they were biological cutting tools. The edges carried tiny serrations
• 51:18
  Speaker 1: that could help slice through flesh, allowing the animal to
• 51:22
  Speaker 1: remove pieces of tissue during feeding. The skull itself was
• 51:26
  Speaker 1: relatively lightly built compared with the much deeper and more
• 51:29
  Speaker 1: heavily reinforced skull of a later predator such as Tyrannosaurus.
• 51:34
  Speaker 1: That difference matters. It suggests that large theropods did not
• 51:38
  Speaker 1: all feed in exactly the same way. Allosaurus had its
• 51:42
  Speaker 1: own combination of skull strength, jaw mechanics, neck musculature and
• 51:48
  Speaker 1: tooth shape. Paleontologists have proposed different feeding strategies for it,
• 51:53
  Speaker 1: including repeated slashing bites and powerful movements of the head
• 51:57
  Speaker 1: and neck. But fossils cannot replay a hunt for us.
• 52:02
  Speaker 1: They can reveal what the animal was physically capable of doing.
• 52:05
  Speaker 1: They cannot tell us exactly how every individual behaved in
• 52:09
  Speaker 1: every encounter. The same caution applies when we find evidence
• 52:14
  Speaker 1: of injury. Some Allosaurus fossils preserve healed fractures, damaged ribs
• 52:20
  Speaker 1: and other signs of trauma. Those injuries can tell us
• 52:23
  Speaker 1: that the animal survived serious physical stress. They may have
• 52:28
  Speaker 1: resulted from struggles with prey, conflicts with other predators, accidents
• 52:33
  Speaker 1: or some combination of these. A healed injury is a
• 52:36
  Speaker 1: record of survival. It is not a complete eyewitness account.
• 52:41
  Speaker 1: Across the same late Jurassic landscapes lived Stegosaurus. Stegosaurus was
• 52:47
  Speaker 1: built around an almost entirely different evolutionary problem. It was
• 52:51
  Speaker 1: a herbivore. Instead of pursuing other animals, it needed to
• 52:55
  Speaker 1: avoid becoming somebody else's meal. Its back carried two rows
• 52:59
  Speaker 1: of large plates, while the end of the tail was
• 53:03
  Speaker 1: equipped with long spikes. The defensive potential of those tail
• 53:07
  Speaker 1: spikes is supported by both anatomy and fossil evidence. A
• 53:11
  Speaker 1: powerful sideways swing could have turned the tail into a
• 53:15
  Speaker 1: dangerous weapon. There is even fossil evidence of injuries in
• 53:19
  Speaker 1: large theropods that may be consistent with encounters involving stegosaur
• 53:23
  Speaker 1: tail spikes. The plates along the back are more mysterious.
• 53:28
  Speaker 1: Scientists have proposed several possible functions over the years. One
• 53:32
  Speaker 1: idea was thermoregulation, in which the plates may have helped
• 53:35
  Speaker 1: exchange heat with the environment. Another possibility is display. The
• 53:40
  Speaker 1: plates may have helped animals recognise one another. signal maturity
• 53:45
  Speaker 1: or advertise to potential mates and rivals. Their precise function
• 53:49
  Speaker 1: remains debated, and it is possible they served more than
• 53:52
  Speaker 1: one purpose. That uncertainty is worth keeping. It is tempting
• 53:57
  Speaker 1: to assign a tidy job to every strange structure on
• 54:00
  Speaker 1: an extinct animal. Real evolution is often less tidy. A
• 54:05
  Speaker 1: feature can begin serving one function and later acquire another.
• 54:10
  Speaker 1: Some structures may also carry several advantages at once. Sauropods
• 54:15
  Speaker 1: followed a different defensive strategy again. For the largest adult,
• 54:19
  Speaker 1: size itself was protection. A fully grown sauropod weighing many
• 54:23
  Speaker 1: tens of tonnes would have been an extremely dangerous target.
• 54:28
  Speaker 1: Even a large predator faced the risk of being kicked, struck,
• 54:32
  Speaker 1: crushed or injured during an attack. That does not mean
• 54:36
  Speaker 1: adult sauropods were invulnerable. Old, injured or isolated animals may
• 54:41
  Speaker 1: have been more vulnerable. and groups of predators may sometimes
• 54:45
  Speaker 1: have tackled larger prey. But sheer body mass changed the calculation.
• 54:51
  Speaker 1: A young sauropod faced a very different world. Sauropods hatched
• 54:56
  Speaker 1: from eggs, so juveniles began life tiny compared with their
• 55:00
  Speaker 1: eventual adult size. For years they would have occupied a
• 55:04
  Speaker 1: much more vulnerable position in the food web. This difference
• 55:07
  Speaker 1: between juveniles and adults is important because one species could
• 55:11
  Speaker 1: move through several ecological roles during its lifetime. A hatchling
• 55:15
  Speaker 1: could be prey for many animals. A fully grown adult
• 55:18
  Speaker 1: might have very few predators capable of attacking it successfully.
• 55:22
  Speaker 1: Teeth provide some of the clearest evidence of these different roles.
• 55:26
  Speaker 1: Carnivorous theropods often carried sharp, serrated teeth suited to gripping
• 55:30
  Speaker 1: and cutting flesh. Herbivorous dinosaurs evolved very different feeding structures.
• 55:36
  Speaker 1: Stegosaurs had relatively small teeth suited to cropping and processing
• 55:40
  Speaker 1: plant material. Other herbivorous lineages developed broader teeth, beaks or
• 55:46
  Speaker 1: complex arrangements capable of handling increasingly tough vegetation. The teeth
• 55:51
  Speaker 1: were not simply passive parts of the skull. They were
• 55:54
  Speaker 1: specialised tools shaped by diet, and sometimes those tools leave
• 55:58
  Speaker 1: direct evidence behind. Toothmarks preserved on fossil bones can reveal
• 56:03
  Speaker 1: that a carcass was fed upon, Occasionally the spacing and
• 56:07
  Speaker 1: shape of the marks can help identify the kind of
• 56:10
  Speaker 1: animal responsible. A healed bite mark is even more informative.
• 56:15
  Speaker 1: If bone grew back around an injury, then the animal
• 56:18
  Speaker 1: survived the attack. That means predator and prey were alive
• 56:22
  Speaker 1: at the same time, in the same environment, and physically interacted.
• 56:28
  Speaker 1: Trackways offer another kind of evidence. Fossilised footprints can preserve
• 56:32
  Speaker 1: movement across a surface that existed more than 100 million
• 56:36
  Speaker 1: years ago, they can reveal direction, stride length, approximate speed,
• 56:42
  Speaker 1: and whether several individuals travelled through the same area. In
• 56:46
  Speaker 1: rare cases, trackways appear to record interactions between different kinds
• 56:51
  Speaker 1: of animals. But interpretation requires care. Two tracks crossing the
• 56:56
  Speaker 1: same patch of ground do not automatically mean one animal
• 56:59
  Speaker 1: was chasing another. The tracks may have been made hours
• 57:03
  Speaker 1: days or even longer apart, paleontology is often a matter
• 57:08
  Speaker 1: of knowing exactly how far the evidence allows us to go.
• 57:12
  Speaker 1: Other clues are more direct. Preserved stomach contents can occasionally
• 57:16
  Speaker 1: reveal what an animal had eaten shortly before death. Coprolites,
• 57:21
  Speaker 1: or fossilised droppings, can contain fragments of bone or plant material.
• 57:26
  Speaker 1: These may not be the most glamorous fossils in a
• 57:28
  Speaker 1: museum collection, but they can be remarkably informative. An animal's
• 57:33
  Speaker 1: waist can sometimes tell us more about its diet than
• 57:36
  Speaker 1: its skeleton does. Predators, however, should not be imagined as
• 57:40
  Speaker 1: permanently charging at the largest available prey. A real carnivore
• 57:45
  Speaker 1: must manage risk. An injury can mean starvation. A broken
• 57:49
  Speaker 1: limb or damaged jaw could be fatal. Large predators, probably
• 57:54
  Speaker 1: hunted animals they could realistically overpower, took advantage of vulnerable
• 57:58
  Speaker 1: individuals and scavenged carcasses when the opportunity arose. Scavenging is
• 58:04
  Speaker 1: not somehow inferior to hunting. It is free food. Most
• 58:08
  Speaker 1: modern predators will take advantage of it when they can,
• 58:11
  Speaker 1: and there is little reason to imagine dinosaurs behaving differently.
• 58:16
  Speaker 1: The Jurassic landscape was therefore not an endless sequence of
• 58:19
  Speaker 1: dramatic battles. Most animals spent far more time feeding, walking, resting,
• 58:24
  Speaker 1: avoiding danger and simply staying alive. And the food web
• 58:28
  Speaker 1: extended far beyond dinosaurs. Plants formed the foundation of terrestrial ecosystems.
• 58:34
  Speaker 1: Insects fed on vegetation and on one another. Small mammals
• 58:38
  Speaker 1: moved through undergrowth and burrows. Pterosaurs occupied the skies. Crocodilian
• 58:44
  Speaker 1: relatives lived in rivers and along shorelines. Fish, amphibians and
• 58:49
  Speaker 1: countless smaller organisms filled aquatic environments. Dinosaurs were woven into
• 58:54
  Speaker 1: all of this. They were not isolated giants standing against
• 58:58
  Speaker 1: empty backgrounds. Every Allosaurus depended ultimately on the productivity of plants,
• 59:04
  Speaker 1: because the herbivores it ate depended on them first. Every
• 59:08
  Speaker 1: sauropod was part of a network involving vegetation, microbes, parasites,
• 59:14
  Speaker 1: scavengers and predators. Every Stegosaurus lived within an ecosystem containing
• 59:19
  Speaker 1: threats it could defend against and resources it needed to find.
• 59:24
  Speaker 1: Seen this way, dinosaur anatomy becomes a record of relationships.
• 59:29
  Speaker 1: A serrated tooth tells us something about flesh. A tail
• 59:32
  Speaker 1: spike tells us something about danger. Armour tells us that
• 59:35
  Speaker 1: being difficult to bite could be valuable. Gigantic body size
• 59:41
  Speaker 1: tells us that growing beyond the comfortable reach of predators
• 59:44
  Speaker 1: could be useful too. Across millions of years, predators and
• 59:48
  Speaker 1: prey continually altered the challenges faced by one another. Neither
• 59:53
  Speaker 1: side was trying to produce some perfect weapon or perfect defence.
• 59:57
  Speaker 1: Evolution has no plan But generation after generation, the individuals
• 1:00:01
  Speaker 1: that survived left descendants. And in their bones, teeth, armour
• 1:00:07
  Speaker 1: and scars, some of those ancient struggles can still be
• 1:00:11
  Speaker 1: read today. Every dinosaur, no matter how enormous it eventually became,
• 1:00:17
  Speaker 1: began life in an egg. That simple fact is easy
• 1:00:21
  Speaker 1: to overlook when we think of animals weighing many tonnes.
• 1:00:25
  Speaker 1: but it means every giant passed through a series of
• 1:00:28
  Speaker 1: dramatic changes before reaching adulthood. A sauropod that eventually towered
• 1:00:34
  Speaker 1: over the landscape began as a small hatchling. A large
• 1:00:37
  Speaker 1: predator once had to survive as a vulnerable juvenile. Even
• 1:00:41
  Speaker 1: the most imposing dinosaur spent part of its life at
• 1:00:44
  Speaker 1: a size where danger came from many more directions. Fossilised
• 1:00:48
  Speaker 1: eggs are among the most intimate pieces of evidence we
• 1:00:52
  Speaker 1: have for dinosaur life. Some of the oldest known dinosaur
• 1:00:55
  Speaker 1: eggs date back roughly 230 million years. Over time, paleontologists
• 1:01:01
  Speaker 1: have found not only individual eggs, but entire nests, nesting grounds, and,
• 1:01:07
  Speaker 1: in rare cases, embryos preserved inside them. These discoveries transform
• 1:01:13
  Speaker 1: the way scientists think about dinosaur reproduction. Eggs reveal that
• 1:01:18
  Speaker 1: different dinosaur groups used different nesting strategies. Some buried their eggs.
• 1:01:23
  Speaker 1: Others arranged them in carefully organised clutches. In some places,
• 1:01:28
  Speaker 1: repeated nesting in the same area suggests that groups returned
• 1:01:31
  Speaker 1: to particular sites over generations. One of the best-known examples
• 1:01:36
  Speaker 1: is Mayasaura. Mayasaura was a hadrosaur that lived during the
• 1:01:40
  Speaker 1: late Cretaceous in what is now Montana. Fossil sites associated
• 1:01:44
  Speaker 1: with the animal preserved nests, eggs and juveniles in large concentrations.
• 1:01:49
  Speaker 1: These finds strongly support the idea that Mayasaura nested in colonies.
