(Reuters) - Scientists will begin excavation early next week of an ancient Wyoming sinkhole containing a rare bounty of fossil remains of prehistoric animals, such as mammoths and dire wolves, preserved in unusually good condition, researchers said on Thursday.

   The two-week dig, set to begin next Monday under the direction of Des Moines University paleontologist Julie Meachen, marks the first exploration of Natural Trap Cave in north-central Wyoming since its initial discovery in the 1970s.

At that time, scientists found that the 85-foot-deep cavern formed a natural repository for a rich fossil record that may date back as far as 100,000 years, but a full-scale expedition into the sinkhole has not previously been attempted.

  The cave, formed by the collapse of limestone bedrock at the base of the Bighorn Mountains, became a tomb for thousands of ancient mammals that stumbled into the 15-foot-wide mouth of the sinkhole, then concealed by vegetation, and plunged to their deaths.

  Conditions in the underground chasm, which widens to 120 feet at its base, are cold and damp, offering a degree of preservation for fossils generally associated only with those found frozen in ice in Siberia and the Arctic, Meachen said.

  "They fell into a refrigerator," she said of animals such as camels, American lions, cheetahs, woolly mammoths and short-faced bears.

  Meachen will lead a team of international scientists as they rappel from the outer rim of the cave's opening – covered for decades by a metal grate installed by federal land managers – to the depths below, where they will load fossils into buckets to be hoisted to the surface.

  Analysis of recovered fossils is expected to provide new insights into the climate, diets and genetic diversity of North American mammals that disappeared during the Ice Age extinction of more than 10,000 years ago.

   Meachen said there may also be an opportunity to draw inferences tied to an emerging theory that the mass extinction was linked more to overhunting by humans, whose appearance in North America coincided with a die-off long thought to be influenced mostly by climate.

  Meachen said she had trained at a rock-climbing gym for the descent and the more arduous ascent, also by rope, but remained leery of entries and exits from the cave.

  "I'm scared out of my wits," she said.

 

(Reporting by Laura Zuckerman from Salmon, Idaho; Editing by Curtis Skinner, Steve Gorman and Clarence Fernandez)