Transcript

5.29.25 · Smithsonian Magazine

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Speaker 1: Welcome. This is Rebecca Shore for Radio Eye and to
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day I will be reading the Smithsonian Magazine day to
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June twenty twenty five. As a reminder, Radio Eye is
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a reading service intended for people who are blind or
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have other disabilities that make it difficult to read printed material.
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Please join me now for the article titled A Trove
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of ice age fossils Buried in a Wyoming Cave is
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Rewriting Our Understanding of prehistoric Animals by Michael ray Taylor.
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Julie Meechen, an expert in ice age megafauna, skirts a
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dirt ledge called the Saddle deep inside a remarkable hollow
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in northern Wyoming known as Natural Trap Cave. She stops
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to observe Megan Hormel, a graduate student at Des Moines
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University and one of several volunteers who have repelled into
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the cave on a nylon line dangling from the entrance
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eighty feet overhead. Sunlight streams through a jagged skylight to
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illuminate a bell shaped chamber one hundred and forty feet
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in diameter. I sit to one side of the saddle
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as remains of ice age mammals slowly emerge into the
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light Like the scientists scattered over the subterranean hillside. I
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wear warm clothing, boots, and a caving helmet. My cumbersome
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climbing gear rests along with everyone else's on a tarp
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above ground on the western flank of the Big Horn Mountains,
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less than two miles from the Montana border. It is
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a scorching July day down here. The temperature hovers at
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a near constant forty two degrees fahrenheit, shifting only a
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few degrees with seasonal heat waves or blizzards. Bundled in
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thick coveralls in fleece jackets, the researchers wheeled trowels with
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gloved hands. It is the next to last day of
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a two week expedition. The twenty two members on this
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twenty twenty four dig include dude seasoned scientists and students
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undergraduate to postdoctoral, along with expert cave explorers who insure
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the safety and smooth operation of delicate work at the
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bottom of a deadly pit. The cave's name natural trap
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is literal. Over the past one hundred fifty thousand years,
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countless animals have fallen into it when approached from the
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relatively flat plain to the east, the pit appears suddenly
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beneath a small rise. You can see how tens of
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thousands of years ago, carnivores and the herbivores they chased
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could miss the black shadow until it was too late,
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perhaps because they were running or because of their relative
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weights and body shapes. Certain animals fell more horizontally, landing
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on the cave's floor well beyond the seventy five foot
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perimeter of the entrance and dying on impact. As the
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debris pile grew over millennia, some animals that fell rolled
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or bounced, creating the broad field of bones that fills
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the chamber to day, the bones of at least one Miracinux,
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an extinct cat commonly known as the American cheetah, stayed together.
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Its intact skeleton was observed on a ledge deep inside
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the cave in twenty twenty three. Each soil layer has
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a name related to its color and composition. Hormel works
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in the cobbly gray, lower than blocky brown and higher
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than rocky cheetah. Others work farther down slope, each focused
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on small fines. For example, Andrew Grass, a geoscientist digging
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thirty feet away, has compared the teeth of an extinct
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species of American horses from different periods within the pit,
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using them to build a temporal road map of changing
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tooth morphologies. He has just extracted a new equid molar
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to add to the mix. Setting aside her pick Hornmell
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cleans an exposed bone with a sort of small paint
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brush normally used on a interior trim. A foot or
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so to her right, a bony plate the size of
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an iPad angles upward from the dirt. A scapula from
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an animal closely related to present day big horn sheep,
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a male. If it matches the skull fragment that Tony Hotchner,
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another graduate student, found just yesterday, perhaps twenty three thousand
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years old, based on the dating of previous fines within
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the cobbly gray. This is another vert, Hormel tells Mitchen,
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using palaeontological shorthand for vertebra. Mitchen nods, after you get
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the vert out, I would take this little wall down.
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She indicates a jumble of packed rocks and dirt to
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the left of the scapula. Yeah, the wall has to go,
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but there's ribs in the wall. Hormel says, Okay, do
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your best to start taking it down, take that little
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nubbin out, and then worry about the scapula. Meechen says,
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that's a beautiful scapula, and I'd love to get it out.