• 1:01:54
  Speaker 1: They have also played an important role in discussions about
• 1:01:56
  Speaker 1: parental care. Some juvenile fossils were discovered within nests and
• 1:02:01
  Speaker 1: appear to have remained there for at least part of
• 1:02:03
  Speaker 1: their early development. This led to the suggestion that adults
• 1:02:07
  Speaker 1: may have protected or fed their young. That possibility is plausible,
• 1:02:11
  Speaker 1: but the details are still debated. The fossils support nesting
• 1:02:15
  Speaker 1: behaviour and some degree of association between adults and young.
• 1:02:20
  Speaker 1: They do not allow us to reconstruct every feeding interaction
• 1:02:24
  Speaker 1: with certainty. Other dinosaurs provide more direct evidence of brooding.
• 1:02:29
  Speaker 1: Oviraptorid dinosaurs such as Sitipati have been found preserved sitting
• 1:02:34
  Speaker 1: over nests in a posture remarkably similar to that of
• 1:02:37
  Speaker 1: modern birds. The body is positioned above the eggs, with
• 1:02:41
  Speaker 1: the limbs arranged around the clutch. That is powerful evidence
• 1:02:44
  Speaker 1: that at least some non-avian dinosaurs actively brooded their eggs.
• 1:02:49
  Speaker 1: For a long time, the close relationship between birds and
• 1:02:53
  Speaker 1: dinosaurs was hidden by old assumptions about reptile behaviour. Today,
• 1:02:58
  Speaker 1: a dinosaur sitting carefully over a nest seems much less surprising.
• 1:03:03
  Speaker 1: Once the eggs hatched, growth became one of the defining
• 1:03:07
  Speaker 1: challenges of dinosaur life. Paleontologists can study this through bone histology.
• 1:03:13
  Speaker 1: A thin section of fossil bone preserves microscopic structures that
• 1:03:17
  Speaker 1: reveal how the tissue formed. growth rings, changes in bone density,
• 1:03:22
  Speaker 1: and the organisation of blood vessels can provide clues about age,
• 1:03:27
  Speaker 1: growth rate and periods when development slowed. Some dinosaurs grew rapidly.
• 1:03:33
  Speaker 1: Others followed more complex patterns, with growth slowing during difficult
• 1:03:37
  Speaker 1: seasons and accelerating when conditions improved. These patterns helped reveal
• 1:03:42
  Speaker 1: that dinosaurs were not simply oversized versions of modern reptiles.
• 1:03:46
  Speaker 1: Their physiology was more varied. For much of the 20th century,
• 1:03:51
  Speaker 1: dinosaurs were often imagined as uniformly sluggish and cold-blooded. That
• 1:03:56
  Speaker 1: picture has largely disappeared. Scientists now recognise that metabolism among
• 1:04:01
  Speaker 1: dinosaurs was probably diverse and depended on lineage, body size
• 1:04:06
  Speaker 1: and ecology. Some groups likely maintained relatively high metabolic rates.
• 1:04:11
  Speaker 1: Others may have operated differently. Large body size itself can
• 1:04:15
  Speaker 1: help stabilise temperature. while feathers could provide insulation in smaller species.
• 1:04:21
  Speaker 1: There is unlikely to have been one universal dinosaur metabolism.
• 1:04:25
  Speaker 1: The shift away from the old image of slow, lumbering
• 1:04:29
  Speaker 1: dinosaurs became especially important during what is often called the
• 1:04:33
  Speaker 1: Dinosaur Renaissance. Paleontologists John Ostrom and Robert Bakker were central
• 1:04:40
  Speaker 1: to this change in the 20th century. Their work helped
• 1:04:43
  Speaker 1: popularise a more active view of dinosaurs as dynamic animals,
• 1:04:47
  Speaker 1: capable of complex movement, rapid growth and sophisticated behaviour. Evidence
• 1:04:53
  Speaker 1: for social behaviour has also accumulated, but it must be
• 1:04:56
  Speaker 1: interpreted carefully. Bone beds containing many individuals of the same
• 1:05:01
  Speaker 1: species can suggest group living. Trackways showing multiple dinosaurs moving
• 1:05:06
  Speaker 1: in the same direction can do the same, but neither
• 1:05:09
  Speaker 1: automatically proves permanent herding. Animals may gather temporarily around water,
• 1:05:14
  Speaker 1: food or breeding sites without living in stable social groups.
• 1:05:18
  Speaker 1: Even when several individuals are found together, the exact nature
• 1:05:22
  Speaker 1: of their relationship remains uncertain. Communication is harder still to reconstruct.
• 1:05:29
  Speaker 1: Some dinosaurs carried large crests, horns, frills or elaborate feathers.
• 1:05:35
  Speaker 1: These structures may have helped with display, species recognition, courtship
• 1:05:39
  Speaker 1: or competition. In living animals, visual structures often serve several
• 1:05:43
  Speaker 1: purposes at once. A crest may be useful for attracting
• 1:05:47
  Speaker 1: mates while also signalling identity to rivals. The same may
• 1:05:52
  Speaker 1: have been true for dinosaurs, but fossil evidence rarely tells
• 1:05:56
  Speaker 1: us exactly what colour a display was, what sound accompanied it,
• 1:06:00
  Speaker 1: or how individuals responded. That is where reconstruction must remain cautious.
• 1:06:08
  Speaker 1: The everyday life of a dinosaur was therefore probably rich
• 1:06:10
  Speaker 1: with behaviour, but only fragments of it survive. Nests show reproduction.
• 1:06:16
  Speaker 1: Embryos preserve development. Bone tissue records growth. Trackways capture movement.
• 1:06:24
  Speaker 1: Injuries preserve moments of stress and survival. And occasionally, a
• 1:06:28
  Speaker 1: fossilised adult sitting over eggs gives us something almost startlingly familiar.
• 1:06:34
  Speaker 1: These were not static skeletons waiting to become museum exhibits.
• 1:06:39
  Speaker 1: They were animals that hatched, grew, moved, competed, reproduced and
• 1:06:43
  Speaker 1: cared for their young in ways that were sometimes surprisingly recognisable.
• 1:06:48
  Speaker 1: The closer we look at the evidence, the more the
• 1:06:50
  Speaker 1: dinosaurs begin to feel less like distant monsters and more
• 1:06:54
  Speaker 1: like living creatures with ordinary biological problems. They simply happen
• 1:06:59
  Speaker 1: to solve those problems in a world very different from
• 1:07:01
  Speaker 1: our own. Feathers appeared in dinosaurs long before there were
• 1:07:05
  Speaker 1: modern birds. That is one of the most important changes
• 1:07:08
  Speaker 1: in how we now picture the dinosaur world. For much
• 1:07:11
  Speaker 1: of the 20th century, dinosaurs were usually reconstructed as uniformly
• 1:07:16
  Speaker 1: scaly reptiles. Some certainly did have scales, and many probably
• 1:07:21
  Speaker 1: carried combinations of scales and feathers. But discoveries over the
• 1:07:26
  Speaker 1: past few decades have shown that feather-like coverings were widespread
• 1:07:30
  Speaker 1: among many theropod dinosaurs. The earliest feathers were probably not
• 1:07:34
  Speaker 1: built for flight. Simple filament-like structures could have provided insulation,
• 1:07:40
  Speaker 1: helping smaller dinosaurs retain body heat. Feathers may also have
• 1:07:44
  Speaker 1: played roles in display, camouflage or communication. Only later did
• 1:07:49
  Speaker 1: more specialised feathers evolve into the complex structures capable of
• 1:07:53
  Speaker 1: supporting powered flight. One of the fossils that helped transform
• 1:07:57
  Speaker 1: this picture was Sinosauropteryx. Cynosauropteryx lived during the early Cretaceous
• 1:08:03
  Speaker 1: in what is now China. When it was described during
• 1:08:06
  Speaker 1: the 1990s, its fossils showed a covering of fine filamentous
• 1:08:10
  Speaker 1: structures preserved around the body. It was not a modern bird.
• 1:08:15
  Speaker 1: It was a small non-bird theropod dinosaur, and yet its
• 1:08:18
  Speaker 1: body was clearly not simply wrapped in bare reptilian skin.
• 1:08:23
  Speaker 1: This discovery became part of a much larger wave of
• 1:08:26
  Speaker 1: fossils from China. revealing feathered dinosaurs in remarkable detail. Some
• 1:08:32
  Speaker 1: showed simple filaments, others carried more elaborate feathers, and suddenly
• 1:08:37
  Speaker 1: the evolutionary distance between dinosaurs and birds began to look
• 1:08:41
  Speaker 1: much smaller. But the connection had been suspected much earlier.
• 1:08:47
  Speaker 1: Around 150 million years ago, during the late Jurassic, an
• 1:08:52
  Speaker 1: animal called Archaeopteryx lived in what is now Germany. Archaeopteryx
• 1:08:57
  Speaker 1: is one of the most famous transitional fossils in the
• 1:09:00
  Speaker 1: history of paleontology. Its body combined features that seemed strikingly
• 1:09:05
  Speaker 1: bird-like with others that were unmistakably dinosaurian. It had well-developed feathers,
• 1:09:11
  Speaker 1: it had wings, but it also had teeth. Its hands
• 1:09:15
  Speaker 1: retained clawed fingers. and behind it extended a long bony tail,
• 1:09:21
  Speaker 1: very unlike the shortened tail of modern birds. When the
• 1:09:24
  Speaker 1: first important Archaeopteryx fossils became known in the 19th century,
• 1:09:29
  Speaker 1: the timing was remarkable. Charles Darwin had published his theory
• 1:09:35
  Speaker 1: of evolution by natural selection only shortly before. The idea
• 1:09:39
  Speaker 1: that major groups of organisms could be connected through gradual
• 1:09:43
  Speaker 1: evolutionary change was still deeply controversial. Archaeopteryx seemed to offer
• 1:09:48
  Speaker 1: a vivid example of that continuity. Thomas Henry Huxley, one
• 1:09:53
  Speaker 1: of the strongest early supporters of Darwin's ideas, compared the
• 1:09:57
  Speaker 1: skeletons of birds with those of small dinosaurs and recognised
• 1:10:01
  Speaker 1: important similarities. He argued that birds and dinosaurs were closely related.
• 1:10:07
  Speaker 1: That idea did not immediately become universally accepted. For decades,
• 1:10:12
  Speaker 1: other explanations competed with it. Then, During the 1960s and 1970s,
• 1:10:19
  Speaker 1: paleontologist John Ostrom helped revive the dinosaur origin of birds
• 1:10:24
  Speaker 1: through his work on Deinonychus. Deinonychus was a relatively small,
• 1:10:29
  Speaker 1: agile theropod with powerful hind limbs, grasping forelimbs and a
• 1:10:34
  Speaker 1: large curved claw on each foot. Its skeleton showed striking
• 1:10:38
  Speaker 1: similarities to Archaeopteryx and other bird-like dinosaurs. The old picture
• 1:10:43
  Speaker 1: of dinosaurs as slow, lumbering reptiles became harder to maintain. Instead,
• 1:10:49
  Speaker 1: many theropods began to look increasingly active, lightweight and bird-like.
• 1:10:54
  Speaker 1: Modern paleontology now places birds firmly within theropoda. That means
• 1:10:59
  Speaker 1: birds are not merely descended from dinosaurs in a vague sense.
• 1:11:03
  Speaker 1: Birds are dinosaurs. More specifically, they are the surviving members
• 1:11:08
  Speaker 1: of one branch of theropod dinosaurs. The evolutionary transition happened gradually.
• 1:11:14
  Speaker 1: There was no single moment when a fully dinosaur-like animal
• 1:11:17
  Speaker 1: suddenly produced a fully modern bird. Bird-like characteristics accumulated step
• 1:11:23
  Speaker 1: by step. Feathers appeared before flight. Wishbones appeared in non-bird theropods.
• 1:11:30
  Speaker 1: Skeletons became lighter. Forelimbs became more specialised. Hands changed. Tails
• 1:11:38
  Speaker 1: shortened in some lineages. Respiratory systems became increasingly sophisticated. Each
• 1:11:44
  Speaker 1: feature existed within an evolving body plan long before the
• 1:11:48
  Speaker 1: complete modern bird form appeared. Flight itself probably emerged through
• 1:11:53
  Speaker 1: a long sequence of intermediate stages. Scientists have debated whether
• 1:11:57
  Speaker 1: the ancestors of flying birds first launched themselves from the ground,
• 1:12:01
  Speaker 1: or whether climbing and gliding from elevated positions played a
• 1:12:04
  Speaker 1: major role. Different feathered theropods may have experimented with different
• 1:12:09
  Speaker 1: forms of aerial movement. Some could probably glide. Others may
• 1:12:13
  Speaker 1: have used feathered forelimbs for balance, display or assisted movement
• 1:12:18
  Speaker 1: before true powered flight evolved. And flight may not have
• 1:12:23
  Speaker 1: been a one-time experiment. Several closely related feathered dinosaur lineages
• 1:12:28
  Speaker 1: appear to have developed some degree of aerodynamic ability independently.
