5.29.25

Episode Transcript

Speaker 1 (00:01):
Welcome. This is Rebecca Shore for Radio Eye and to
day I will be reading the Smithsonian Magazine day to
June twenty twenty five. As a reminder, Radio Eye is
a reading service intended for people who are blind or
have other disabilities that make it difficult to read printed material.
Please join me now for the article titled A Trove

(00:23):
of ice age fossils Buried in a Wyoming Cave is
Rewriting Our Understanding of prehistoric Animals by Michael ray Taylor.
Julie Meechen, an expert in ice age megafauna, skirts a
dirt ledge called the Saddle deep inside a remarkable hollow

(00:43):
in northern Wyoming known as Natural Trap Cave. She stops
to observe Megan Hormel, a graduate student at Des Moines
University and one of several volunteers who have repelled into
the cave on a nylon line dangling from the entrance
eighty feet overhead. Sunlight streams through a jagged skylight to

(01:04):
illuminate a bell shaped chamber one hundred and forty feet
in diameter. I sit to one side of the saddle
as remains of ice age mammals slowly emerge into the
light Like the scientists scattered over the subterranean hillside. I
wear warm clothing, boots, and a caving helmet. My cumbersome
climbing gear rests along with everyone else's on a tarp

(01:28):
above ground on the western flank of the Big Horn Mountains,
less than two miles from the Montana border. It is
a scorching July day down here. The temperature hovers at
a near constant forty two degrees fahrenheit, shifting only a
few degrees with seasonal heat waves or blizzards. Bundled in
thick coveralls in fleece jackets, the researchers wheeled trowels with

(01:51):
gloved hands. It is the next to last day of
a two week expedition. The twenty two members on this
twenty twenty four dig include dude seasoned scientists and students
undergraduate to postdoctoral, along with expert cave explorers who insure
the safety and smooth operation of delicate work at the
bottom of a deadly pit. The cave's name natural trap

(02:14):
is literal. Over the past one hundred fifty thousand years,
countless animals have fallen into it when approached from the
relatively flat plain to the east, the pit appears suddenly
beneath a small rise. You can see how tens of
thousands of years ago, carnivores and the herbivores they chased
could miss the black shadow until it was too late,

(02:37):
perhaps because they were running or because of their relative
weights and body shapes. Certain animals fell more horizontally, landing
on the cave's floor well beyond the seventy five foot
perimeter of the entrance and dying on impact. As the
debris pile grew over millennia, some animals that fell rolled
or bounced, creating the broad field of bones that fills

(03:00):
the chamber to day, the bones of at least one Miracinux,
an extinct cat commonly known as the American cheetah, stayed together.
Its intact skeleton was observed on a ledge deep inside
the cave in twenty twenty three. Each soil layer has
a name related to its color and composition. Hormel works

(03:22):
in the cobbly gray, lower than blocky brown and higher
than rocky cheetah. Others work farther down slope, each focused
on small fines. For example, Andrew Grass, a geoscientist digging
thirty feet away, has compared the teeth of an extinct
species of American horses from different periods within the pit,

(03:43):
using them to build a temporal road map of changing
tooth morphologies. He has just extracted a new equid molar
to add to the mix. Setting aside her pick Hornmell
cleans an exposed bone with a sort of small paint
brush normally used on a interior trim. A foot or
so to her right, a bony plate the size of

(04:04):
an iPad angles upward from the dirt. A scapula from
an animal closely related to present day big horn sheep,
a male. If it matches the skull fragment that Tony Hotchner,
another graduate student, found just yesterday, perhaps twenty three thousand
years old, based on the dating of previous fines within
the cobbly gray. This is another vert, Hormel tells Mitchen,

(04:29):
using palaeontological shorthand for vertebra. Mitchen nods, after you get
the vert out, I would take this little wall down.
She indicates a jumble of packed rocks and dirt to
the left of the scapula. Yeah, the wall has to go,
but there's ribs in the wall. Hormel says, Okay, do
your best to start taking it down, take that little

(04:51):
nubbin out, and then worry about the scapula. Meechen says,
that's a beautiful scapula, and I'd love to get it out.
These workers are not hunting future museum displays. Instead, by
documenting subtle changes within animal species over time, they seek
clues to extreme climate changes of the past, and Natural