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These workers are not hunting future museum displays. Instead, by
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documenting subtle changes within animal species over time, they seek
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clues to extreme climate changes of the past, and Natural
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Trap Cave provides an astoundingly well suited resource for the purpose,
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holding a largely unbroken record of mammal lineages going back
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tens of thousands of years. It's an amazing place, says
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Kirk Johnson, a palaeontologist and the director of the Smithsonian's
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National Museum of Natural History, who visited the cave himself
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twenty five years ago. It is a single site and
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the time range over which it was open is long,
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so it has the potential to show change over time
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as long as the individual skeletons are dated. That's why
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Meetchen and her team are focusing on the past thirty
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nine thousand years, a time starting in the late Pleistocene
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that coincides with the most carefully dated bone bearing layers
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inside the cave, deposits that were laid maaid down during
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a continuous cycle of glaciers advancing and retreating. We're going
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to see if we can accurately model the dry and
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wet cycles at the site during that period. Beechen says
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this sort of climate analysis based on slow changes in
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animal teeth as well as their mass and other attributes
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at a single site has never been published in the
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scientific literature. Grass's examination of horse teeth, for example, helps
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us better understand animals that have been regularly found in
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the pit, including two similar genera of Native American horses.
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Grass found that the enamel patterns on what is called
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the occlusal or biting surface of the tooth are different
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for each species. Researchers Lili and Spencer and Eric Scott
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also studied the ways horse teeth and those of bighorn
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sheep were worn down differently from different foods, and concluded
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that their diets were much like those of the wildebeests
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and zabras of the modern African serengetti. There, the wildebeests
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come through first and eat new, softer vegetation, while zebras
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come later, eating the tougher, older grass. The rate of
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toothware on horses and sheep over time can point toward
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wetter or drier climates, changes that can be confirmed by
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plant DNA preserved here animal remains. Another project by Thomas
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mc kinley, a geophysicist at the University of Wyoming, not
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only tracked shifting vegetation by extracting carbon isotopes and pollen
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from native plants, sagebrush, junipers, daisies, grasses, and members of
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the genus amaranthus from specific layers in the mound. It
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also created a new tool to date soil and fossils
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within a particular section, simultaneously showing whether the climate was
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wetter or drier when each layer was laid down. A
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combination of pollen counts and carbonate values suggests times of
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relatively wet summers within the heavy glaciation period starting as
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early as one hundred fifty thousand years ago. This generally
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forced the same plants to survive amid step like cold
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and dry conditions. A dozen of these and other groundbreaking
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studies were published in a special issue of the journal
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Coternary International in twenty twenty three, but in an essay
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introducing the issue, Meetchen and a colleague wrote that the
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volume was only the beginning, and that through many future
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studies and analyzes, Natural Trap Cave will continue to change
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our view of the Pleistocene world. Beyond dating and comparing findes,
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Meetchen and her colleagues are connecting the remains of individual
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species inside the cave to a long lasting migration pathway
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up on the surface, A pathway that is now clear
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helped shape the world population of mammals today. We know
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that we're seeing migration of different species tied to changing climates,
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she says, But can we better understand how these climates
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affected them? Do we see patterns? What kind of patterns
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might they indicate? From modern animals and a drying climate.
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Answering these questions requires a diverse set of tools that
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were not yet invented when the site was first researched
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in the nineteen sixties. Now, by casting a wide net
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across disciplines, Nietzschen and her colleagues are bringing assorted bits
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of evidence into sharp focus. Earth's past two point five
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billion years included five known glaciation periods, when global temperatures
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plummeted and vast ice sheets advanced across the planet, starting
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long before Natural Trap Cave began to form. The last
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glacial maximum ran from about nineteen thousand years ago to
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twenty nine thousand years ago. When the last glacial maximum began,
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an ice sheet covered most of the continent, reaching from
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the Arctic to present day Bathin Bay in the east
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and southern Montana in the west. A narrower ice sheet
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ran down the west coast. Sometimes this sheet expanded eastward
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to merge with the other, but in warmer times the
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glaciers parted, opening the ice free corridor at least fifteen
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miles wide and sometimes much wider at its American end.
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This verdant freeway for migrating mammals lasted thousands of years.
