I’ve been hooked on paleontology ever since this trip. I don’t mean that I love the dirty and painstaking work of actually uncovering bones and fossils and trying to figure out what and how old they are, but the excitement of seeing discoveries made in exotic locales and learning about how these animals lived and died. I’m afraid that makes me a bone-digging voyeur.
AUGUST 1975 — The western foothills of Wyoming’s Big Horn Mountains are arid, red and rocky, peppered by clumps of pungent sage brush and dwarfed juniper trees.
A few cattle graze on the sparse grass, and an occasional deer bounds through a ravine, but the harsh terrain supports few animals.
It wasn’t always so desolate. In the Pleistocene Epoch, 10,000 years ago and earlier, the Big Horn foothills teemed with large mammals. It was a wetter climate. The seasons were more moderate, the land more lush and more forested than today.
Herds of bison, horses and camels grazed on the meadows, stalked by fleet, long-legged bears and cats. Mammoths lumbered through the valleys. Bighorn sheep cropped hillside grasses.
The hills are limestone and pocked with caves and hollows. One cave mouth was open to the sky at the end of a finger of land, affording no escape for a panicking herd pursued by a fast-moving predator. This narrow peninsula was flanked by canyons which funneled predator and prey toward a rise, and then they all plummeted into the hole. Hungry wolverines and jackal-like dire wolves, catching a tempting whiff of rotting meat, crept daringly on a ridge of melting snow along the edge and tumbled below.
As thousands of years passed, the cave gathered a scrambled mass of victims, preserved in layers, until a severe change in the climate wiped out most of the large mammals above, ending the cave’s carnage.
Today (1975), paleontologists and anthropologists from the University of Kansas and the University of Missouri – Columbia are making an easier descent to the bottom of the cave to return the bones of those Pleistocene animals to the surface, where they become the survivors of their age.
The hole, known as the Natural Trap, is a vast 85-foot-deep dome-shaped limestone cavern (karst sinkhole). Tens of thousands of years ago part of the cavern’s roof fell in, making it a death-trap.
The names of the Pleistocene mammals in the trap may sound the same as some of the modern-day Big Horn animals — bighorn sheep, bison, bear — but the Pleistocene specimens were larger, different animals. The Pleistocene versions often had longer legs. The modern counterparts of other animals also found in the Natural Trap are smaller, such as wolves, wolverines and pronghorn antelope. Other animals found in the Trap, such as horses, camels, American lion, mammoth, woodland musk ox and American cheetah, all went extinct at the end of the Pleistocene.
“I don’t think we have a good potential in a specimen from the cave that is a good ancestor of any animal now in the area, ” Dr. Martin said.
Humans, who hunted the large Pleistocene mammals for food, partly has been blamed for their extinction, but most of the evidence points to climatic change as the cause, not only in North America but world-wide, Dr. Martin said.
The paleontologists are studying soil samples and bone deposition, looking for clues to the climatic fluctuations of the past, useful in anticipating future climate changes. The types of animals found in the trap probably will indicate the climate at the time since animals migrate to their favorite climates, Dr. Martin said.
The specimens from the trap went to K.U. Museum of Natural History, which has the tenth largest vertebrate paleontology collection in the country.
There have been some remarkable finds, such as the cheetah-like cat, which has the characteristically long radius and ulna limb bones of the modern-day cheetah and has been found nowhere else in North America, Dr. Martin said.
“The cheetah-like cat found in the cave is the first good evidence that there was one in North America,” Dr. Martin said. There were several cheetah-like cat specimens found in the trap with the small cheetah canine teeth, necessary to give more space in the nose area. To run as swiftly as it does, the cheetah requires a large lungful of air.
The short-faced bear specimen is one of the most spectacular finds do far (as of August 1975), Dr. Martin said. The beat was a long-legged open country animal, adapted for running and more carnivorous than modern-day bears. (A fight between a short-faced bear Arctodus simus and an American lion Panthera atrox near the Natural Trap is featured in episode nine of the History Channel’s “Jurassic Fight Club” in 2008.)
The bones of horses are the most abundant specimens found. Many seemed to have landed on their feet, snapping their leg bones. The cave’s fine limestones preserved the bones well, but most were broken from the initial impact or later by roof fall and other carcasses. To find the bones fragment, the crew sieves all of the dirt from each five-by-five section. The pieces are then painstakingly washed, scrubbed with toothbrushes and sorted at camp. Some are glued there, the rest to be assembled at K.U.
Temporary scaffolding is erected and dismantled each summer, the most dangerous part of the expedition, Dr. Gilbert said. The group couldn’t afford permanent scaffolding. Many team members prefer to drop into the cave by rappelling, which was the only way to enter the cave before 1974. There is a natural ledge just below the cave opening from which it’s easy to rappel. Climbing out by jumaring on a rope is a much more strenuous exercise, so everyone climbs up the shaky scaffolding to get out of the cave.
The scaffolding rests in a depression where deposits continually are eroded by rainfall even though the annual precipitation averages less than 15 inches. Bones remain intact in a mound to the east of the scaffolding where the crew lie on their sides and stomachs picking at the dirt, ice picks and whisks brooms. Dig sites were selected at random until a few productive sections were located.
There are possibly 30 feet of deposits to excavate, Dr. Gilbert said. Specimens could be as old as 50,000 years at the bottom, but there’s no way to tell except to dig there.
“I personally don’t want to dig the entire cave,” Gilbert said. “I’d like to leave a third or half of it for the future to investigate when they have better technology to understand it.”
George Blasing’s Blog “Dinosaur George” is on my blogroll at the right.