Fossil Amphibian Species

Amphibians are extremely uncommon fossils in the Fossil Butte Member (FBM). Only 2 species have been identified. One possible explanation for this scarcity of amphibians is the alkalinity of Fossil Lake's water. The lake was supersaturated with calcium carbonate, making the pH around 8 or 8.5. Amphibians generally prefer a neutral pH of 7. It is possible amphibian specimens washed into Fossil Lake from a connecting stream with a neutral pH.

See what amphibian fossils are on display in our museum exhibits.
Paleoamphiuma tetradactylus fossil salamander with tiny fore and hindlimbs visible. It is missing a hindlimb. From Green River Formation.
Paleoamphiuma tetradactylus, catalog number FOBU20833

NPS photo

Aquatic Salamander - Paleoamphiuma tetradactylum

Order Urodela, Family Sirenidae
The 4 modern species of the Sirenidae family (commonly known as sirens) are found in warm climates of the southeastern United States and northern Mexico. Sirens are the only omnivorous salamanders, the rest being strict carnivores.

Like its living relatives, P. tetradactylum had a toothless jaw and very small front limbs. However, modern sirens totally lack hind limbs, unlike P. tetradactylum. The specimen pictured is approximately 9.6 inches long.
Aerugoamnis paulus fossil frog with arms and legs spread out. From Green River Formation.
Aerugoamnis paulus Fossil Butte National Monument specimen

NPS Photo

Frog - Aerugoamnis paulus

Order Anura, Family Anomocoela
Anura species are amphibians lacking tails, such as frogs. Only two specimens of this species have been found in the FBM.

Last updated: January 31, 2024

Park footer

Contact Info

Mailing Address:

P.O. Box 592
Kemmerer, WY 83101


307 877-4455

Contact Us