(05:11):
Trap Cave provides an astoundingly well suited resource for the purpose,
holding a largely unbroken record of mammal lineages going back
tens of thousands of years. It's an amazing place, says
Kirk Johnson, a palaeontologist and the director of the Smithsonian's
National Museum of Natural History, who visited the cave himself

(05:32):
twenty five years ago. It is a single site and
the time range over which it was open is long,
so it has the potential to show change over time
as long as the individual skeletons are dated. That's why
Meetchen and her team are focusing on the past thirty
nine thousand years, a time starting in the late Pleistocene

(05:53):
that coincides with the most carefully dated bone bearing layers
inside the cave, deposits that were laid maaid down during
a continuous cycle of glaciers advancing and retreating. We're going
to see if we can accurately model the dry and
wet cycles at the site during that period. Beechen says
this sort of climate analysis based on slow changes in

(06:16):
animal teeth as well as their mass and other attributes
at a single site has never been published in the
scientific literature. Grass's examination of horse teeth, for example, helps
us better understand animals that have been regularly found in
the pit, including two similar genera of Native American horses.

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Grass found that the enamel patterns on what is called
the occlusal or biting surface of the tooth are different
for each species. Researchers Lili and Spencer and Eric Scott
also studied the ways horse teeth and those of bighorn
sheep were worn down differently from different foods, and concluded
that their diets were much like those of the wildebeests

(06:59):
and zabras of the modern African serengetti. There, the wildebeests
come through first and eat new, softer vegetation, while zebras
come later, eating the tougher, older grass. The rate of
toothware on horses and sheep over time can point toward
wetter or drier climates, changes that can be confirmed by

(07:20):
plant DNA preserved here animal remains. Another project by Thomas
mc kinley, a geophysicist at the University of Wyoming, not
only tracked shifting vegetation by extracting carbon isotopes and pollen
from native plants, sagebrush, junipers, daisies, grasses, and members of

(07:40):
the genus amaranthus from specific layers in the mound. It
also created a new tool to date soil and fossils
within a particular section, simultaneously showing whether the climate was
wetter or drier when each layer was laid down. A
combination of pollen counts and carbonate values suggests times of

(08:02):
relatively wet summers within the heavy glaciation period starting as
early as one hundred fifty thousand years ago. This generally
forced the same plants to survive amid step like cold
and dry conditions. A dozen of these and other groundbreaking
studies were published in a special issue of the journal

(08:24):
Coternary International in twenty twenty three, but in an essay
introducing the issue, Meetchen and a colleague wrote that the
volume was only the beginning, and that through many future
studies and analyzes, Natural Trap Cave will continue to change
our view of the Pleistocene world. Beyond dating and comparing findes,

(08:48):
Meetchen and her colleagues are connecting the remains of individual
species inside the cave to a long lasting migration pathway
up on the surface, A pathway that is now clear
helped shape the world population of mammals today. We know
that we're seeing migration of different species tied to changing climates,

(09:09):
she says, But can we better understand how these climates
affected them? Do we see patterns? What kind of patterns
might they indicate? From modern animals and a drying climate.
Answering these questions requires a diverse set of tools that
were not yet invented when the site was first researched

(09:29):
in the nineteen sixties. Now, by casting a wide net
across disciplines, Nietzschen and her colleagues are bringing assorted bits
of evidence into sharp focus. Earth's past two point five
billion years included five known glaciation periods, when global temperatures
plummeted and vast ice sheets advanced across the planet, starting

(09:54):
long before Natural Trap Cave began to form. The last
glacial maximum ran from about nineteen thousand years ago to
twenty nine thousand years ago. When the last glacial maximum began,
an ice sheet covered most of the continent, reaching from
the Arctic to present day Bathin Bay in the east

(10:15):
and southern Montana in the west. A narrower ice sheet
ran down the west coast. Sometimes this sheet expanded eastward
to merge with the other, but in warmer times the
glaciers parted, opening the ice free corridor at least fifteen
miles wide and sometimes much wider at its American end.