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At a stretch before the last glacial maximum, large animals
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traveled in both directions. Mammoths and mastodons came from Asia
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to North America. The first horses and camels, smaller versions
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of those living to day, left their native North America
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for Asia, Africa, and Europe. As the animals migrated between continents,
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they enter bred. We are finding through ancient DNA that
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many of the species at Natural Trap Cave are hybrids
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between North American and Eurasian populations. Meechin explains when a
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colder climate expanded the glaciers, closing the ice free corridor.
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Descendants were stuck on separate ends for about fifteen thousand
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years before it reopened, allowing cross migration to resume. Then
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the glaciers melted further, raising sea levels that flooded the
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Bearing Strait, blocking intercontinental migration once again. Both when the
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corridor was open and when it was closed, large animals
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moved by the thousands directly through the area around Natural Trap.
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Wyoming Cave explorers first repelled into Natural Trap Cave in
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the late nineteen sixties. In nineteen seventy one, Lawrence Loewendorff,
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an archaeologist who had heard that there were bones in
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the cave, collected a few mammal fossils and a red
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jasper knife at the base of the pit. Other than
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the knife and a wooden artifact found in a pack
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rat's nest, thought to be the shaft of an atlatteral
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dart throwing tool, no human artifacts or remains were ever
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found there. Shortly after this discovery, the Bureau of Land Management,
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which controls the site, built a metal grate across the
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pit entrance to protect animals and people from falling in
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as well as to prevent looting, A lockable gait at
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the Great's Center allowed permitted scientific access. Loewendorf, returning in
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nineteen seventy two with paleontologist Carol Joe Russian, excavated a
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ten by ten foot pit inside the cave, where there
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I found a surprising wealth of Pleistocene species. The paleontologist
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Larry Martin, who led multiple subsequent excavations in the seventies
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and early eighties, declared it would take at least fifty
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years to uncover the secrets of natural trap, but in
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nineteen eighty five, fearful that continued digging might harm the
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fossil trove, the Bureau of Land Management closed the cave
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until new paleontological methods and tools became available. It remained
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closed for three decades until Nietchen came to the site
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in twenty fourteen. As a child, I always loved mammals,
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Mitchen recalls, I was not a dinosaur kid at all.
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I liked the taxidermied animals and the mummies. Raised in
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Chicago until she was five years old, she visited the
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Field Museum with her parents often in high school in Florida,
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where her family had moved for her mother's job, she
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worked in a veterinarian's office. As an undergraduate at the
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University of Florida, she enrolled in a paleontology course that
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led to a job normally held by graduate students in
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the university's extensive paleontology collection. I got to open drawers
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and look at these cool bones from animals that had
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been dead for hundreds of thousands, millions of years, she says,
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I was transfixed. She went on to earn her pH
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d in Ecology an evolutionary biology at the University of California,
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Los Angeles. While there, she conducted research at the nearby
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Librea tarpits and became familiar with late Pleistocene fauna. When
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she joined Des Moines University as a professor of anatomy,
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she began looking for a project that could extend her
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knowledge and the worlds of her chosen period of study.
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By twenty fourteen, on breaking research into the geology of
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cave formation, based on findings at a site just ten
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miles south, had helped explain the origins of natural trap,
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which only underlined the site's uniqueness. The cave's first passages
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were carved by rain water some three hundred million years ago.
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More than two hundred million years later, the Big Horn
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Mountains emerged, lifting the landscape to its present elevation. Another
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round of creation, this time from rock dissolving microbial acids
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carried upward by rising spring water, expanded the ancient caves
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from below and made new ones with large chimneys climbing
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toward the surface. When the roof of the largest cavity collapsed,
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it exposed a pit in the middle of a migratory pathway,
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essentially creating this perfectly placed and protected vault of intercontinental paleontology. Still,
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the cave presented unusual research challenges, as Pleistocene animals fell
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in periodic flooding washed away some remains, creating occasional gaps
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in the fossil record of the large excavation sound the
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sediment to position gets really complex. David M. Lovelace, a
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geoscientist at the University of Wisconsin Madison who led a
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comprehensive study of the cave's stratigraphy, explains sediment that's washing
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in an inn can leave little pockets of deposition in
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one area. Then the inlet or the stream will shifted
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slightly so it deposits in another area. Sometimes a fresh
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stream cuts through older sediment to drop in new surface material.