• 1:12:33
  Speaker 1: Evolution often works this way. Structures that first serve one
• 1:12:37
  Speaker 1: purpose can later be modified for something quite different. A
• 1:12:41
  Speaker 1: feather that begins as insulation can eventually become part of
• 1:12:44
  Speaker 1: a wing. A forelimb used for grasping can gradually become
• 1:12:48
  Speaker 1: adapted for flight. A lightweight skeleton useful for active movement
• 1:12:53
  Speaker 1: can become equally useful in the air. Once the dinosaur
• 1:12:57
  Speaker 1: origin of birds is understood, the prehistoric world begins to
• 1:13:01
  Speaker 1: look different. Feathers are no longer a peculiar bird invention
• 1:13:05
  Speaker 1: appearing after the age of dinosaurs. Brooding behaviour is no
• 1:13:09
  Speaker 1: longer uniquely avian. Wishbones, air sacs, nesting behaviour and many
• 1:13:16
  Speaker 1: aspects of movement have much deeper roots. The boundary between
• 1:13:20
  Speaker 1: dinosaur and bird becomes less like a wall and more
• 1:13:23
  Speaker 1: like a long evolutionary gradient. And that changes the meaning
• 1:13:27
  Speaker 1: of dinosaur extinction as well. When the Great Extinction came
• 1:13:31
  Speaker 1: at the end of the Cretaceous, One branch of dinosaurs survived.
• 1:13:35
  Speaker 1: Its descendants are still around us. They sit on rooftops.
• 1:13:39
  Speaker 1: They cross oceans. They build nests, brood eggs and fill
• 1:13:43
  Speaker 1: forests with sound. Every living bird carries part of a
• 1:13:47
  Speaker 1: dinosaur body plan that began evolving more than 150 million
• 1:13:51
  Speaker 1: years ago. The age of dinosaurs, in that sense, never
• 1:13:54
  Speaker 1: completely ended. Around 145 million years ago, the Jurassic period
• 1:14:00
  Speaker 1: gave way to the Cretaceous. Because the Cretaceous ends with
• 1:14:03
  Speaker 1: the most famous extinction in Earth's history, it can sometimes
• 1:14:07
  Speaker 1: feel like little more than the final act of the
• 1:14:09
  Speaker 1: dinosaur story. In reality, it lasted for almost 80 million years.
• 1:14:14
  Speaker 1: That is an extraordinary length of time. Entire mountain ranges
• 1:14:18
  Speaker 1: could rise and erode. Oceans could widen. Species could appear,
• 1:14:23
  Speaker 1: diversify and vanish while still being separated from the final
• 1:14:27
  Speaker 1: extinction by tens of millions of years. And throughout much
• 1:14:31
  Speaker 1: of that interval, dinosaurs, continued to flourish. The planet itself
• 1:14:37
  Speaker 1: was becoming increasingly recognisable. Pangaea had already begun breaking apart
• 1:14:42
  Speaker 1: during the Jurassic, but the process continued through the Cretaceous.
• 1:14:46
  Speaker 1: The Atlantic Ocean widened as the Americas moved farther away
• 1:14:49
  Speaker 1: from Africa and Europe. Gondwana fragmented into separate landmasses, and
• 1:14:54
  Speaker 1: India began a long journey northward that would eventually bring
• 1:14:57
  Speaker 1: it into collision with Asia. Continents that had once been
• 1:15:01
  Speaker 1: connected were becoming increasingly isolated. For dinosaur evolution, that isolation mattered.
• 1:15:08
  Speaker 1: Populations separated by oceans and other geographic barriers could no
• 1:15:12
  Speaker 1: longer mix freely. Over enough time, they followed their own
• 1:15:17
  Speaker 1: evolutionary paths. Different parts of the world therefore developed increasingly
• 1:15:22
  Speaker 1: distinctive dinosaur communities. This phenomenon is sometimes called geographic provincialism.
• 1:15:29
  Speaker 1: rather than one globally uniform dinosaur fauna, the Cretaceous contained
• 1:15:34
  Speaker 1: many regional combinations of animals. Tyrannosaurs became important large predators
• 1:15:39
  Speaker 1: across parts of the northern hemisphere. In southern continents, abelosaurs
• 1:15:43
  Speaker 1: occupied prominent predatory roles. Titanosaurs spread widely and included many
• 1:15:49
  Speaker 1: of the dominant long-necked herbivores. Hadrosaurs became highly successful in
• 1:15:54
  Speaker 1: parts of the northern hemisphere. while Ceratopsians eventually produced some
• 1:15:59
  Speaker 1: of the most heavily built herbivores of late Cretaceous North
• 1:16:03
  Speaker 1: America and Asia. Continental drift was helping evolution create regional worlds.
• 1:16:09
  Speaker 1: Climate was changing as well. Much of the Cretaceous experienced
• 1:16:14
  Speaker 1: what scientists describe as greenhouse conditions. Average global temperatures were
• 1:16:19
  Speaker 1: generally higher than today, and permanent ice sheets were either
• 1:16:23
  Speaker 1: greatly reduced or absent for much of the period. sea
• 1:16:26
  Speaker 1: levels also became exceptionally high. At certain times, seawater flooded
• 1:16:31
  Speaker 1: low-lying portions of the continents and created extensive shallow inland seas.
• 1:16:37
  Speaker 1: North America provides a particularly dramatic example. During parts of
• 1:16:42
  Speaker 1: the late Cretaceous, the western interior seaway stretched through the
• 1:16:46
  Speaker 1: middle of the continent, separating large areas of land to
• 1:16:49
  Speaker 1: the east and west. The dinosaurs living on either side
• 1:16:53
  Speaker 1: therefore inhabited regions divided by a vast body of water.
• 1:16:58
  Speaker 1: Warm temperatures did not mean every part of the planet
• 1:17:00
  Speaker 1: was tropical. Cretaceous dinosaurs lived across an enormous range of environments.
• 1:17:07
  Speaker 1: Fossils have been discovered at surprisingly high latitudes, including areas
• 1:17:11
  Speaker 1: within the ancient polar regions. These places could still experience
• 1:17:16
  Speaker 1: long periods of darkness during winter because Earth's axial tilt
• 1:17:20
  Speaker 1: continued to produce strong seasonal changes in daylight. A polar
• 1:17:25
  Speaker 1: dinosaur might therefore live through months when the sun barely rose,
• 1:17:29
  Speaker 1: even though average temperatures were considerably warmer than those of
• 1:17:33
  Speaker 1: modern Antarctica. The vegetation around dinosaurs was changing too. One
• 1:17:38
  Speaker 1: of the most important botanical developments was the expansion of
• 1:17:41
  Speaker 1: flowering plants, known as angiosperms. Flowering plants had appeared by
• 1:17:47
  Speaker 1: the early Cretaceous and became increasingly diverse and widespread as
• 1:17:51
  Speaker 1: the period continued, but they did not suddenly replace all
• 1:17:55
  Speaker 1: older vegetation. Conifers remained important. Ferns continued to flourish. Cycads
• 1:18:02
  Speaker 1: and other established plant groups remained parts of terrestrial ecosystems.
• 1:18:06
  Speaker 1: The Cretaceous landscape was therefore a mixture of ancient plant
• 1:18:10
  Speaker 1: communities and increasingly influential flowering plants. That change affected much
• 1:18:16
  Speaker 1: more than scenery. Plants form the base of most terrestrial
• 1:18:20
  Speaker 1: food webs. As plant communities changed, the resources available to
• 1:18:25
  Speaker 1: herbivores changed with them. Insects also diversified alongside flowering plants,
• 1:18:31
  Speaker 1: particularly groups involved in pollination and feeding on plant tissues.
• 1:18:36
  Speaker 1: These interactions created new ecological relationships across terrestrial ecosystems. it
• 1:18:42
  Speaker 1: is tempting to connect the rise of particular dinosaur groups
• 1:18:45
  Speaker 1: directly to flowering plants. But the evidence does not support
• 1:18:50
  Speaker 1: a simple story in which angiosperms appeared and immediately caused
• 1:18:54
  Speaker 1: certain dinosaurs to take over. Dinosaur evolution was influenced by
• 1:18:58
  Speaker 1: many factors at once. Climate changed. Continents moved. Sea levels
• 1:19:04
  Speaker 1: rose and fell. New competitors appeared. Old groups disappeared. vegetation diversified.
• 1:19:12
  Speaker 1: The result was not one straightforward cause and effect, but
• 1:19:16
  Speaker 1: a shifting network of evolutionary pressures. Herbivorous dinosaurs responded in
• 1:19:22
  Speaker 1: different ways. Hadrosaurs developed sophisticated arrangements of teeth capable of
• 1:19:28
  Speaker 1: processing large quantities of vegetation. Ceratoptions possessed powerful beaks and
• 1:19:34
  Speaker 1: complex dental batteries. Titanosaurs continued the enormous sauropod tradition across
• 1:19:39
  Speaker 1: many southern landmasses. Smaller herbivores occupied niches that giants could not.
• 1:19:45
  Speaker 1: Predators changed alongside them. Tyrannosaurs eventually produced some of the
• 1:19:50
  Speaker 1: most massive terrestrial carnivores ever known. Abelosaurs developed short, deep
• 1:19:56
  Speaker 1: skulls and extremely reduced forelimbs. Other theropods remained small, lightly
• 1:20:01
  Speaker 1: built and often feathered. Some dinosaur lineages were also becoming
• 1:20:05
  Speaker 1: increasingly bird-like. There was no sense, from the perspective of
• 1:20:09
  Speaker 1: the animals living through it, that the Cretaceous represented a
• 1:20:13
  Speaker 1: fading age. Dinosaurs were still evolving. New species continued to appear.
• 1:20:19
  Speaker 1: Old lineages diversified into remarkable new forms. Entire regional ecosystems
• 1:20:25
  Speaker 1: developed combinations of animals that had never existed before. If
• 1:20:30
  Speaker 1: anything … The Cretaceous demonstrates how misleading it can be
• 1:20:33
  Speaker 1: to view prehistoric life backwards from its ending. Knowing that
• 1:20:37
  Speaker 1: an asteroid will eventually arrive makes the period feel like
• 1:20:40
  Speaker 1: a countdown. But for almost 80 million years, there was
• 1:20:43
  Speaker 1: no countdown. There was simply life. Dinosaurs spread through forests,
• 1:20:49
  Speaker 1: river systems, coastal plains and polar environments, while continents drifted
• 1:20:53
  Speaker 1: beneath them. Flowering plants reshaped terrestrial ecosystems. Oceans widened. Climate
• 1:21:01
  Speaker 1: shifted and evolution continued, experimenting with bodies ranging from tiny
• 1:21:06
  Speaker 1: feathered animals to herbivores weighing many tonnes. The Cretaceous was
• 1:21:11
  Speaker 1: not the exhausted remains of the age of dinosaurs. It
• 1:21:14
  Speaker 1: was one of its most dynamic phases. Even relatively close
• 1:21:18
  Speaker 1: to the end, dinosaurs were still diversifying, specialising and adapting
• 1:21:23
  Speaker 1: to a planet that refused to remain still by the
• 1:21:26
  Speaker 1: Cretaceous period Dinosaurs had been evolving for well over 100
• 1:21:30
  Speaker 1: million years. That immense stretch of time had produced an
• 1:21:34
  Speaker 1: extraordinary range of body shapes, feeding strategies and ecological roles.
• 1:21:39
  Speaker 1: Some dinosaurs were enormous herbivores, others were small, agile predators.
• 1:21:45
  Speaker 1: Some carried armour, some had horns, some had elaborate crests.
• 1:21:49
  Speaker 1: Others were covered in feathers and may have been scarcely
• 1:21:52
  Speaker 1: larger than modern birds. There was no single dinosaur design.
