Fossil Lake’s Legacy at Wyoming’s Fossil Butte

September 28, 2022


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Photographer: Ray Boren 

Summary Author: Ray Boren 

Over 50 million years ago — during the Eocene Epoch, after the age of dinosaurs and as a result of the rise of the Rocky Mountains — a freshwater lake formed in western North America, covering an area that today is partly in southwestern Wyoming, northern Utah and a bit of Idaho. Geologists and paleontologists call the vanished body of water Fossil Lake, because its sediments, rich in calcium carbonate, excellently preserved the remains of prehistoric fish, birds, mammals, reptiles, amphibians, insects and subtropical plants, such as ferns and palm trees. The U.S. National Park Service’s Fossil Butte National Monument, west of Kemmerer, Wyoming, encompasses just a fraction of Fossil Lake’s now-uplifted territory, and the displays in its visitor center showcase the rediscovered diversity of life (top photo). Fossil displays include lizards, snakes, small extinct mammals, a couple of bats, a caiman, and at the bottom left, a typically small early horse (Protorohippus venticolum) of the Eocene — member of a taxonomic family that subsequently disappeared from the continent upon which it evolved.

In the 2nd photograph, my great-nephew, Hunter, is standing inside Fossil Butte’s visitor center next to a much-fractured 13-foot-long (4 m) cast of a crocodilian fossil, Borealosuchus wilsoni. A third image (bottom), taken along the park’s scenic drive, presents the eroded, and sometimes slumping, buttes and slopes of the Green River Formation, in which the fossils are quarried. 

The Fossil Butte area also played a part in the fabled “Bone Wars,” or “Dinosaur Wars,” of the late 19th century. Naturalists and scientists made note of early fossil finds during the era’s exploratory mapping and transcontinental railroad surveys. Rival paleontologists Othniel Charles Marsh and Edward Drinker Cope were famously among the scientists and professors who vied in discovering and describing fossils. They and others often hired individuals and teams to dig and gather fossils for them, which were sent to universities, laboratories and museums. Fossil Lake specimens made their way to scientists and collectors in the Eastern United States and around the world, a process that continues today from quarries on state and private land. Photos taken on August 1, 2022.


Fossil Butte National Monument, Wyoming Coordinates: 41.8563 -110.7625

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