Amid darkness and death, information about the last ice age is entombed at the bottom of a cave
Amid darkness and death, information about the last ice age is entombed at the bottom of a cave in northcentral Wyoming. Here, scientists believe, 20,000 to 25,000 years ago a variety of large mammals died when they were unable to skid to a stop after topping a rise and plummeted 85 feet into what is now called Natural Trap Cave. With the passage of time, the carcasses of a musk ox, saber-toothed lion, a bear twice the size of a grizzly and a cheetahlike cat were fossilized. "It’s a world-class paleontological Pleistocene deposit," said Jim Chase, archaeologist for the Bureau of Land Management’s Cody office. "Essentially it has the entire record of the Pleistocene up until 10,000, 12,000 years ago.The cave is located on federal land managed by the BLM on the western side of the Bighorn Mountains, just south of the deep gouge of Bighorn Canyon National Recreation Area. Over time, the natural trap killed and preserved a diverse cross -section of animals. Inside the cave are the fossilized remains of a bison, mammoth, elephant, deer, antelope and the now extinct dire wolf, which featured a larger head and jaw adapted for crushing bones like the modern hyena. "It’s really one of the better sites in the region in this time period," said Danny Walker, assistant state archaeologist for the Wyoming Department of State Parks and Cultural Resources. The Pleistocene era stretched from 1.8 million to 10,000 years ago, a time when Wyoming may have been similar in appearance to the African savannah, Walker said. Forest intermingled with plains. "There would have been a lot more vegetation," Walker said. "There was more food available for grazing animals, and therefore more carnivores." And the animals were all larger than their modern counterparts. Sometime during this era, Natural Trap Cave formed as water ate away at the limestone bedrock and carved out a cavern. At some point, the roof of the cavern caved in, leaving what is now a 10-foot diameter opening. Eighty-five feet down, the cave opens up into a room roughly 100 feet in diameter. The temperature inside the cave holds steady at a fairly cool 40 to 45 degrees. When the ancient herbivores and carnivores accidentally plummeted into the pit, they died and formed a bone pile somewhat conical in shape. Excavations dated the fossil remains back 100,000 years, but most of the bones are from 11,000 to 20,000 years old.
"Once you’re away from the opening, there’s no more paleontology," Walker said. "It pretty much killed them right there."
Over time, the cool temperatures and minerals in the cave cooperated to preserve the bones.
This unusual bone pile lay largely undisturbed until it was first excavated in 1971 by a student from the University of North Dakota. Three years later, a crew from the University of Kansas dropped into the cave and performed digs every summer from 1974 to ’78.
"That’s pretty much been it," Walker said. "They weren’t able to reconstruct any complete skeletons. But the bone, if you didn’t know it was fossilized, it looked like modern bone."
To preserve the site and protect it from looters, about 30 years ago the BLM erected an angle-iron grate over the opening and locked it shut. The cave is closed to all but authorized scientific investigators.
Chase has been trying for about 15 years to entice another expedition into the cave, but hasn’t had any luck. Logistical problems are probably one of the reasons. Working in the cave requires a light source, scaffolding to climb up and down and constant shift changes to keep everyone warm.
"There is a lot of research about that time period and those mammals that could be done there," Walker said. "But there’s no money."
He added that there is a lot of interest in that era, but so much data and material was collected during the earlier digs that it probably hasn’t all been studied.
"Until there’s a research question, the material is preserved better in the cave," Walker said.