• 1:21:56
  Speaker 1: There was instead a vast evolutionary radiation, with different groups
• 1:22:01
  Speaker 1: becoming increasingly specialised for different ways of life. Among the
• 1:22:05
  Speaker 1: most successful Cretaceous herbivores were the Hadrosaurs. Hadrosaurs are often
• 1:22:10
  Speaker 1: called duck-billed dinosaurs because of the broad shape of the
• 1:22:13
  Speaker 1: front of the skull, but that nickname can make them
• 1:22:16
  Speaker 1: sound simpler than they really were. Their mouths contained extremely
• 1:22:20
  Speaker 1: sophisticated dental batteries. Rather than relying on a single row
• 1:22:24
  Speaker 1: of teeth Hadrosaurs possessed large stacks of teeth that continually
• 1:22:29
  Speaker 1: replaced one another as older teeth wore down. This allowed
• 1:22:32
  Speaker 1: them to process tough plant material efficiently. Edmontosaurus is one
• 1:22:37
  Speaker 1: of the best known examples. It lived during the late
• 1:22:40
  Speaker 1: Cretaceous in North America and could reach lengths of around
• 1:22:43
  Speaker 1: 10 metres or more. Its jaws were capable of complex
• 1:22:46
  Speaker 1: movement and its densely packed teeth formed grinding surfaces that
• 1:22:51
  Speaker 1: could break down vegetation before swallowing. This was very different
• 1:22:55
  Speaker 1: from the feeding strategy of sauropods, which generally relied more
• 1:22:59
  Speaker 1: heavily on cropping vegetation and processing it internally. Hadrosaurs were,
• 1:23:04
  Speaker 1: in effect, highly specialised plant processing machines. Another major herbivorous
• 1:23:10
  Speaker 1: lineage produced the Ceratopsians. By the late Cretaceous, this group
• 1:23:14
  Speaker 1: included animals such as Triceratops. Triceratops combined several remarkable features
• 1:23:20
  Speaker 1: in one body. At the front of the skull was
• 1:23:22
  Speaker 1: a powerful beak suited to cutting vegetation. Behind it sat
• 1:23:27
  Speaker 1: complex batteries of teeth capable of slicing and processing plant material.
• 1:23:32
  Speaker 1: The skull itself was enormous. Two long horns projected above
• 1:23:37
  Speaker 1: the eyes, another horn sat over the nose, and a broad,
• 1:23:41
  Speaker 1: bony frill extended behind the head. The exact functions of
• 1:23:45
  Speaker 1: horns and frills probably varied. Defence was likely important. particularly
• 1:23:51
  Speaker 1: against large predators, but display, species recognition and competition between
• 1:23:57
  Speaker 1: individuals may also have played major roles. As with many
• 1:24:01
  Speaker 1: extravagant structures in living animals, there was probably more than
• 1:24:04
  Speaker 1: one purpose. Then there were the ankylosaurs. These were among
• 1:24:08
  Speaker 1: the most heavily defended dinosaurs ever to evolve. Their skin
• 1:24:12
  Speaker 1: contained bony plates known as osteoderms. These formed a kind
• 1:24:17
  Speaker 1: of natural armour over much of the body. The head
• 1:24:19
  Speaker 1: could also be heavily protected, and the animal's low, broad
• 1:24:24
  Speaker 1: shape made vulnerable areas difficult for a predator to reach.
• 1:24:28
  Speaker 1: Some Ankylosaur lineages took defence even further. They evolved massive
• 1:24:32
  Speaker 1: tail clubs. The end of the tail became reinforced by
• 1:24:36
  Speaker 1: enlarged bones, while the muscles and tendons controlling it allowed
• 1:24:40
  Speaker 1: the structure to be swung from side to side. A
• 1:24:43
  Speaker 1: large tail club striking a predator's leg could potentially cause
• 1:24:47
  Speaker 1: serious injury. it was a very different defensive strategy from
• 1:24:51
  Speaker 1: running away. Sometimes it was better to become difficult enough
• 1:24:55
  Speaker 1: to attack that the predator reconsidered the entire arrangement. Sauropods
• 1:24:59
  Speaker 1: were still thriving as well. Although they became less prominent
• 1:25:03
  Speaker 1: in some northern ecosystems, they remained widespread across many parts
• 1:25:07
  Speaker 1: of the world. Cretaceous sauropods were especially represented by titanosaurs.
• 1:25:12
  Speaker 1: This was a remarkably successful group with fossils found across
• 1:25:16
  Speaker 1: South America, Africa, Asia, Europe and other regions. Some titanosaurs
• 1:25:21
  Speaker 1: remained moderate in size, others became truly enormous. Animals such
• 1:25:26
  Speaker 1: as Argentinosaurus are among the candidates for the largest terrestrial
• 1:25:29
  Speaker 1: animals ever known, although estimating the size of incomplete skeletons
• 1:25:34
  Speaker 1: always involves uncertainty. Some of these giants may have weighed
• 1:25:38
  Speaker 1: many tens of tonnes and stretched for more than 30
• 1:25:41
  Speaker 1: metres from head to tail. While herbivores were becoming increasingly varied,
• 1:25:46
  Speaker 1: large predators were following different evolutionary paths on different continents.
• 1:25:51
  Speaker 1: In parts of the northern hemisphere, tyrannosaurs eventually became dominant
• 1:25:56
  Speaker 1: large carnivores. In many Gondwanan regions, abelosaurs occupied similar high-level
• 1:26:03
  Speaker 1: predatory roles. Abelosaurs often had deep skulls, relatively short snouts
• 1:26:10
  Speaker 1: and extremely reduced forelimbs. Earlier in the Cretaceous, Spinosaurids represented
• 1:26:16
  Speaker 1: yet another experiment in large theropod evolution. These animals possessed
• 1:26:21
  Speaker 1: elongated skulls and conical teeth, and several species show adaptations
• 1:26:26
  Speaker 1: associated with spending substantial time around aquatic environments and feeding
• 1:26:31
  Speaker 1: on fish as well as other prey. The diversity among
• 1:26:35
  Speaker 1: large predators is important. There was no one perfect way
• 1:26:39
  Speaker 1: to be a giant carnivorous dinosaur. Different lineages arrived at
• 1:26:43
  Speaker 1: different anatomical solutions. Tyrannosaurus represents one of the most specialised
• 1:26:48
  Speaker 1: late examples. It lived near the very end of the
• 1:26:51
  Speaker 1: Cretaceous in western North America. Its skull was enormous and
• 1:26:56
  Speaker 1: heavily reinforced. The jaws were deep. The teeth were thick,
• 1:27:01
  Speaker 1: robust and capable of withstanding forces that would have broken
• 1:27:05
  Speaker 1: the more blade-like teeth of many other theropods. Tyrannosaurus could
• 1:27:10
  Speaker 1: generate an exceptionally powerful bite. Its teeth were well suited
• 1:27:14
  Speaker 1: not merely to cutting flesh, but also to puncturing and
• 1:27:18
  Speaker 1: crushing bone. This was a very different feeding system from
• 1:27:22
  Speaker 1: that of Allosaurus tens of millions of years earlier. But
• 1:27:25
  Speaker 1: Tyrannosaurus should not become a stand-in for all predatory dinosaurs.
• 1:27:29
  Speaker 1: It was one highly specialised animal at the end of
• 1:27:32
  Speaker 1: a much older theropod lineage. Other predators were smaller, faster,
• 1:27:37
  Speaker 1: and built for very different prey. Dromaeosaurs included relatively small
• 1:27:42
  Speaker 1: feathered theropods with long tails, grasping hands and enlarged curved
• 1:27:47
  Speaker 1: claws on the feet. Troodontid-like theropods were generally lightly built
• 1:27:52
  Speaker 1: and possessed relatively large brains for their body size, along
• 1:27:56
  Speaker 1: with sharp teeth and large eyes in some species. Small
• 1:28:00
  Speaker 1: Ornithischian dinosaurs also remained important. These animals rarely dominate museum
• 1:28:06
  Speaker 1: halls because their skeletons do not tower overhead. Yet they
• 1:28:10
  Speaker 1: were part of the same ecosystems and occupied niches that
• 1:28:13
  Speaker 1: giant dinosaurs could not. Some were small herbivores, others may
• 1:28:18
  Speaker 1: have been more flexible feeders. The range in dinosaur body
• 1:28:22
  Speaker 1: size was therefore enormous. At one extreme stood animals weighing
• 1:28:26
  Speaker 1: many tens of tonnes, at the other were species smaller
• 1:28:30
  Speaker 1: than a modern chicken. That diversity can become difficult to
• 1:28:33
  Speaker 1: appreciate because popular culture tends to compress the entire Mesozoic era.
• 1:28:38
  Speaker 1: into one imaginary landscape. Stegosaurus is often shown beside Tyrannosaurus.
• 1:28:44
  Speaker 1: In reality, they were separated by roughly 80 million years.
• 1:28:48
  Speaker 1: Stegosaurus lived during the late Jurassic. Tyrannosaurus appeared only near
• 1:28:53
  Speaker 1: the end of the Cretaceous. More time separated those animals
• 1:28:56
  Speaker 1: than separates Tyrannosaurus from the modern world. Triceratops, by contrast,
• 1:29:02
  Speaker 1: really did live alongside Tyrannosaurus in late Cretaceous North America.
• 1:29:06
  Speaker 1: Geological time is simply so enormous that animals we casually
• 1:29:10
  Speaker 1: call dinosaurs can belong to worlds separated. By tens of
• 1:29:15
  Speaker 1: millions of years. By the later Cretaceous, more than 100
• 1:29:19
  Speaker 1: million years of dinosaur evolution had produced an astonishing variety
• 1:29:24
  Speaker 1: of solutions to the basic problems of survival. Some animals
• 1:29:29
  Speaker 1: processed plants with batteries of hundreds of teeth. Some defended
• 1:29:33
  Speaker 1: themselves with horns. Others carried armour or tail clubs. Some
• 1:29:38
  Speaker 1: reached sizes unmatched by any later land animal. Predators evolved
• 1:29:43
  Speaker 1: skulls and teeth suited to very different ways of feeding.
• 1:29:47
  Speaker 1: And beneath the giants lived countless smaller dinosaurs that were
• 1:29:51
  Speaker 1: every bit as much a part of the story. The
• 1:29:54
  Speaker 1: dinosaur world had not settled on one successful form. it
• 1:29:58
  Speaker 1: had done the opposite. It had diversified into almost every
• 1:30:02
  Speaker 1: available terrestrial niche, producing one of the richest and most
• 1:30:06
  Speaker 1: varied vertebrate radiations Earth had ever seen. By the final
• 1:30:11
  Speaker 1: several million years of the Cretaceous, dinosaur ecosystems were still active,
• 1:30:16
  Speaker 1: complex and deeply established. The animals living through those last
• 1:30:21
  Speaker 1: generations did not inhabit a world that looked obviously doomed.
• 1:30:25
  Speaker 1: They fed. They reproduced. They migrated through landscapes where conditions
• 1:30:31
  Speaker 1: allowed it. Predators hunted. Herbivores browsed and grazed on available vegetation.
• 1:30:38
  Speaker 1: Young animals grew toward adulthood. New individuals were born into
• 1:30:42
  Speaker 1: ecosystems that, from their perspective, were simply continuing. One of
• 1:30:48
  Speaker 1: the clearest windows into this late dinosaur world comes from
• 1:30:51
  Speaker 1: the Hell Creek formation of western North America. The rocks
• 1:30:56
  Speaker 1: of Hell Creek preserve environments from very near the end
• 1:30:59
  Speaker 1: of the Cretaceous, around 66 million years ago. They contain
• 1:31:04
  Speaker 1: river deposits, floodplain sediments and other evidence of landscapes crossed
• 1:31:09
  Speaker 1: by waterways and covered in vegetation. This was not an
• 1:31:14
  Speaker 1: open desert filled with isolated skeletons. It was a living ecosystem.
• 1:31:20
  Speaker 1: Among its most famous inhabitants was Tyrannosaurus. The same landscapes
• 1:31:24
  Speaker 1: also supported Triceratops, Edmontosaurus, Ankylosaurus and numerous smaller dinosaurs. These
• 1:31:33
  Speaker 1: animals occupied very different ecological roles. Triceratops was a heavily
• 1:31:38
  Speaker 1: built herbivore equipped with a powerful beak, horns and a
• 1:31:42
  Speaker 1: broad frill. Edmontosaurus was a large hadrosaur with sophisticated dental
• 1:31:47
  Speaker 1: batteries for processing vegetation. Ankylosaurus carried extensive body armour and
• 1:31:52
  Speaker 1: a massive tail club. Tyrannosaurus occupied the role of an
• 1:31:56
  Speaker 1: enormous predator and scavenger. But even these familiar animals represented
• 1:32:01
  Speaker 1: only a portion of the ecosystem. Birds lived there too.
• 1:32:06
  Speaker 1: So did mammals. Turtles moved through rivers and wetlands. Crocodilian
• 1:32:11
  Speaker 1: relatives occupied waterways and shorelines. Fish, amphibians and insects were everywhere.
