Striking It Rich in Wyoming

By Natalie Angier

Paleontologists unearth a trove of early mammalianfossils

The plains of western Wyoming are today a scarred moonscape of gray hills, but 50 million years ago they were mostly swampland, lush with exotic life. Primitive lemurs swung through palm trees, while the first horse, Eohippus, a short-legged creature about the size of a fox terrier, nibbled on grass beside the squirrelish Paramys.

Now two scientists with the Carnegie Museum of Natural History in Pittsburgh have rooted beneath the sediment of the Wind River valley to unearth a spectacular cache of fossils from the Eocene epoch, that critical time when many progenitors of modern mammals first appeared. Representing some 65 species and including about eight species previously unknown, the bones are the most diverse and perfectly preserved ever discovered from that time. Although they have only just begun to study their find, Richard Stucky, 34, and Leonard Krishtalka, 38, are already convinced that the bones will reveal precious clues to the evolution and extinction of ancient animals. Says Stucky exuberantly: "It's a gold mine."

Wyoming has been a favorite haunt of paleontologists for the past century, ever since westering pioneers reported that many vertebrate fossils were almost lying on the ground. Scientists soon discovered why. Roughly 55 million years ago, the Rockies rose violently, while enormous basins formed around Wyoming. Rains washed sediment into the natural bowls, and thousands of animal carcasses were buried and preserved.

Despite these promising conditions, scientists have rarely found more than a few scattered specimens at a time. But almost as soon as Stucky and Krishtalka struck their pickaxes in the ground last June they unearthed a beautifully preserved Eocene skull and lower jaw of a three-toed dawn horse. Digging further in that spot and five adjacent areas, they retrieved 19 skulls, five eggs, over 150 jaws and hundreds of teeth, limbs and bone bits.

Like the animals from which they came, the fossils are tiny, many smaller than a matchstick. Says Krishtalka: "One rarely finds small specimens preserved so exquisitely." Animals that have been identified include bats, monkeys, iguana-like reptiles, a possum-like marsupial and salamanders. The scientists have yet to label the new species but have linked them to the lizard and shrew families.

Such clues could help researchers better understand life in the Eocene, a time of turbulent change, climatic as well as geological. The earth was slowly cooling, and swamp areas were evaporating. As a result, hundreds of species were dying or seeking warmth farther south. The North American monkeys, for example, migrated to Central and South America. Warmblooded beasts that could adjust to the new cold thrived, among them the forebears of pigs, cows, cats and dogs. For animals, says Stucky, the epoch "was a revolution." And with the bones unearthed for scientists to explore and understand, that revolution continues to reveal its buried secrets. --By Natalie Angler.

Reported by TimothyLoughran/New York

With reporting by Timothy Loughran