Descent into an ice-age bonebed in Wyoming

The giant pit may hold clues about the demise of the West’s ancient megafauna.


Seeking to escape the blazing sun, a packrat ducks into a Wyoming cave. This is a mistake: The unfortunate rodent plunges 85 feet, smashing on the rocky floor. It’s hardly the first to misjudge the cavern, a yawning pit near Lovell, Wyoming. Unwary stilt-legged horses, American lions, false cheetahs, wolves, bighorn sheep, camels and even mammoths were tumbling in here some 100,000 years ago. There’s a reason it’s called Natural Trap Cave.

A week later, I am following in the packrat’s footsteps, in the company of the first expedition to visit the cave in 30 years. University of Iowa paleontologist Julie Meachen and two others lead the way, clambering through the grate hatch. My heart pounds as I peer after them into the dark. Still, I descend the short ladder, my climbing gear clanging against each rung.

At the bottom waits spelunker Juan Laden, a former search-and-rescue specialist who heard about the expedition and drove up from Lander on a whim, then stayed to oversee safety. He gently guides me through various knots and riggings, and I take a deep breath, sit back in my harness and let go. “You’re the first one to do the swing thing,” Laden says as I pendulum out over the void, “but that’s OK.” And just like that, it stops being scary; my descent to the floor is surprisingly slow and controlled.

Meachen pulls me by the boot to solid ground. The air smells of damp earth, and its 42 degrees come as a relief after the day’s 90-degree heat. The tan and orange rock walls glow faintly in a shaft of sun falling from the cave’s mouth.

That light also finds the packrat. Meachen introduces me: “This is our mascot, Packy Le Pew. We named him that because after a few days, he started to stink a little.” During the ice age, the smell here must have been horrific, making the cave irresistible to scavengers and predators, whose remains have been uncovered in numbers greater than usual for an ice age bonebed. Meachen leads me to an innocuous patch of soil. I had imagined a great pyramid of megafauna skeletons, but most of the chocolate-colored bones are scattered through a moist slurry of sediment and rock that requires nothing more than a dental pick to excavate.

I click on my headlamp, grab a small screwdriver and settle onto a foam mat next to San Bernardino County Museum paleontologist Eric Scott, an expert on prehistoric horses. No sooner do I get into place than I notice a long thin triangle of bone. “Do you know what that is?” Scott excitedly asks, before answering himself. “That’s a horse splint!” — a tiny leg bone that’s a remnant of the additional two toes earlier horses trotted around on.

Georgia Tech paleontologist Jenny McGuire has even better luck. Every few minutes, she stops her scraping to call out a new bone, and the other paleontologists gather round to ogle parts of camel, horse, wolf.

But the expedition’s real quarry is much, much smaller: tatters of ice age genes. Meachen, the excavation leader, has teamed with Alan Cooper, a specialist in ancient DNA at the University of Adelaide, to search for genetic clues indicating how the West’s megafauna were faring long before the climate warmed and humans appeared on the scene and killed them off. Were they thriving, or already in decline? The refrigerator-cool of the cave has likely preserved some of their genes, locked in bone that Cooper drills out with a Dremel and packs in coolers, to analyze back home in Australia.

Cave specialist Brian McKenzie descends into Natural Trap Cave to clear out wood and scaffolding from previous excavations.
Courtesy Bureau of Land Management

The answers will take years to tease out, but my time here is over. The thought of the harness’ squeeze reminds me to empty my bladder, which I do according to cave protocol — peeing into an empty orange juice bottle to avoid adding my own DNA to the ancient remains. Then I shimmy back into my gear, determined to jig up under my own power. Returning to the sunlight never felt so good.

The next day is also the excavation’s last. The crew places a cage over Packy Le Pew so that, next year, he can demonstrate firsthand how the cave breaks down bodies, as his bones slowly join those already here. The cave is not always merciless, however: When a deer mouse tumbles through its maw, it miraculously survives. The team brings it up to the surface, gives it an almond and some water, and soon it scurries off into the sage — joining the scientists as one of the few mammals to escape Natural Trap.

This story was originally titled "Descent through time" in the print edition.

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