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It literally forms almost a new cave through the old sediment,
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so you can deposit younger material under older, previously existing material.
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The complexities become outstanding. The team's remarkable success at precise
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dating and turn allows Michen and other researchers to prioritize
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fossils within the best dated deposits, and in this way
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tracks slower evolutionary changes, the kind found between layers where
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thousands of years of evidence may have washed downhill. Since
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twenty fourteen, each team member has been taught vertical rope
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technique by Juan Leyden, a New Zealand climbing whiz who
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moved to Lander, Wyoming in the nineteen seventies. In addition
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to caving around the world, Leyden works as an arborist,
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leads mountain search and rescue sails extensively, and is an
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accomplished photographer. I have repelled into deep cave systems for
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more than forty years, but like everyone else allowed into
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natural trap, I first have to prove to Leyden that
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I can climb one hundred feet up a nylon rope
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about as thick as a finger. I take my mind.
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I exam up on the surface near the cave's entrance,
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where Leyden has installed a crane like metal contraption of
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his own design on the back of an old pick
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up truck with a pulley that allows him to gradually
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lower any length of rope while the climber remains a
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few feet off the ground. As I make my way
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to the truck, my metal ascenders clanking against one another.
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Leyden notes my dated gear. Most modern cavers use the
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European frog ascent system, but I cling to an arrangement
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called a rope walker, designed in the nineteen sixties for
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deep pits in Alabama and Mexico. I huff and puff
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fifty feet up the line until Leyden is finally satisfied
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that's enough, he says, at last, lowering me to the
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dusty ground. When it's time to enter the cave, another
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team member, Doug Warner, inspects my descending gear, an equally
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dated repel rack, a U shaped piece of metal loaded
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with break bars to control my rate of descent. Then
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I stand at the edge of the metal grate, trying
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not to stare at the darkness below. Warner surprises me
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with a whistle. Even more surprising, the whistle is answered
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by another from a few feet inside the cave. He
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points out, as says, Phoebe, a smallish gray bird with
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a brilliant yellow belly. She flutters about her nest in
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a precarious niche above the pit, trying to nudge her
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fledglings into flight, occasionally popping up through the grate to
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whistle at Warner. We've been talking for several days now,
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he says, checking that my carabiners are locked, then he
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pronounces me safe to descend. Scientists entering the cave clip
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into a safety line before walking across the grating to
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the metal door built in nineteen seventy one. A regular
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extension ladder oakes up through the opening, Still clipped into
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the safety, I climb ten feet down to a flat ledge,
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noting the excited bird and her peeping chicks. I walk
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to the edge, where the main descent line dangles free.
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I attach my rack to the main line, unclip from
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the safety, and step backward into space. Descending. I note
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another ledge, this one holding enormous nests of sticks built
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by raptors before the gate was installed. Then the walls
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recede below me, A shaft of sunlight illuminates a bright
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circle of the floor. Researchers move about like so many
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ants on an anhill. A caver at the bottom helps
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pull me over to unclip outside of the excavation zone,
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and I remove my climbing gear when I join the
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researchers underground, Hormel is extracting big horn bits while others
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dig elsewhere about the room. As the day progresses, the
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circle of light creeps across the floor. When it hits
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a certain boulder, I'm told it's lunch time. B. D. Voss,
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a geology education doctoral student, hands Meechen a small bone,
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seeking her opinion. She agrees that it's modern, not a fossil,
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maybe a packrat. Voss drops the bone into a plastic
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five gallon bucket. Seeing that it is nearly full. Voss
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carries the bucket to a designated dump pile, a growing
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mound that holds fifty years worth of excavation discards. Voss
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then returns to help Pormel pries out a few more
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vertebrae and ribs as they work their way toward the
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big horn. Scapula, which they finally pulled from the cobbly gray.
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Months later, lab work will reveal that what had appeared
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in the cave to be a nearly complete skeleton was
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actually parts from several sheep. A day's end, team members emerge,
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most carry packs with carefully labeled specimen bags. When it's
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my turn, I rope walk up about twenty five feet
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before stopping to catch my breath. Hanging in the air,
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I see beyond the mound, to the darkness of the
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larger cave, reaching into the distance. The scope of all
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I see from my elevated view separate layers of excavation
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blocked off with orange flags still untouched zones on the mound.