(10:38):
This verdant freeway for migrating mammals lasted thousands of years.
At a stretch before the last glacial maximum, large animals
traveled in both directions. Mammoths and mastodons came from Asia
to North America. The first horses and camels, smaller versions
of those living to day, left their native North America

(11:01):
for Asia, Africa, and Europe. As the animals migrated between continents,
they enter bred. We are finding through ancient DNA that
many of the species at Natural Trap Cave are hybrids
between North American and Eurasian populations. Meechin explains when a
colder climate expanded the glaciers, closing the ice free corridor.

(11:26):
Descendants were stuck on separate ends for about fifteen thousand
years before it reopened, allowing cross migration to resume. Then
the glaciers melted further, raising sea levels that flooded the
Bearing Strait, blocking intercontinental migration once again. Both when the

(11:46):
corridor was open and when it was closed, large animals
moved by the thousands directly through the area around Natural Trap.
Wyoming Cave explorers first repelled into Natural Trap Cave in
the late nineteen sixties. In nineteen seventy one, Lawrence Loewendorff,

(12:07):
an archaeologist who had heard that there were bones in
the cave, collected a few mammal fossils and a red
jasper knife at the base of the pit. Other than
the knife and a wooden artifact found in a pack
rat's nest, thought to be the shaft of an atlatteral
dart throwing tool, no human artifacts or remains were ever

(12:28):
found there. Shortly after this discovery, the Bureau of Land Management,
which controls the site, built a metal grate across the
pit entrance to protect animals and people from falling in
as well as to prevent looting, A lockable gait at
the Great's Center allowed permitted scientific access. Loewendorf, returning in

(12:51):
nineteen seventy two with paleontologist Carol Joe Russian, excavated a
ten by ten foot pit inside the cave, where there
I found a surprising wealth of Pleistocene species. The paleontologist
Larry Martin, who led multiple subsequent excavations in the seventies
and early eighties, declared it would take at least fifty

(13:14):
years to uncover the secrets of natural trap, but in
nineteen eighty five, fearful that continued digging might harm the
fossil trove, the Bureau of Land Management closed the cave
until new paleontological methods and tools became available. It remained
closed for three decades until Nietchen came to the site

(13:35):
in twenty fourteen. As a child, I always loved mammals,
Mitchen recalls, I was not a dinosaur kid at all.
I liked the taxidermied animals and the mummies. Raised in
Chicago until she was five years old, she visited the
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
worked in a veterinarian's office. As an undergraduate at the
University of Florida, she enrolled in a paleontology course that
led to a job normally held by graduate students in
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
been dead for hundreds of thousands, millions of years, she says,
I was transfixed. She went on to earn her pH
d in Ecology an evolutionary biology at the University of California,
Los Angeles. While there, she conducted research at the nearby

(14:40):
Librea tarpits and became familiar with late Pleistocene fauna. When
she joined Des Moines University as a professor of anatomy,
she began looking for a project that could extend her
knowledge and the worlds of her chosen period of study.
By twenty fourteen, on breaking research into the geology of

(15:02):
cave formation, based on findings at a site just ten
miles south, had helped explain the origins of natural trap,
which only underlined the site's uniqueness. The cave's first passages
were carved by rain water some three hundred million years ago.
More than two hundred million years later, the Big Horn

(15:22):
Mountains emerged, lifting the landscape to its present elevation. Another
round of creation, this time from rock dissolving microbial acids
carried upward by rising spring water, expanded the ancient caves
from below and made new ones with large chimneys climbing
toward the surface. When the roof of the largest cavity collapsed,

(15:46):
it exposed a pit in the middle of a migratory pathway,
essentially creating this perfectly placed and protected vault of intercontinental paleontology. Still,
the cave presented unusual research challenges, as Pleistocene animals fell
in periodic flooding washed away some remains, creating occasional gaps

(16:09):
in the fossil record of the large excavation sound the
sediment to position gets really complex. David M. Lovelace, a
geoscientist at the University of Wisconsin Madison who led a
comprehensive study of the cave's stratigraphy, explains sediment that's washing
in an inn can leave little pockets of deposition in

(16:31):
one area. Then the inlet or the stream will shifted
slightly so it deposits in another area. Sometimes a fresh
stream cuts through older sediment to drop in new surface material.
It literally forms almost a new cave through the old sediment,
so you can deposit younger material under older, previously existing material.