• 1:32:18
  Speaker 1: Plants formed the base of the terrestrial food web, supporting
• 1:32:22
  Speaker 1: herbivores that in turn supported predators and scavengers. The final
• 1:32:27
  Speaker 1: dinosaur ecosystems were therefore not dinosaur-only worlds. They were intricate
• 1:32:32
  Speaker 1: biological communities containing thousands of interacting species. Hell Creek is
• 1:32:38
  Speaker 1: especially useful because it is relatively well studied. But it
• 1:32:42
  Speaker 1: represents one part of one continent. That matters. the last
• 1:32:47
  Speaker 1: dinosaurs were living across multiple regions of the planet, and
• 1:32:50
  Speaker 1: those regions did not all contain the same species. What
• 1:32:55
  Speaker 1: was happening in western North America cannot automatically be assumed
• 1:32:59
  Speaker 1: to describe conditions in South America, Asia, Europe, Africa or India.
• 1:33:04
  Speaker 1: This becomes important when paleontologists ask whether dinosaurs were already
• 1:33:09
  Speaker 1: declining before the final extinction. The answer is complicated. Some
• 1:33:14
  Speaker 1: studies suggest that certain dinosaur groups became less diverse during
• 1:33:18
  Speaker 1: the closing millions of years of the Cretaceous. In some regions,
• 1:33:22
  Speaker 1: particular lineages appear to have declined in the number of
• 1:33:25
  Speaker 1: species represented in the fossil record. Climate was changing, sea
• 1:33:30
  Speaker 1: levels were changing, habitats were shifting, continents were continuing to move.
• 1:33:36
  Speaker 1: All of these factors could influence dinosaur populations. But there
• 1:33:40
  Speaker 1: is a major problem. The fossil record is incomplete. Fossilisation
• 1:33:45
  Speaker 1: is rare. An animal must die in circumstances that allow
• 1:33:49
  Speaker 1: its remains to be buried and preserved. Those rocks must
• 1:33:53
  Speaker 1: then survive millions of years of geological change. And finally,
• 1:33:58
  Speaker 1: they must become exposed somewhere that scientists can actually find
• 1:34:02
  Speaker 1: and study them. This means some environments leave much richer
• 1:34:06
  Speaker 1: fossil records than others. Some periods are represented by abundant
• 1:34:10
  Speaker 1: rock formations. Others are barely preserved at all. A drop
• 1:34:15
  Speaker 1: in the number of known dinosaur species can therefore reflect
• 1:34:18
  Speaker 1: a real biological decline. But it can also reflect a
• 1:34:24
  Speaker 1: decline in the amount of suitable rock available for sampling.
• 1:34:27
  Speaker 1: Separating those possibilities is difficult. There is another subtle problem
• 1:34:32
  Speaker 1: called the senior ellipse effect. The idea is quite simple.
• 1:34:36
  Speaker 1: Imagine a species that survives right up until a sudden extinction.
• 1:34:41
  Speaker 1: The final individual of that species is extremely unlikely to
• 1:34:45
  Speaker 1: become a fossil. Perhaps the last fossil we happen to
• 1:34:49
  Speaker 1: discover comes from 100,000 years earlier. If we looked only
• 1:34:53
  Speaker 1: at the fossil record, it could appear that the species
• 1:34:56
  Speaker 1: disappeared gradually before the catastrophe. In reality, it may have
• 1:35:01
  Speaker 1: survived until the very end. The incompleteness of fossilisation can
• 1:35:05
  Speaker 1: therefore smear a sudden extinction backwards through time. That does
• 1:35:09
  Speaker 1: not mean every apparent decline is an illusion. It means
• 1:35:13
  Speaker 1: paleontologists must be careful when interpreting the final appearances of species.
• 1:35:18
  Speaker 1: This is why the debate over pre-extinction dinosaur decline remains active.
• 1:35:23
  Speaker 1: Some evidence points toward reduced diversity in particular groups and places.
• 1:35:27
  Speaker 1: The other evidence suggests that dinosaur communities remain diverse and
• 1:35:32
  Speaker 1: ecologically important very close to the extinction boundary. Both can
• 1:35:37
  Speaker 1: be true at the same time. One region may experience
• 1:35:41
  Speaker 1: decline while another remains stable. One lineage may shrink while
• 1:35:45
  Speaker 1: another continues to diversify. Evolution rarely moves in perfect synchrony
• 1:35:51
  Speaker 1: across an entire planet. What the evidence does not support
• 1:35:55
  Speaker 1: is a simple picture of dinosaurs slowly fading away everywhere,
• 1:35:59
  Speaker 1: merely waiting for extinction to finish the job. Non-avian dinosaurs
• 1:36:04
  Speaker 1: were still present on multiple continents near the end of
• 1:36:06
  Speaker 1: the Cretaceous. They were still reproducing. They were still occupying
• 1:36:11
  Speaker 1: major ecological roles. Predators were still hunting herbivores. Herbivores were
• 1:36:16
  Speaker 1: still feeding on evolving plant communities. Birds and mammals were
• 1:36:20
  Speaker 1: still living alongside them. The ecosystems themselves were still functioning.
• 1:36:25
  Speaker 1: That distinction matters because it changes how we understand the
• 1:36:29
  Speaker 1: final extinction. The asteroid did not arrive in an empty
• 1:36:33
  Speaker 1: world where dinosaurs had almost entirely disappeared. It struck a
• 1:36:37
  Speaker 1: planet where non-avian dinosaurs were still widespread and biologically important.
• 1:36:43
  Speaker 1: Some groups may already have been under pressure, some ecosystems
• 1:36:46
  Speaker 1: may have been changing, but pressure is not the same
• 1:36:49
  Speaker 1: as inevitable extinction. For millions of years, dinosaurs had survived
• 1:36:54
  Speaker 1: climate shifts, changes in sea level, continental breakup and competition
• 1:36:59
  Speaker 1: with countless other organisms. There was no obvious biological rule
• 1:37:04
  Speaker 1: saying their time had simply run out. Then, close to
• 1:37:08
  Speaker 1: 66 million years ago, something fundamentally different happened. A functioning
• 1:37:14
  Speaker 1: world was about to be exposed to a catastrophe capable
• 1:37:17
  Speaker 1: of affecting nearly every ecosystem on Earth at once. By
• 1:37:21
  Speaker 1: the final stages of the Cretaceous, one of the biggest
• 1:37:24
  Speaker 1: questions is whether the dinosaurs were already in decline before
• 1:37:28
  Speaker 1: the Great Extinction arrived. The answer is not simple. Some
• 1:37:33
  Speaker 1: evidence suggests that certain dinosaur groups became less diverse in
• 1:37:37
  Speaker 1: particular regions during the final millions of years. But that
• 1:37:41
  Speaker 1: is very different from saying that dinosaurs everywhere were steadily
• 1:37:44
  Speaker 1: fading away. The late Cretaceous world was still changing. Sea
• 1:37:49
  Speaker 1: levels rose and fell, climate shifted, continents continued moving, habitats
• 1:37:56
  Speaker 1: expanded in some places and contracted in others. These changes
• 1:38:00
  Speaker 1: could affect dinosaur communities in very different ways depending on
• 1:38:04
  Speaker 1: where they lived. A coastline moving inland could flood one
• 1:38:08
  Speaker 1: habitat while creating another somewhere else. A changing climate could
• 1:38:12
  Speaker 1: reduce suitable vegetation for one group of herbivores while favouring another.
• 1:38:17
  Speaker 1: Geographic isolation could split populations and encourage new species to
• 1:38:21
  Speaker 1: form in one region, even while diversity declined elsewhere. That
• 1:38:26
  Speaker 1: makes the final Cretaceous difficult to summarise with one global trend.
• 1:38:31
  Speaker 1: Some dinosaur groups do appear to have declined in diversity
• 1:38:35
  Speaker 1: before the end. There is evidence that certain larger bivorous
• 1:38:38
  Speaker 1: lineages became less varied in some parts of North America.
• 1:38:43
  Speaker 1: Other studies have suggested broader declines among particular dinosaur branches,
• 1:38:48
  Speaker 1: but elsewhere dinosaur communities remained rich and ecologically important close
• 1:38:53
  Speaker 1: to the extinction boundary. That mixed picture matters. Evolution does
• 1:38:59
  Speaker 1: not behave like a single global population moving neatly in
• 1:39:03
  Speaker 1: one direction. Different continents can tell different stories. Different lineages
• 1:39:08
  Speaker 1: can respond differently to the same environmental pressures. One group
• 1:39:12
  Speaker 1: may be shrinking while another remains stable. A third may
• 1:39:17
  Speaker 1: even be diversifying. The fossil record makes this harder to
• 1:39:21
  Speaker 1: judge because it is uneven. To preserve a dinosaur, several
• 1:39:25
  Speaker 1: unlikely things have to happen. The animal must die in
• 1:39:28
  Speaker 1: the right environment. Its remains must be buried quickly enough
• 1:39:31
  Speaker 1: to escape complete destruction. Those sediments must later turn into rock.
• 1:39:36
  Speaker 1: The rock must survive erosion, burial and tectonic activity. Then,
• 1:39:42
  Speaker 1: millions of years later, it must become exposed somewhere that
• 1:39:45
  Speaker 1: paleontologists can actually reach. That chain of events is rare.
• 1:39:50
  Speaker 1: Some geological intervals preserve abundant dinosaur fossils. Others leave very little.
• 1:39:56
  Speaker 1: Some environments, such as floodplains and river systems, are much
• 1:40:00
  Speaker 1: better at preserving bones than upland forests or dry interiors.
• 1:40:05
  Speaker 1: And some parts of the world have been studied for
• 1:40:07
  Speaker 1: far longer and far more intensively than others. This creates
• 1:40:12
  Speaker 1: what scientists call sampling bias. If one interval contains many
• 1:40:17
  Speaker 1: fossil-bearing rock formations and another contains very few, the better
• 1:40:22
  Speaker 1: sampled interval may appear more biologically diverse, even if the
• 1:40:26
  Speaker 1: real difference was smaller. The same problem applies geographically. North
• 1:40:31
  Speaker 1: America has an exceptionally rich late Cretaceous fossil record. Other
• 1:40:36
  Speaker 1: regions are much less complete. That means global conclusions drawn
• 1:40:41
  Speaker 1: from one well-sampled area must be treated cautiously. Finding fewer
• 1:40:47
  Speaker 1: species in the youngest layers does not automatically prove that
• 1:40:50
  Speaker 1: the animals were disappearing everywhere. Sometimes it may reflect a
• 1:40:54
  Speaker 1: real decline. Sometimes it may reflect missing rock. Often, scientists
• 1:41:00
  Speaker 1: have to work out how much of the signal comes
• 1:41:02
  Speaker 1: from biology and how much comes from geology. This distinction
• 1:41:07
  Speaker 1: becomes especially important near the end of the Cretaceous. If
• 1:41:11
  Speaker 1: the fossil record becomes patchier toward the extinction boundary, then
• 1:41:15
  Speaker 1: species may seem to vanish earlier than they actually did.
• 1:41:18
  Speaker 1: The last fossil we find from a species is almost
• 1:41:21
  Speaker 1: never the last individual that lived. There could have been
• 1:41:24
  Speaker 1: thousands of animals still alive after the youngest fossil currently known.
• 1:41:29
  Speaker 1: That is why paleontologists are careful about treating the final
• 1:41:32
  Speaker 1: appearance of a fossil as the precise moment a species disappeared.
• 1:41:38
  Speaker 1: The deeper question is whether any pre-existing decline changes the
• 1:41:42
  Speaker 1: explanation for the mass extinction. It does not have to.
• 1:41:46
  Speaker 1: A population does not need to be perfectly healthy for
• 1:41:49
  Speaker 1: a sudden catastrophe to become the decisive event that destroys it.
• 1:41:55
  Speaker 1: Several pressures can act at the same time. Climate change
• 1:41:58
  Speaker 1: can weaken ecosystems. Sea level changes can reduce habitat. Volcanism
• 1:42:04
  Speaker 1: can alter temperature and atmospheric chemistry. Competition and ordinary evolutionary
• 1:42:10
  Speaker 1: turnover can remove individual species. Then an external catastrophe can
• 1:42:15
  Speaker 1: arrive and push already stressed systems beyond the point of recovery.
• 1:42:20
  Speaker 1: This is the difference between background extinction and mass extinction.
• 1:42:25
  Speaker 1: Background extinction is the normal disappearance of species through geological time.
• 1:42:30
  Speaker 1: Species evolve. Environments change. Some lineages fail to adapt or
• 1:42:36
  Speaker 1: are replaced by others. This process is always happening. Mass
• 1:42:41
  Speaker 1: extinction is different. The rate of loss becomes exceptionally high.
• 1:42:45
  Speaker 1: Extinction affects many unrelated groups across broad geographic areas and
• 1:42:50
  Speaker 1: multiple environments. The scale and speed of biological loss rise
• 1:42:55
  Speaker 1: far beyond the ordinary background level. The end of the
• 1:42:59
  Speaker 1: Cretaceous clearly falls into that second category. The extinction did
• 1:43:03
  Speaker 1: not remove only one dinosaur lineage. It eliminated every known
• 1:43:08
  Speaker 1: non-avian dinosaur. Many marine organisms disappeared as well. Pterosaurs vanished.