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The enticing entrance to the forbidden lower chamber suggests that
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many decades of research remain at Natural Trap Cave. I
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honestly think the work is endless, Mitchen says later, it
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certainly will outlast my career. I see no end to
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the questions we can ask about this sight. I emerge
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to a freshening breeze. Support cavers who remain near the
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entrance are gathered beneath a large blue tar, which now
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flutters in the afternoon winds, I join exiting team members
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under the tarp as they pull sports drinks from a cooler,
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discussing the day's work. Across Big Horn Canyon, I see
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the twin peaks of the prior mountains, home to about
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one hundred and twenty three roaming mustangs, European descendants of
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the extinct Eo Hippis. One horse from either the Jenis
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Equis or Harrington Hippis, both now extinct, contributed a tooth
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to today's findings. Only careful lab work will identify the
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horse's correct genus, species, and age. As the sun dips farther,
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we head toward camp, ambling through fragrant junipers on our
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way to the cook tent its roast and potatoes tonight,
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shouts John Logsdon, the project's longtime operations manager and chief cook,
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and since twenty twenty three, Nietchen's spouse. Everybody can have
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a potato. We have too many, so eat up. Hormel.
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An experienced cook assists in serving. We eat on paper plates.
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Camp chairs crowded beneath shade that moves with the setting sun.
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A short walk away, the empty tents of the team's
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camp rattle in the hot wind I get to take
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a shower in four days, Logsden says, wistfully doling out potatoes,
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that's about five days too late retorts a caver in
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the food line beyond the sheep and horse. The day's
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finds include part of a wolverine and an American cheetah.
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Petrosal bone, a marble like bone of the inner ear
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essential to balance. The patrosal is the hardest bone in
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all vertebrates, save for tooth enamel. Its hardness makes it
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ideal for preserving ancient DNA, so team members always celebrate
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a new patrosal the next morning. On the year's final
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day of digging, they will cheer once more as Hotchner
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discovers a mammoth vertebra. Each preserved tooth vertebra and neural
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fiber presents a thread in Natural Trap Cave's evolutionary tapestry,
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helping to identify species and provide evidence of incremental changes
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in bone density, food sources, or habitat. Nietzschen says her
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next project will look at aridity through time at Natural
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Trap Cave. Funding could be tricky. She now worries that
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support from the National Science Foundation a crucial source may
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vanish entirely. My fingers and toes are crossed. But if
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she could proceed, she says, we'll be able to determine
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how large and eventually small ant mammals respond to relatively
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rapid drying events, and clues to how some species survive
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climatic changes in the prehistoric past could prove vital as
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the planet grows rapidly warmer and drier. One thing I've
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learned about late plis to see megafauna is that they
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were pretty resilient. Mitchen says, right until some yet to
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be discovered climate threshold was crossed, causing nast death. It
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took a lot of things simultaneously to kill them off,
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but once that cascade happened, it couldn't be stopped. I
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guess that's the scariest part for fauna to day. They've
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been through a lot, but once you hit the perfect
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balance of low population sizes and habitat loss, it's too late.
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I hope that lesson isn't lost on us. Finally, ask Smithsonian,
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you've got questions, we've got experts. What are the factors
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that limit the altitude a house fly can reach? That's
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from Monica Cartwright, North Wales, Pennsylvania. The answer is from
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Floyd Shockley, Curator of Entomology, National Museum of Natural History.
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The maximum height to which any insect can fly is
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based on three factors that change with altitude. One is temperature.
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At a certain point, an insect flies high enough that
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the air is too cold and it comes back down.
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The second is air density. When the air gets too
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thin at greater heights, the insect's wings can't propel it
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as well in the air. The third is oxygen, which
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insects need and which becomes less plentiful higher up. That said,
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plenty of insects can be found at high altitudes. Insects
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that live in mountainous areas have evolved ways to compensate
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for these environmental conditions. Flies have been collected at altitudes
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higher than twenty thousand feet above sea level. Some migratory
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species of butterfly purposefully take advantage of the lower energy
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cost of flying at high altitudes because it is easier
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for them to ride wind currents there. This concludes readings
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from the Smithsonian Magazine for to day. Your reader has
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been Rebecca Shore. Thank you for listening, and have a
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great day.