(16:54):
The complexities become outstanding. The team's remarkable success at precise
dating and turn allows Michen and other researchers to prioritize
fossils within the best dated deposits, and in this way
tracks slower evolutionary changes, the kind found between layers where

(17:15):
thousands of years of evidence may have washed downhill. Since
twenty fourteen, each team member has been taught vertical rope
technique by Juan Leyden, a New Zealand climbing whiz who
moved to Lander, Wyoming in the nineteen seventies. In addition
to caving around the world, Leyden works as an arborist,

(17:36):
leads mountain search and rescue sails extensively, and is an
accomplished photographer. I have repelled into deep cave systems for
more than forty years, but like everyone else allowed into
natural trap, I first have to prove to Leyden that
I can climb one hundred feet up a nylon rope
about as thick as a finger. I take my mind.

(18:00):
I exam up on the surface near the cave's entrance,
where Leyden has installed a crane like metal contraption of
his own design on the back of an old pick
up truck with a pulley that allows him to gradually
lower any length of rope while the climber remains a
few feet off the ground. As I make my way

(18:20):
to the truck, my metal ascenders clanking against one another.
Leyden notes my dated gear. Most modern cavers use the
European frog ascent system, but I cling to an arrangement
called a rope walker, designed in the nineteen sixties for
deep pits in Alabama and Mexico. I huff and puff

(18:41):
fifty feet up the line until Leyden is finally satisfied
that's enough, he says, at last, lowering me to the
dusty ground. When it's time to enter the cave, another
team member, Doug Warner, inspects my descending gear, an equally
dated repel rack, a U shaped piece of metal loaded

(19:01):
with break bars to control my rate of descent. Then
I stand at the edge of the metal grate, trying
not to stare at the darkness below. Warner surprises me
with a whistle. Even more surprising, the whistle is answered
by another from a few feet inside the cave. He
points out, as says, Phoebe, a smallish gray bird with

(19:25):
a brilliant yellow belly. She flutters about her nest in
a precarious niche above the pit, trying to nudge her
fledglings into flight, occasionally popping up through the grate to
whistle at Warner. We've been talking for several days now,
he says, checking that my carabiners are locked, then he
pronounces me safe to descend. Scientists entering the cave clip

(19:50):
into a safety line before walking across the grating to
the metal door built in nineteen seventy one. A regular
extension ladder oakes up through the opening, Still clipped into
the safety, I climb ten feet down to a flat ledge,
noting the excited bird and her peeping chicks. I walk
to the edge, where the main descent line dangles free.

(20:14):
I attach my rack to the main line, unclip from
the safety, and step backward into space. Descending. I note
another ledge, this one holding enormous nests of sticks built
by raptors before the gate was installed. Then the walls
recede below me, A shaft of sunlight illuminates a bright

(20:37):
circle of the floor. Researchers move about like so many
ants on an anhill. A caver at the bottom helps
pull me over to unclip outside of the excavation zone,
and I remove my climbing gear when I join the
researchers underground, Hormel is extracting big horn bits while others

(20:57):
dig elsewhere about the room. As the day progresses, the
circle of light creeps across the floor. When it hits
a certain boulder, I'm told it's lunch time. B. D. Voss,
a geology education doctoral student, hands Meechen a small bone,
seeking her opinion. She agrees that it's modern, not a fossil,

(21:20):
maybe a packrat. Voss drops the bone into a plastic
five gallon bucket. Seeing that it is nearly full. Voss
carries the bucket to a designated dump pile, a growing
mound that holds fifty years worth of excavation discards. Voss
then returns to help Pormel pries out a few more

(21:41):
vertebrae and ribs as they work their way toward the
big horn. Scapula, which they finally pulled from the cobbly gray.
Months later, lab work will reveal that what had appeared
in the cave to be a nearly complete skeleton was
actually parts from several sheep. A day's end, team members emerge,

(22:03):
most carry packs with carefully labeled specimen bags. When it's
my turn, I rope walk up about twenty five feet
before stopping to catch my breath. Hanging in the air,
I see beyond the mound, to the darkness of the
larger cave, reaching into the distance. The scope of all
I see from my elevated view separate layers of excavation