• 1:43:14
  Speaker 1: Ammonites disappeared. Major groups of marine reptiles were lost. The
• 1:43:19
  Speaker 1: crisis spread across both land and sea. That scale is
• 1:43:23
  Speaker 1: difficult to explain through gradual dinosaur decline alone. Even if
• 1:43:28
  Speaker 1: some groups were already under pressure, many non-avian dinosaurs were
• 1:43:32
  Speaker 1: still alive and ecologically significant immediately before the extinction. Tyrannosaurs
• 1:43:37
  Speaker 1: still occupied major predatory roles. Ceratopsians and hadrosaurs remained important herbivores.
• 1:43:45
  Speaker 1: Titanosaurs were still widespread in several parts of the world.
• 1:43:49
  Speaker 1: Smaller dinosaurs continued filling a variety of ecological niches. These
• 1:43:54
  Speaker 1: were not ghost populations clinging to existence in empty landscapes.
• 1:43:59
  Speaker 1: They were components of functioning ecosystems. The debate over pre-extinction
• 1:44:04
  Speaker 1: decline is therefore not really a choice between two extremes.
• 1:44:08
  Speaker 1: it is not necessary to argue that dinosaurs were either
• 1:44:11
  Speaker 1: perfectly healthy everywhere, or already. Doomed everywhere. The evidence points
• 1:44:17
  Speaker 1: toward a more complicated reality. Some regions and lineages were changing,
• 1:44:23
  Speaker 1: some may have been declining, others remained diverse, and all
• 1:44:27
  Speaker 1: of them lived on a planet that was already dynamic
• 1:44:30
  Speaker 1: and sometimes unstable. Then something happened that was different in scale.
• 1:44:35
  Speaker 1: The final extinction required more than the ordinary passage of
• 1:44:39
  Speaker 1: geological time. It required a disruption capable of reaching across continents,
• 1:44:45
  Speaker 1: oceans and food webs. Whatever pressures dinosaurs were already facing,
• 1:44:50
  Speaker 1: they had survived environmental change for more than 160 million years.
• 1:44:55
  Speaker 1: Their ending would take something far more abrupt. In the
• 1:44:59
  Speaker 1: final stages of the Cretaceous, another major force was reshaping
• 1:45:03
  Speaker 1: the planet. This time, the source was deep inside the earth.
• 1:45:08
  Speaker 1: Across what is now India, enormous volcanic eruptions produced a
• 1:45:12
  Speaker 1: region known today as the Deccan Traps. The word traps
• 1:45:16
  Speaker 1: comes from a term for steps, referring to the stair-like
• 1:45:20
  Speaker 1: landscapes formed by layer upon layer of hardened lava. These
• 1:45:25
  Speaker 1: eruptions created one of the largest volcanic provinces preserved on earth.
• 1:45:30
  Speaker 1: They did not come from a single cone-shaped volcano erupting
• 1:45:33
  Speaker 1: on one catastrophic afternoon. Instead, volcanism occurred in repeated pulses
• 1:45:39
  Speaker 1: over a substantial interval around the end of the Cretaceous.
• 1:45:43
  Speaker 1: Huge volumes of basaltic lava spread across the landscape. Some
• 1:45:48
  Speaker 1: individual flows extended for great distances. Over time, the accumulated
• 1:45:54
  Speaker 1: lava covered an enormous area. But … As with the
• 1:45:58
  Speaker 1: volcanic crisis near the end of the Triassic, the lava
• 1:46:01
  Speaker 1: itself was only part of the environmental story. The gases
• 1:46:05
  Speaker 1: released during these eruptions may have had effects far beyond India.
• 1:46:10
  Speaker 1: Carbon dioxide was one of the most important. Large volcanic
• 1:46:15
  Speaker 1: provinces can inject vast quantities of carbon dioxide into the atmosphere.
• 1:46:20
  Speaker 1: Because carbon dioxide traps heat, Sustained volcanic emissions can contribute
• 1:46:26
  Speaker 1: to longer-term global warming. That warming can alter rainfall patterns,
• 1:46:31
  Speaker 1: ocean circulation and the distribution of habitats. It can also
• 1:46:36
  Speaker 1: place additional stress on ecosystems already adjusting to other environmental changes.
• 1:46:41
  Speaker 1: Sulphur-bearing gases created a different problem. When sulphur dioxide reaches
• 1:46:47
  Speaker 1: the atmosphere, it can contribute to the formation of tiny
• 1:46:50
  Speaker 1: sulphate aerosols. These particles reflect some incoming sunlight back into space.
• 1:46:56
  Speaker 1: The result can be cooling over shorter periods. So the
• 1:46:59
  Speaker 1: climatic effects of intense volcanism are not necessarily simple. The
• 1:47:04
  Speaker 1: same eruptive episode can contribute to longer-term warming through carbon
• 1:47:08
  Speaker 1: dioxide and shorter-term cooling through sulphur aerosols. Repeated eruptions can
• 1:47:14
  Speaker 1: therefore push climate in different directions over different timescales. There
• 1:47:18
  Speaker 1: are also consequences for oceans. Carbon dioxide dissolving into seawater
• 1:47:23
  Speaker 1: can contribute to ocean acidification. Changes in temperature can affect
• 1:47:28
  Speaker 1: how much oxygen seawater holds. Altered circulation can further disturb
• 1:47:33
  Speaker 1: marine environments, and sulphur compounds can contribute to acid rain
• 1:47:37
  Speaker 1: and chemical stress on both land and in the oceans.
• 1:47:41
  Speaker 1: By the latest Cretaceous, marine ecosystems were already showing signs
• 1:47:46
  Speaker 1: of environmental change. Some groups were declining. Ocean temperatures and
• 1:47:51
  Speaker 1: chemistry were shifting. Sea levels had also changed substantially from
• 1:47:55
  Speaker 1: earlier Cretaceous highs. The planet was not environmentally static. That
• 1:48:00
  Speaker 1: makes the Deccan Traps an important part of the extinction story.
• 1:48:04
  Speaker 1: Scientists have spent decades trying to determine exactly when the
• 1:48:08
  Speaker 1: largest volcanic pulses occurred relative to the final mass extinction.
• 1:48:13
  Speaker 1: This is a difficult problem because geological events separated by
• 1:48:17
  Speaker 1: tens of thousands of years can appear almost simultaneous when
• 1:48:21
  Speaker 1: viewed across 66 million years of deep time. Modern dating
• 1:48:25
  Speaker 1: techniques have become precise enough to narrow the timing considerably.
• 1:48:30
  Speaker 1: Researchers compare radiometric ages from lava flows, sedimentary layers and
• 1:48:36
  Speaker 1: the extinction boundary itself. They also study changes in climate
• 1:48:40
  Speaker 1: and ocean chemistry, preserved in rocks and fossils. The central
• 1:48:45
  Speaker 1: question is straightforward. How much of the environmental disruption happened
• 1:48:50
  Speaker 1: before the asteroid impact, and how much happened after it?
• 1:48:54
  Speaker 1: That timing matters because cause and effect depend on sequence.
• 1:48:58
  Speaker 1: If a major volcanic pulse occurred well before the impact,
• 1:49:02
  Speaker 1: it could have placed ecosystems under stress before the final catastrophe.
• 1:49:07
  Speaker 1: If substantial eruptions followed the impact, they may have influenced
• 1:49:10
  Speaker 1: the recovery. And if major eruptive phases overlapped the extinction
• 1:49:16
  Speaker 1: interval closely, then both processes may have contributed in different ways.
• 1:49:21
  Speaker 1: This is why the extinction is not best understood as
• 1:49:24
  Speaker 1: a contest between volcanism and asteroid impact, with only one
• 1:49:28
  Speaker 1: allowed to matter. Nature does not organise disasters for the
• 1:49:32
  Speaker 1: convenience of simple explanations. Several environmental pressures can operate at once.
• 1:49:38
  Speaker 1: The Deccan eruptions may have altered climate, ocean chemistry and
• 1:49:41
  Speaker 1: habitats over a prolonged period. That does not mean they
• 1:49:45
  Speaker 1: were necessarily the principal cause of the abrupt and cretaceous
• 1:49:48
  Speaker 1: mass extinction. The strongest evidence for the sudden global crisis
• 1:49:52
  Speaker 1: points toward the Chicxulub asteroid impact. The timing of that
• 1:49:56
  Speaker 1: impact aligns with the extinction boundary. A distinctive layer of
• 1:50:00
  Speaker 1: material associated with the collision appears around the world. The
• 1:50:04
  Speaker 1: impact produced exactly the kind of rapid, planetary-scale disruption capable
• 1:50:09
  Speaker 1: of collapsing food webs across land and sea. The pattern
• 1:50:12
  Speaker 1: of extinction also fits a sudden reduction in sunlight and
• 1:50:16
  Speaker 1: primary productivity. Volcanism remains important because it describes the environmental
• 1:50:21
  Speaker 1: background into which the impact arrived. Some ecosystems may already
• 1:50:25
  Speaker 1: have been experiencing stress. Temperatures had fluctuated. Ocean chemistry had changed.
• 1:50:32
  Speaker 1: Habitats had shifted. Species were responding to conditions that were
• 1:50:36
  Speaker 1: not perfectly stable. But none of this means the dinosaurs
• 1:50:39
  Speaker 1: were somehow waiting for an asteroid. There was no warning
• 1:50:42
  Speaker 1: visible in the sky. No animal could know that a
• 1:50:46
  Speaker 1: large object was travelling through space on a collision course
• 1:50:48
  Speaker 1: with Earth. The decan eruptions and the incoming asteroid were
• 1:50:52
  Speaker 1: separate phenomena produced by completely different processes. One came from
• 1:50:57
  Speaker 1: the deep interior of the planet. The other came from
• 1:51:00
  Speaker 1: beyond it. From the perspective of a dinosaur living thousands
• 1:51:04
  Speaker 1: of kilometres from India, volcanic changes might have been experienced
• 1:51:07
  Speaker 1: only indirectly. A shift in temperature, a change in rainfall,
• 1:51:13
  Speaker 1: different vegetation, perhaps a difficult season. Life would still continue.
• 1:51:19
  Speaker 1: Animals would feed and reproduce. Predators would hunt. Herds would
• 1:51:24
  Speaker 1: move through familiar landscapes. The world might have been changing,
• 1:51:28
  Speaker 1: but change itself was nothing new. Dinosaurs had lived through
• 1:51:31
  Speaker 1: enormous climatic and geological transformations before. They had survived the
• 1:51:36
  Speaker 1: breakup of continents, changing sea levels and previous episodes of volcanism.
• 1:51:42
  Speaker 1: There was no reason for any creature alive at the
• 1:51:44
  Speaker 1: time to treat these environmental pressures as the beginning of
• 1:51:47
  Speaker 1: the end. That is what makes the final crisis so different.
• 1:51:52
  Speaker 1: The Deccan Traps remind us that extinction did not occur
• 1:51:55
  Speaker 1: against a perfectly calm background. Earth was already geologically active.
• 1:52:00
  Speaker 1: Climate and ecosystems were already shifting. Volcanism may have added
• 1:52:05
  Speaker 1: meaningful stress to that changing world, but the event that
• 1:52:08
  Speaker 1: followed was much faster and far more sudden. A disturbance
• 1:52:13
  Speaker 1: that had begun deep beneath the Earth's surface was about
• 1:52:16
  Speaker 1: to be overshadowed by one arriving from space. 66 million
• 1:52:20
  Speaker 1: years ago, an asteroid roughly 10 to 15 kilometres across
• 1:52:24
  Speaker 1: was moving towards the Earth. At first, it would have
• 1:52:27
  Speaker 1: been just another object travelling through the solar system. then
• 1:52:30
  Speaker 1: its path intersected with ours. It struck near what is
• 1:52:34
  Speaker 1: now the Yucatan Peninsula of Mexico, releasing an amount of
• 1:52:38
  Speaker 1: energy almost impossible to picture on a human scale. The
• 1:52:41
  Speaker 1: scar left behind is known as the Chicxulub crater. Today,
• 1:52:45
  Speaker 1: most of it is buried beneath younger sediments and partly
• 1:52:49
  Speaker 1: beneath the Gulf of Mexico, so there is no enormous
• 1:52:52
  Speaker 1: open hole waiting to be seen from the ground. Yet
• 1:52:55
  Speaker 1: geophysical surveys reveal a vast circular structure roughly 150 to
• 1:53:01
  Speaker 1: 200 kilometres across. Drilling has recovered rocks that were fractured,
• 1:53:05
  Speaker 1: melted and transformed by tremendous pressures. Minerals within the impact
• 1:53:10
  Speaker 1: structure preserve microscopic evidence of shock conditions that ordinary geological
• 1:53:15
  Speaker 1: processes do not produce. The crater also dates to the
• 1:53:19
  Speaker 1: same interval as the encretaceous mass extinction. The connection between
• 1:53:23
  Speaker 1: an asteroid and the disappearance of the dinosaurs, however, was
• 1:53:26
  Speaker 1: not obvious for most of scientific history. One of the
• 1:53:30
  Speaker 1: crucial discoveries came from a thin layer of rock, marking
• 1:53:33
  Speaker 1: the boundary between the Cretaceous and the geological period that followed.
