Fossil Butte

The three fish the panel sets in italics carry nineteenth- and early twentieth-century names. Edward Drinker Cope described Diplomystus and Priscacara in 1877, from localities that included one he called Twin Creek, now known as the Fossil Butte site. Knightia followed in 1907 from David Starr Jordan, who named it for Wilbur Clinton Knight, a University of Wyoming geologist. Two of the three were predator and prey: many Diplomystus are preserved with a Knightia lodged in the mouth, and the larger herring is the second most abundant fish here after the one it ate.

What the plaque says

Fossil Butte Fossil Butte is a 50 million year old lakebed and one of the richest fossil resources in the world. It is part of the Green River Formation, a layer of rock composed of laminated limestone, mudstone, and volcanic ash. Complete paleo-ecosystems are preserved in the formation, which is the geologic remnant of the Green River Lake System of the Eocene era. Designated on October 23, 1972, Fossil Butte National Monument encompasses a part of land that was once under Fossil Lake. Fossil Lake was the smallest and shortest-lived of the Green River System lakes. At its largest size, the lake covered 932 square miles and existed for approximately three million years. One phenomenon of the Fossil Lake fossils is their density. There are as many as several hundred fossilized fish per square meter in some portions of Fossil Butte. At least thirteen genera of fish are found in the sediments of fossil lake, as well as a wide variety of species, from large predators like gar and bowfin to the now extinct Knightia, Diplomystus, and Priscacara. Plant and invertebrate records are equally diverse. Evidence of lily pads, horsetails, ferns, palms, and poplar and elm trees exist along Fossil Lake's floodplain and lower elevations. The remains of dragonflies, mosquito larvae, and water striders bear testament to the vibrancy of this freshwater ecosystem. In addition, evidence of freshwater mollusks, snails, crayfish, and shrimp has been found. The paleontologists who worked at Fossil Butte have deposited specimens at the Field Museum in Chicago, IL, the American Museum of Natural History, in New York City, and Smithsonian Institution's National Museum of Natural History in Washington, D. C.

Where it stands

Worth the stop nearby

• Fossil Butte National Monument — 7.4 mi
  The floor of a 52-million-year-old lake, packed with whole fish, the oldest complete bats and the only complete freshwater stingrays.

More markers nearby

• Oregon Trail Memorial (Kemmerer) — 4.9 mi
• Coal Miner Memorial — 5.2 mi
• Old Oregon Trail (Cokeville) — 25 mi
• Tri State Survey Monument — 25 mi