(22:26):
blocked off with orange flags still untouched zones on the mound.
The enticing entrance to the forbidden lower chamber suggests that
many decades of research remain at Natural Trap Cave. I
honestly think the work is endless, Mitchen says later, it
certainly will outlast my career. I see no end to

(22:48):
the questions we can ask about this sight. I emerge
to a freshening breeze. Support cavers who remain near the
entrance are gathered beneath a large blue tar, which now
flutters in the afternoon winds, I join exiting team members
under the tarp as they pull sports drinks from a cooler,

(23:09):
discussing the day's work. Across Big Horn Canyon, I see
the twin peaks of the prior mountains, home to about
one hundred and twenty three roaming mustangs, European descendants of
the extinct Eo Hippis. One horse from either the Jenis
Equis or Harrington Hippis, both now extinct, contributed a tooth

(23:30):
to today's findings. Only careful lab work will identify the
horse's correct genus, species, and age. As the sun dips farther,
we head toward camp, ambling through fragrant junipers on our
way to the cook tent its roast and potatoes tonight,
shouts John Logsdon, the project's longtime operations manager and chief cook,

(23:53):
and since twenty twenty three, Nietchen's spouse. Everybody can have
a potato. We have too many, so eat up. Hormel.
An experienced cook assists in serving. We eat on paper plates.
Camp chairs crowded beneath shade that moves with the setting sun.
A short walk away, the empty tents of the team's

(24:15):
camp rattle in the hot wind I get to take
a shower in four days, Logsden says, wistfully doling out potatoes,
that's about five days too late retorts a caver in
the food line beyond the sheep and horse. The day's
finds include part of a wolverine and an American cheetah.

(24:36):
Petrosal bone, a marble like bone of the inner ear
essential to balance. The patrosal is the hardest bone in
all vertebrates, save for tooth enamel. Its hardness makes it
ideal for preserving ancient DNA, so team members always celebrate
a new patrosal the next morning. On the year's final

(24:58):
day of digging, they will cheer once more as Hotchner
discovers a mammoth vertebra. Each preserved tooth vertebra and neural
fiber presents a thread in Natural Trap Cave's evolutionary tapestry,
helping to identify species and provide evidence of incremental changes

(25:18):
in bone density, food sources, or habitat. Nietzschen says her
next project will look at aridity through time at Natural
Trap Cave. Funding could be tricky. She now worries that
support from the National Science Foundation a crucial source may
vanish entirely. My fingers and toes are crossed. But if

(25:42):
she could proceed, she says, we'll be able to determine
how large and eventually small ant mammals respond to relatively
rapid drying events, and clues to how some species survive
climatic changes in the prehistoric past could prove vital as
the planet grows rapidly warmer and drier. One thing I've

(26:06):
learned about late plis to see megafauna is that they
were pretty resilient. Mitchen says, right until some yet to
be discovered climate threshold was crossed, causing nast death. It
took a lot of things simultaneously to kill them off,
but once that cascade happened, it couldn't be stopped. I
guess that's the scariest part for fauna to day. They've

(26:29):
been through a lot, but once you hit the perfect
balance of low population sizes and habitat loss, it's too late.
I hope that lesson isn't lost on us. Finally, ask Smithsonian,
you've got questions, we've got experts. What are the factors
that limit the altitude a house fly can reach? That's

(26:51):
from Monica Cartwright, North Wales, Pennsylvania. The answer is from
Floyd Shockley, Curator of Entomology, National Museum of Natural History.
The maximum height to which any insect can fly is
based on three factors that change with altitude. One is temperature.
At a certain point, an insect flies high enough that

(27:13):
the air is too cold and it comes back down.
The second is air density. When the air gets too
thin at greater heights, the insect's wings can't propel it
as well in the air. The third is oxygen, which
insects need and which becomes less plentiful higher up. That said,
plenty of insects can be found at high altitudes. Insects

(27:35):
that live in mountainous areas have evolved ways to compensate
for these environmental conditions. Flies have been collected at altitudes
higher than twenty thousand feet above sea level. Some migratory
species of butterfly purposefully take advantage of the lower energy
cost of flying at high altitudes because it is easier

(27:57):
for them to ride wind currents there. This concludes readings
from the Smithsonian Magazine for to day. Your reader has
been Rebecca Shore. Thank you for listening, and have a
great day.