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Wyoming national parks

Photo: Arvid Aase/National Park Service

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Fossil Butte

Some of the world's best preserved fossils are found in the flat-topped ridges of southwestern Wyoming's cold sagebrush desert in Fossil Butte National Monument. Fossilized fish, insects, plants, reptiles, birds and mammals are exceptional for their abundance, variety and detail of preservation. To wit: this Procambarus primaevus crayfish, which lived in the shallow, near-shore water of Fossil Lake. Its closest living relative, Austrocambarus, is found in Mexico.