• 1:53:38
  Speaker 1: Geologist Walter Alvarez was studying this boundary in Italy when
• 1:53:41
  Speaker 1: attention turned to an unusual chemical signature within it. Working
• 1:53:46
  Speaker 1: with his father, physicist Luis Alvarez, and other researchers, the
• 1:53:50
  Speaker 1: team measured unexpectedly high concentrations of the element iridium. In 1980,
• 1:53:56
  Speaker 1: they proposed a remarkable explanation. A large extraterrestrial object had
• 1:54:01
  Speaker 1: struck the Earth at the end of the Cretaceous and
• 1:54:04
  Speaker 1: triggered the mass extinction. Iridium was central to their argument.
• 1:54:08
  Speaker 1: The element is relatively scarce in the Earth's crust. Much
• 1:54:12
  Speaker 1: of the planet's original iridium sank deeper into the Earth
• 1:54:15
  Speaker 1: during its early history because it tends to associate with
• 1:54:18
  Speaker 1: metallic material. Many meteorites, however, contain considerably more iridium than
• 1:54:24
  Speaker 1: ordinary crustal rocks. Finding an iridium-rich layer at the extinction
• 1:54:29
  Speaker 1: boundary was therefore difficult to explain through everyday sedimentation. More importantly,
• 1:54:35
  Speaker 1: similar enrichment was eventually identified at locations around the world.
• 1:54:40
  Speaker 1: Whatever had happened was not merely local. Material had been
• 1:54:43
  Speaker 1: distributed across the planet. The Chicxulub crater provided the missing
• 1:54:48
  Speaker 1: impact site. When the asteroid arrived, it was travelling at
• 1:54:51
  Speaker 1: many kilometres every second. At those velocities, An impact is
• 1:54:56
  Speaker 1: not remotely comparable to a large rock simply hitting the ground.
• 1:55:00
  Speaker 1: The kinetic energy becomes an enormous explosive release. In moments,
• 1:55:06
  Speaker 1: rock at the impact site was crushed, melted and vaporised.
• 1:55:10
  Speaker 1: A cavity tens of kilometres deep formed temporarily before the
• 1:55:14
  Speaker 1: surrounding crust collapsed and rebounded. The crater itself developed in minutes.
• 1:55:20
  Speaker 1: The energy released was equivalent to many millions of the
• 1:55:23
  Speaker 1: largest human-made explosions. the surrounding region would have been devastated
• 1:55:28
  Speaker 1: almost instantly. Violent seismic waves travelled outward through the crust.
• 1:55:33
  Speaker 1: Earthquakes on a scale far beyond familiar modern events shook
• 1:55:37
  Speaker 1: enormous areas. Material from the impact site was hurled upwards
• 1:55:41
  Speaker 1: at tremendous speeds. Some remained within the atmosphere. Some travelled
• 1:55:46
  Speaker 1: enormous distances. Some was launched on trajectories that carried it
• 1:55:51
  Speaker 1: beyond the atmosphere before it eventually fell back towards the Earth.
• 1:55:55
  Speaker 1: Because the impact occurred near a shallow sea, it also
• 1:55:58
  Speaker 1: displaced vast quantities of water. Immense tsunamis spread through nearby
• 1:56:03
  Speaker 1: ocean basins. Evidence of these disturbances has been preserved in
• 1:56:07
  Speaker 1: sediments deposited around the Gulf of Mexico and beyond. Close
• 1:56:12
  Speaker 1: to the impact, the destruction was overwhelming. But the extinction
• 1:56:16
  Speaker 1: of species on distant continents cannot be explained simply by
• 1:56:19
  Speaker 1: the crater, earthquakes and tsunamis. The most important consequences became global.
• 1:56:26
  Speaker 1: The impact blasted pulverised rock, dust, gases and other material
• 1:56:31
  Speaker 1: high into the atmosphere. Some of the ejected rock had
• 1:56:35
  Speaker 1: been heated sufficiently to melt. As molten droplets cooled, they
• 1:56:39
  Speaker 1: formed tiny glassy particles that fell back across large regions.
• 1:56:44
  Speaker 1: Re-entering ejecta also transferred heat into the atmosphere. This contributed
• 1:56:49
  Speaker 1: to intense thermal conditions and widespread fires. There is evidence
• 1:56:54
  Speaker 1: for substantial burning at the end of the Cretaceous, but
• 1:56:57
  Speaker 1: it is important not to turn this into an image
• 1:56:59
  Speaker 1: of every square metre of the planet bursting into flames simultaneously.
• 1:57:05
  Speaker 1: The severity of heating and fire varied geographically. Some environments
• 1:57:09
  Speaker 1: burned extensively, others experienced less direct thermal damage. The extinction
• 1:57:15
  Speaker 1: was devastating enough without adding effects the evidence does not require.
• 1:57:20
  Speaker 1: What happened after the first hours was ultimately more important
• 1:57:23
  Speaker 1: for life across the whole planet. The asteroid had struck
• 1:57:27
  Speaker 1: rocks containing large quantities of carbonate and sulphate minerals. That
• 1:57:32
  Speaker 1: location mattered enormously. The heat and violence of the impact
• 1:57:36
  Speaker 1: vaporised some of these rocks, injecting sulphur-bearing gases and immense
• 1:57:40
  Speaker 1: quantities of fine material into the atmosphere. Soot from fires
• 1:57:45
  Speaker 1: added to the darkness. Dust and aerosols spread around the globe,
• 1:57:49
  Speaker 1: sunlight reaching the surface fell dramatically. The Earth began moving
• 1:57:54
  Speaker 1: towards what scientists call an impact winter. Temperatures dropped. Photosynthesis
• 1:58:00
  Speaker 1: was severely disrupted. Plants and microscopic marine organisms that depended
• 1:58:06
  Speaker 1: on sunlight suddenly faced conditions unlike any experienced by the
• 1:58:11
  Speaker 1: ecosystems immediately beforehand. The consequences spread through food webs. On land,
• 1:58:19
  Speaker 1: herbivores ultimately depended on plants. Carnivores depended on herbivores and
• 1:58:24
  Speaker 1: smaller prey. In the oceans, countless food chains depended on
• 1:58:29
  Speaker 1: photosynthetic plankton near the surface. Remove enough sunlight and the
• 1:58:33
  Speaker 1: problem does not remain confined to plants. It moves upwards.
• 1:58:38
  Speaker 1: The largest dinosaurs were not all killed in the instant
• 1:58:41
  Speaker 1: of impact. A Tyrannosaurus, thousands of kilometres from Chicxulub, might
• 1:58:47
  Speaker 1: have survived the first day. A herd of herbivorous dinosaurs
• 1:58:51
  Speaker 1: on another continent might have avoided the earthquakes, fires and waves.
• 1:58:56
  Speaker 1: Some animals would have experienced the initial event mainly as
• 1:58:59
  Speaker 1: strange atmospheric effects, falling debris or rapidly changing weather. But
• 1:59:06
  Speaker 1: survival through the first hours did not mean safety. The
• 1:59:10
  Speaker 1: world around them was being transformed. Temperatures were changing. Vegetation
• 1:59:15
  Speaker 1: was becoming scarce. Fresh plant growth was failing. Food chains
• 1:59:21
  Speaker 1: that had operated for millions of years were beginning to break.
• 1:59:25
  Speaker 1: The distinction is important. The asteroid did not simply strike
• 1:59:28
  Speaker 1: the Earth and make every dinosaur disappear at once. It
• 1:59:33
  Speaker 1: initiated a sequence of environmental changes. The impact itself lasted moments.
• 1:59:39
  Speaker 1: The biological consequences unfolded over much longer. Some organisms died immediately.
• 1:59:46
  Speaker 1: Others survived days, months or perhaps longer, only to face
• 1:59:50
  Speaker 1: ecosystems in which familiar sources of food had vanished. And
• 1:59:55
  Speaker 1: unlike a regional disaster, there was no unaffected continent where
• 1:59:59
  Speaker 1: the old ecological system could simply continue. Material from Csikszentmihalyi
• 2:00:04
  Speaker 1: had entered the global atmosphere. Its effects reached across oceans
• 2:00:08
  Speaker 1: and hemispheres. The geological record preserves that global event in
• 2:00:13
  Speaker 1: the iridium-rich boundary layer, shocked minerals, impact ejecta, and the
• 2:00:18
  Speaker 1: enormous buried crater itself. For more than 160 million years,
• 2:00:25
  Speaker 1: Non-avian dinosaurs had survived changing climates, drifting continents, volcanic eruptions
• 2:00:32
  Speaker 1: and the ordinary rise and fall of species. Now, in
• 2:00:35
  Speaker 1: an extraordinarily brief geological instant, the conditions supporting their world
• 2:00:41
  Speaker 1: had changed. The asteroid had already struck, but the deepest
• 2:00:46
  Speaker 1: part of the extinction was only beginning. Across the planet,
• 2:00:50
  Speaker 1: daylight was fading, temperatures were falling, and the foundations of
• 2:00:54
  Speaker 1: entire food webs were starting to collapse. The asteroid impact
• 2:00:58
  Speaker 1: was over quickly. The extinction was not. Once dust, soot
• 2:01:03
  Speaker 1: and sulphur-bearing particles spread through the atmosphere, the deeper biological
• 2:01:08
  Speaker 1: crisis began to unfold. Sunlight reaching the surface dropped sharply.
• 2:01:13
  Speaker 1: That immediately threatened photosynthesis. Plants on land depended on light.
• 2:01:19
  Speaker 1: So did microscopic organisms near the surface of the oceans.
• 2:01:23
  Speaker 1: As primary productivity declined, food chains began to fail from
• 2:01:28
  Speaker 1: the bottom upward. This was the beginning of an impact winter.
• 2:01:32
  Speaker 1: Temperatures fell rapidly. Plant growth slowed or stopped in many places.
• 2:01:38
  Speaker 1: Fresh vegetation became scarce. In the oceans, photosynthetic plankton declined,
• 2:01:44
  Speaker 1: affecting animals that depended on them directly, and then the
• 2:01:47
  Speaker 1: predators that depended on those animals in turn. The damage
• 2:01:52
  Speaker 1: spread through ecosystems in layers. Large animals faced a particularly
• 2:01:56
  Speaker 1: difficult problem. A large body requires a large and regular
• 2:02:00
  Speaker 1: supply of food. That had been an advantage in the
• 2:02:04
  Speaker 1: stable ecosystems of the Cretaceous, where giant herbivores could consume
• 2:02:08
  Speaker 1: vast quantities of vegetation and giant predators could depend on
• 2:02:13
  Speaker 1: abundant prey. After the impact, that same size became a liability.
• 2:02:20
  Speaker 1: An enormous herbivore could not simply survive for long on
• 2:02:23
  Speaker 1: a handful of seeds. A giant predator could not function
• 2:02:27
  Speaker 1: if large prey populations collapsed. Specialisation made things harder still.
• 2:02:33
  Speaker 1: An animal dependent on one narrow kind of food faced
• 2:02:37
  Speaker 1: greater danger if that resource disappeared. In a stable world,
• 2:02:42
  Speaker 1: specialisation can be extremely effective. In a collapsing one, flexibility
• 2:02:47
  Speaker 1: becomes more valuable. The extinction was not confined to dinosaurs.
• 2:02:52
  Speaker 1: Every known non-avian dinosaur lineage disappeared. But they were part
• 2:02:57
  Speaker 1: of a much broader biological crisis. Pterosaurs vanished. Ammonites disappeared
• 2:03:03
  Speaker 1: from the oceans. Major groups of marine reptiles were lost.
• 2:03:08
  Speaker 1: Many species of birds, mammals, reptiles, amphibians and fish also
• 2:03:14
  Speaker 1: became extinct. Survival was not easy simply because an animal
• 2:03:18
  Speaker 1: happened to belong to a group that still exists today.
