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It’s a trap! Natural Trap Cave spurs scientific study of the ancient world

Justin Sipla ascends up a rope 80 feet after working at the bottom of the Natural Trap Cave in north-central Wyoming in July. Scientists have resumed digging for the first time in more than 30 years. Justin Sipla ascends up a rope 80 feet after working at the bottom of the Natural Trap Cave in north-central Wyoming in July. Scientists have resumed digging for the first time in more than 30 years. Bureau of Land Management photo

Try picturing the Big Horn Mountains 100,000 years ago. Same topography; plant life would have differed, though not significantly from the flora found there today.

Much of the wildlife would be completely different, since many species vanished millenniums ago.

Now, imagine a scientific treasure trove of stone providing verification of the wide variety of creatures roaming the Big Horn Basin long ago ...

A few fossils were found in the Natural Trap Cave more than 40 years ago in the Big Horn Mountains, with thousands of animal remains dating back thousands of years. Now scientists have returned, armed with new technology to better understand fauna of the distant past.

“It’s been a big find since the ’70s,” said geologist Gretchen Hurley of the Cody Bureau of Land Management. Hurley was the project leader for a 10-day excavation that took place this summer and will resume the next two summers.

Natural Trap is an apt name for the cave. It’s a hole with no escape, even if the victim survived the fall. Its blind approach is a slight rise of crumbling limestone. The cavern is 15 feet wide by 85 feet deep, with walls so steep no animal could possibly escape.

A locked steel grate covers the pit, which now is a mausoleum containing remains of many animals that haven’t walked the earth for thousands of years.

“Natural Trap Cave was the first major Pleistocene locality to be developed in northern Wyoming, and the recovery of more than 30,000 specimens representing a wide variety of vertebrates has established it as one of the major late Pleistocene sites in North American,” stated a 1978 paper by B. Miles Gilbert and Larry D. Martin.

“A lot of bones,” Hurley said concisely.

No human remains have been unearthed. It is most likely locals were well aware of the cave.

“That being said, it is possible that human remains could still be found in cave sediment as a result of future excavations,” Hurley added.

Bits of arrow points and part of an atlatl shaft have been unearthed, Hurley said. An atlatl is a device that greatly increases a spear’s velocity.

One complete skeleton unearthed is the North American cheetah, Hurley said.

Scientists theorized that pronghorns may have developed their speed to outrun the swift, long-limbed Pleistocene cheetah.

Western camels, bison and several varieties of horses were inhabitants, according to a 1978 paper by Larry Martin and Gilbert.

There’s the stilt-legged horse, “probably smaller than a miniature horse,” Hurley said.

They also found many many species of microfauna not collected in previous years, said Julie Meachen, Des Moines University assistant professor of anatomy.

“The types of microfauna we have found so far include multiple species of rodents, lizards, snakes, birds, frogs and even fish,” Meachen said. “Some of these deposits may be Holocene (10,000 years to present) in age, but some are also probably Pleistocene (1,640,000 to about 10,000 years ago).

“So far, we think they are deposits from raptors or owls. I have a team member looking into this data, and there is a student working on the lizard fauna right now.”

Other extinct mammals found in the Pleistocene levels in the cave include a pine martin, short-faced bear, dire wolf, American lion, American cheetah, mammoth, American camel, woodland musk ox, ancient bison and bighorn sheep, according to Gilbert and Martin.

Short-faced bears were about 25 percent bulkier than present-day grizzly bears and sported longer front legs and a stump nose, Hurley said.

Pleistocene short-faced bears weighed up to 2,500 pounds. The largest modern-day bear found was a 2,200-pound polar bear, according to National Geographic. A sketch depicts the short-nose on its hind legs standing easily twice the height of a human.

The last continental glacier petered out about 10,000 years ago, but there were no glaciers in the vicinity of the cave. There was more precipitation and more conifers, Hurley said.

Plant cover may have been similar to what is found in the Big Horn’s high mountain meadows, according to a 1978 paper by Martin and Gilbert.

The cave is like a damp refrigerator, preserving immaculate specimens, according to the scientists.

The present summertime temperature in the cave is 41 degrees Fahrenheit, a 1993 paper by Xiaoming Wang and Martin reported.

“Humidity is much higher inside the cave than outside, due to moisture being trapped in the ambient air, as well as entering the cave from water contained in moist limestone that makes up the cave,” Hurley said. “Temperatures inside are cooler as well, which allows for excellent preservation of fossil (Holocene and Pleistocene) DNA in bone and other organic material,” Hurley said.

“My collaborator Alan Cooper is currently analyzing the ancient DNA of these species in his lab at the Australia Center for Ancient DNA at the University of Adelaide and will hopefully have some results by the end of the year,” Meachen said.

Sediment covers the bones in layers.

“The fact that it is a stratified (sedimentary rock) deposit composed of dated levels enhances the usefulness of this locality in tracing the environmental and evolutionary changes in this community  during the late Pleistocene and early Holocene and permits us to examine in detail some of the parameters assumed by the climatic model of extinction,” Gilbert and Martin wrote in 1984.

Today, grass, brush and juniper dot the beautiful landscape around the hole. The Pleistocene epoch is ephemeral in Earth time, considering this planet has existed some 4.5 billion years. Sitting at the pit’s rim picturing massive bison, mammoth or predators like huge bears and lions stalking the foothills certainly triggers the imagination.

The exact location is not widely known, although it is marked with a sign.

“The potential information coming out of this hole is something we can’t fathom yet,” Hurley said.

American cheetahs once roamed the Big Horn Mountains and at least one didn’t make the jump across the 15-foot chasm of the Natural Trap Cave in the Big Horn Mountains.
Drawing courtesy Xiaoming Wang


  • posted by Kara

    December 02, 2014 4:07 pm

    How have I never heard of this before?

    Dang, Thanks Gib!

  • posted by Dewey

    December 02, 2014 12:00 pm

    Pleistocene Park.
    Call the cloners...the DNA is still good to go.

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