Natural Trap Cave: prehistoric lions, dire wolves, and bears, oh my!

Renewed excavation of Wyoming's Natural Trap Cave promises to be a boon for scientists, armed with a capability for ancient DNA sequencing not available in 1984, the last time the cave was open to exploration.

Bureau of Land Management/AP
Bureau of Land Management cave specialist Bryan McKenzie rappels into Natural Trap Cave in north-central Wyoming during a cleanup expedition. The cave holds the remains of tens of thousands of animals, including many now-extinct species, from the late Pleistocene period tens of thousands of years ago. This summer, scientists plan to venture back into the cave and resume digging for the first time in three decades.

Tens of thousands of years ago, woolly mammoths, American lions, and dire wolves stalked the foothills of Wyoming’s Big Horn Mountains. This summer, an international crew of paleontologists will get the chance to come face to face with what's left of these beasts of yore, buried deep in a prehistoric sinkhole.

For the first time in more than 30 years, the US Bureau of Land Management will open for excavation a subterranean cave believed to have formed eons ago. Des Moines University paleontologist Julie Meachen and a team of researchers from around the United States and Australia plan to descend 85-feet into the cave to excavate the fossilized remains of prehistoric giants of the Pleistocene Epoch.

Natural Trap Cave is 30 miles from the nearest town, Lovell, Wyo., and is accessible only by unpaved and rocky roads. It can take up to an hour and a half to cover those 30 miles. The mouth of the cave is 15 feet wide and difficult to see upon approach. At some point, probably more than 100,000 years ago, a sinkhole collapsed and opened up the cave. Over the millenniums, all manner of creatures wandering the plains stumbled across the opening, only to plunge into the depths of the cave.

The cool temperatures inside the cave – rarely topping 50 degrees F. – are ideal for preserving these fossils, Dr. Meachen says. Her hope is that they have been preserved well enough to extract DNA to compare with similar species that walk the Plains today.

Paleontologists last dug into the depths of Natural Trap Cave in the 1970s and early 1980s. Xiaoming Wang was a graduate student studying paleontology at the University of Kansas at the time and assisted in excavation in 1984, the last year that exploration took place.

"As a fresh student from China, it was a really stunning experience, to say the least," Dr. Wang told the Monitor. "The sheer scale of the cave is quite impressive. It is a vertical drop of more than 80 feet from the cave entrance down to the bottom floor. The width of the cave is about equally as large."

By the time Wang descended into the depths of the cave, researchers had been excavating for several years. Still, he says, he experienced daily discoveries. He recalls the moment he exposed the limb of a bison. In total, those expeditions yielded some 40,000 specimens, which are now housed at the University of Kansas. Wang estimates that those expeditions uncovered only about 10 percent of the cave’s treasures.

Thirty years later, Wang, who is now the curator of vertebrate paleontology at the Natural History Museum of Los Angeles, will return to Natural Trap Cave as part of Meachen’s crew. Many members of the original crews to explore the cave have since died or changed professions. He will be the only member to see the reopening of the cave next Sunday.

“The University of Kansas did the right thing to stop excavations in 1984,” Wang says. “No one could have foreseen the capability of doing ancient DNA sequencing. By preserving those remaining specimens still in the cave, we now have the benefit of being able to extract DNA.”

By the time ancient DNA extraction became a possibility, the previously gathered fossils had sat for more than 20 years in a climate-controlled environment that was ideal for human comfort, but less than ideal for chemical preservation. Researchers were able to extract short mitochondrial fragments from those specimens, but they hope that newly recovered fossils will yield whole mitochondrial sequences and nuclear fragments to enable DNA sequencing. Paleontologists believe this information will provide insights into the lineage of modern animals as well.

While animals roaming the Plains today may appear to be descendents of the Pleistocene giants, there is evidence that suggests they may be more like distant cousins than great-grandparents. Wang is particularly eager to recover the rare American cheetah. These big cats resembled cheetahs found elsewhere in the world, but no one knows for sure if they are real cheetahs or some other cat that independently evolved cheetah-like adaptations.

“That’s a mystery that ancient DNA hopefully can unlock,” Wang says. He and his colleagues don't take that treasure lightly: The team, he says, intentionally will leave much of the cave undisturbed to ensure that future generations of scientists, with yet more advanced technologies, have access to the resources on the site.

However, retrieving the fossils needed to unlock such mysteries is no easy task. The crew will have to rappel 85 feet down to the spot where researchers stopped digging in 1984. Federal officials covered the opening of the hole with a metal grate at that time to deter amateur spelunkers. No new large animals should have fallen in, but a considerable amount of dirt and debris probably managed to slip through the openings over the years. Meachen and her team will have to dig through decades of backfill before the real work can begin.

The crew will rely on a single-rope technique, sometimes referred to as a frog ascending system, to return to the surface. Rope wrenches help bear the climbers’ weight, but the climbers must use their legs to inch themselves up the rope ... eight stories.

“I warned people when I was calling for a crew: This is physically demanding. If you are out of shape or petrified of heights, this is not the dig for you,” Meachen says.

Even in the height of summer, the temperature inside the cave is between 45 to 50 degrees and the humidity is 98 percent. From the time the crew arrives on the scene this Sunday, it will have two weeks to work before it needs to pack up. The crew plans to return for one month each during the summers of 2015 and 2016.

This year's expedition is funded by a grant from the National Geographic Society, and the National Science Foundation will pick up the tab for the next two expeditions.

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