For the first time in more than 30 years, palaeontologists are preparing excavate a sinkhole-type cave in northern Wyoming that contains the ancient remains of tens of thousands of animals.
Those animals include American cheetahs, mammoths and short-faced bears - species now extinct that were common more than 20,000 years ago. Over many years, tens of thousands of animals accidentally fell into the pit and died.
Natural Trap Cave is a 15ft-wide hole in the ground that opens up into an 85ft-deep cavern. Starting on Monday, scientists plan to resume digging in Natural Trap Cave for the first time since the early 1980s.