• 2:03:22
  Speaker 1: Most living lineages passed through severe evolutionary bottlenecks. Only a
• 2:03:27
  Speaker 1: fraction of the species alive before the impact survived into
• 2:03:30
  Speaker 1: the world that followed. Certain traits appear to have improved
• 2:03:34
  Speaker 1: the odds. Small body size was useful because small animals
• 2:03:38
  Speaker 1: required less food. Flexible diets helped because survivors could make
• 2:03:43
  Speaker 1: use of whatever resources remained. Burrowing may have provided shelter
• 2:03:48
  Speaker 1: from fires, temperature swings and harsh surface conditions. Freshwater habitats
• 2:03:54
  Speaker 1: may also have offered some protection, because many freshwater food
• 2:03:57
  Speaker 1: chains can depend heavily on dead, organic material rather than
• 2:04:02
  Speaker 1: immediate photosynthesis. Dormant eggs, seeds and other resting stages could
• 2:04:07
  Speaker 1: outlast conditions that killed active organisms. No single trait guaranteed survival.
• 2:04:14
  Speaker 1: Chance mattered too. Two similar species could experience very different
• 2:04:19
  Speaker 1: outcomes depending on where they lived, what resources remained nearby,
• 2:04:24
  Speaker 1: and how local conditions unfolded after the impact. This is
• 2:04:28
  Speaker 1: especially important when we look at birds. Birds were already dinosaurs.
• 2:04:33
  Speaker 1: They had evolved within Theropoda long before the extinction. So
• 2:04:37
  Speaker 1: when we say that the dinosaurs died out, the more
• 2:04:41
  Speaker 1: accurate statement is that the non-avian dinosaurs died out. avian
• 2:04:45
  Speaker 1: dinosaurs survived. That distinction changes the entire meaning of the extinction.
• 2:04:52
  Speaker 1: The dinosaur lineage did not vanish completely. One branch crossed
• 2:04:56
  Speaker 1: the boundary. But even among birds, survival was highly selective.
• 2:05:02
  Speaker 1: Many Cretaceous bird lineages disappeared. Some had teeth. Some were
• 2:05:07
  Speaker 1: strongly adapted to life in trees. Others occupied specialised ecological roles.
• 2:05:14
  Speaker 1: that became difficult to sustain after forests collapsed and food
• 2:05:18
  Speaker 1: webs were disrupted. The birds that survived appear to have
• 2:05:22
  Speaker 1: shared combinations of traits that may have been useful in
• 2:05:25
  Speaker 1: the post-impact world. Small body size was one advantage. Ground-dwelling
• 2:05:31
  Speaker 1: lifestyles may also have helped at a time when forests
• 2:05:34
  Speaker 1: were being devastated. Beaks and muscular gizzards allowed some birds
• 2:05:38
  Speaker 1: to process food without relying on teeth. Seeds may have
• 2:05:42
  Speaker 1: been particularly valuable. Unlike fresh leaves or fruit, seeds can
• 2:05:47
  Speaker 1: remain available after plants themselves have been damaged. They can
• 2:05:51
  Speaker 1: persist in soil and leaf litter. A small bird capable
• 2:05:55
  Speaker 1: of eating seeds would therefore have access to a food
• 2:05:59
  Speaker 1: source that could survive the collapse of green vegetation better
• 2:06:02
  Speaker 1: than many others. But this should not be turned into
• 2:06:06
  Speaker 1: a simple rule that seed eating saved birds. Survival probably
• 2:06:10
  Speaker 1: depended on several traits working together. Ecology mattered. Geography mattered.
• 2:06:17
  Speaker 1: Diet mattered. Body size mattered. And chance mattered. The birds
• 2:06:22
  Speaker 1: that made it through represented only a fraction of earlier
• 2:06:25
  Speaker 1: avian diversity. Yet from that reduced group came every bird
• 2:06:30
  Speaker 1: alive today. The world after the impact would have looked
• 2:06:34
  Speaker 1: drastically altered. Forests had been damaged or destroyed across large regions.
• 2:06:40
  Speaker 1: Food webs had collapsed. Many familiar Cretaceous animals were gone.
• 2:06:45
  Speaker 1: But ecosystems did not remain empty forever. Vegetation began to recover.
• 2:06:51
  Speaker 1: Ferns became especially abundant in some devastated landscapes, leaving what
• 2:06:56
  Speaker 1: paleontologists call a fern spike in the fossil record. As
• 2:07:01
  Speaker 1: plants returned, herbivorous animals had more food. As herbivores and
• 2:07:06
  Speaker 1: smaller animals recovered, predators found more prey. Food webs slowly
• 2:07:11
  Speaker 1: rebuilt themselves. The recovery did not recreate the old Cretaceous world.
• 2:07:17
  Speaker 1: It produced a new one. The disappearance of giant non-avian
• 2:07:21
  Speaker 1: dinosaurs left ecological opportunities open. Mammals began diversifying into roles
• 2:07:27
  Speaker 1: that had previously been unavailable. Birds also expanded into new
• 2:07:32
  Speaker 1: forms and environments. Over millions of years, these survivors produced
• 2:07:36
  Speaker 1: increasingly complex ecosystems Unlike those that had existed before the impact,
• 2:07:43
  Speaker 1: the extinction had removed dominant groups, but it had not
• 2:07:46
  Speaker 1: stopped evolution. Life continued reorganising itself around those that remained.
• 2:07:52
  Speaker 1: And this brings the dinosaur story to one of its
• 2:07:54
  Speaker 1: most surprising conclusions. A sparrow is a dinosaur. So is
• 2:07:59
  Speaker 1: an owl. So is a penguin. So is a chicken.
• 2:08:04
  Speaker 1: They are not merely descendants of dinosaurs in the loose
• 2:08:07
  Speaker 1: sense that mammals are descendants of ancient synapsids. They belong
• 2:08:12
  Speaker 1: within Dinosauria itself. Their skeletons still carry many of the
• 2:08:16
  Speaker 1: same inherited features. Their feathers have deep dinosaurian origins. Their
• 2:08:22
  Speaker 1: nesting behaviour, respiratory anatomy and body plan all emerged from
• 2:08:27
  Speaker 1: a lineage that began more than 200 million years ago.
• 2:08:31
  Speaker 1: The giant sauropods are gone. The horned ceratopsians are gone.
• 2:08:36
  Speaker 1: The armoured ankylosaurs and giant tyrannosaurs are gone. But the
• 2:08:41
  Speaker 1: evolutionary experiment did not end completely. One branch survived the darkness.
• 2:08:48
  Speaker 1: and from that branch came more than 11,000 living species
• 2:08:52
  Speaker 1: of birds. The age of the non-avian dinosaurs ended 66
• 2:08:57
  Speaker 1: million years ago. The age of dinosaurs, in the strict
• 2:09:01
  Speaker 1: evolutionary sense, never truly did. The story of the dinosaurs
• 2:09:05
  Speaker 1: began quietly. More than 200 million years ago in the Triassic,
• 2:09:10
  Speaker 1: they were only one branch among many archosaurs living in
• 2:09:13
  Speaker 1: a world still recovering from catastrophe. They were not dinosaurs.
• 2:09:17
  Speaker 1: yet the rulers of the land. They were comparatively small,
• 2:09:21
  Speaker 1: often lightly built, and they shared their environments with many
• 2:09:25
  Speaker 1: other successful reptile groups. Then came another great extinction near
• 2:09:29
  Speaker 1: the end of the Triassic. Many of those competitors disappeared.
• 2:09:34
  Speaker 1: The dinosaurs survived. That survival opened enormous ecological opportunities, and
• 2:09:40
  Speaker 1: across the Jurassic and Cretaceous they expanded into one of
• 2:09:43
  Speaker 1: the most remarkable evolutionary radiations in the history of life.
• 2:09:48
  Speaker 1: they became almost unimaginably varied. There were tiny feathered theropods,
• 2:09:53
  Speaker 1: there were heavily armoured ankylosaurs, there were ceratopsians with enormous skulls,
• 2:09:58
  Speaker 1: horns and frills, there were hadrosaurs with sophisticated dental batteries,
• 2:10:04
  Speaker 1: there were giant predatory theropods equipped with powerful jaws and
• 2:10:08
  Speaker 1: serrated teeth, and there were sauropods so large that no
• 2:10:12
  Speaker 1: other known land animals have ever surpassed them. Yet it
• 2:10:15
  Speaker 1: is important not to reduce dinosaurs to a parade of
• 2:10:18
  Speaker 1: extraordinary anatomy. They were animals. They hatched from eggs. They grew.
• 2:10:24
  Speaker 1: They searched for food. They avoided danger. They competed. They reproduced.
• 2:10:30
  Speaker 1: They became injured and sometimes healed. Some moved in groups.
• 2:10:35
  Speaker 1: Some cared for nests. Some displayed with feathers, horns or crests.
• 2:10:41
  Speaker 1: All of them lived within changing ecosystems. Adapting continuously as
• 2:10:46
  Speaker 1: climates shifted, continents moved and plant communities transformed around them.
• 2:10:51
  Speaker 1: Their world was never static, and neither were they. Among
• 2:10:56
  Speaker 1: theropod dinosaurs, feathers became increasingly important long before modern birds existed.
• 2:11:02
  Speaker 1: Structures that may first have helped with insulation or display
• 2:11:05
  Speaker 1: were gradually modified. Forelimbs changed. Skeletons became lighter. Respiratory systems
• 2:11:13
  Speaker 1: became more specialised. Eventually, some feathered theropods evolved powered flight.
• 2:11:18
  Speaker 1: Birds emerged from within the dinosaur family tree. That evolutionary
• 2:11:23
  Speaker 1: development turned out to be crucial. 66 million years ago,
• 2:11:28
  Speaker 1: the Shiksulub asteroid struck near what is now the Yucatan Peninsula.
• 2:11:33
  Speaker 1: The impact itself was devastating, but the deeper catastrophe came afterwards. Dust,
• 2:11:39
  Speaker 1: soot and sulphur-bearing materials spread through the atmosphere. Sunlight was reduced.
• 2:11:44
  Speaker 1: Temperatures fell, photosynthesis was disrupted, plants struggled, marine productivity declined,
• 2:11:52
  Speaker 1: and food webs began to unravel from their foundations upward.
• 2:11:57
  Speaker 1: Around the same interval, the Deccan Traps of India were
• 2:11:59
  Speaker 1: also erupting on an immense scale. Those eruptions likely affected
• 2:12:04
  Speaker 1: climate and ocean chemistry, and scientists continued to study exactly
• 2:12:09
  Speaker 1: how their timing and environmental effects interacted with the extinction.
• 2:12:13
  Speaker 1: the strongest evidence still points to the Chicxulub impact as
• 2:12:17
  Speaker 1: the dominant trigger of the sudden and cretaceous mass extinction.
• 2:12:22
  Speaker 1: The dinosaurs were not simply erased in one instant. Some
• 2:12:26
  Speaker 1: survived the first hours. Some may have lived for much longer.
• 2:12:30
  Speaker 1: But the world that had supported them was collapsing. Large-bodied
• 2:12:34
  Speaker 1: animals needed too much food. Specialised diets became dangerous. Entire
• 2:12:40
  Speaker 1: ecosystems lost the productivity that had sustained them. Every known
• 2:12:45
  Speaker 1: non-avian dinosaur lineage eventually disappeared. So did pterosaurs, ammonites, and
• 2:12:50
  Speaker 1: many other groups. But not every dinosaur died. One branch survived.
• 2:12:57
  Speaker 1: The avian dinosaurs crossed the extinction boundary. They were small, adaptable,
• 2:13:02
  Speaker 1: and in some cases able to exploit foods and habitats
• 2:13:06
  Speaker 1: that remained available after the impact. From those surviving lineages
• 2:13:11
  Speaker 1: came the birds of the modern world. Today there are
• 2:13:14
  Speaker 1: more than 11,000 recognised living bird species. A sparrow, an eagle,
• 2:13:20
  Speaker 1: a penguin, a pigeon standing on a railway platform looking
• 2:13:24
  Speaker 1: mildly disappointed with everything. All of them belong to Dinosauria,
• 2:13:29
  Speaker 1: and that means the life and death of the dinosaurs
• 2:13:31
  Speaker 1: is not quite a story with a clean ending. Most
• 2:13:34
  Speaker 1: of the great evolutionary experiment vanished 66 million years ago.
• 2:13:39
  Speaker 1: The sauropods were gone, the horned dinosaurs were gone, the
• 2:13:43
  Speaker 1: armoured giants were gone, the great non-avian predators were gone.
• 2:13:48
  Speaker 1: But one small branch endured. So whenever a bird crosses
• 2:13:52
  Speaker 1: the sky, settles on a branch, builds a nest or
• 2:13:56
  Speaker 1: calls from somewhere outside the window, it is carrying forward
• 2:14:00
  Speaker 1: an evolutionary history that began more than 200 million years ago.
• 2:14:04
  Speaker 1: The age of the dinosaurs ended, and, in another sense...
• 2:14:09
  Speaker 1: It never did.