Fossils reveal 'missing links' in Earth's evolution after dinosaurs
4 July 2013 Last updated at 04:00 BST
What is now a dry, harsh mountain desert in south-west Wyoming was once a lush subtropical landscape with lakes, volcanoes and an abundance of wildlife.
In "The Lost World of Fossil Lake", Lance Grande, the distinguished service curator at the Field Museum in Chicago, takes us back more than 50 million years to reveal how North America developed in the period after the extinction of the dinosaurs.
He says that paleontologists always search for "missing links" in natural history, and in Fossil Lake, they find clues as to how today's world emerged all the time.
Researchers have collected prehistoric remnants from Fossil Butte, one of the world's richest fossil depots, since the so-called Bone Wars 150 years ago, when Edward Drinker Cope and Othniel Charles Marsh raced to become the top paleontologist of their time.
Mr Grande, a lecturer at the University of Chicago and adjunct professor at the University of Illinois, spoke to the BBC about his own decades-long work at the site.
Produced by the BBC's Sune Engel Rasmussen; edited by Bill McKenna
Photographs courtesy of Lance Grande and John S Weinstein