Fossils

Plastomenus thomasii turtle fossil with slightly disarticulated head and legs. From the Green River Formation.
Plastomenus thomasii fossil

NPS Photo

The fossil record preserved within the Eocene Green River Formation of Fossil Basin is world-renowned. Discoveries of new fossil species from the ancient lake sediments continue to expand understanding of the paleoecosystem.

The quality of fossil preservation is extraordinary, nearly unparalleled in the fossil record. The quiet-water, fine-grained lake sediments, and water conditions that excluded scavengers combined to preserve articulated skeletons (all bones are in place rather than scattered). Delicate fossils, rarely preserved elsewhere, yield valuable scientific data.

Today less than 1% of Fossil Lake is protected and managed by the National Park Service. Fossil Butte National Monument is a site that promotes the protection of this world-class paleontological heritage.

Check out the fossil and donated fossil photo galleries and find more information about the various fossil species of the Fossil Butte Member (FBM) below.
 
 
Diplomystus dentatus fish fossil with deep belly from Green River Formation.
Diplomystus dentatus FOBU791 specimen

NPS Photo

Fossil Fish Species

27 fish species have been identified from the Fossil Butte Member (FBM).
 
Onychonycteris finneyi bat fossil with wings partially outstretched from the Green River Formation.
Onychonycteris finneyi cast of private specimen

NPS Photo

Fossil Mammal Species

10 mammal species have been identified from the Fossil Butte Member (FBM).
 
Boavus idelmani snake fossil partially curled up with head stretched out in an s-curve. From the Green River Formation.
Boavus idelmani cast of private specimen

NPS Photo

Fossil Reptile Species

The 15 species of reptiles identified from the Fossil Butte Member (FBM) include turltes, lizards, crocodilians, and snakes.
 
Aerugoamnis paulus frog fossil with arms and legs spread out from the body. From the Green River Formation.
Aerugoamnis paulus cast of private specimen

NPS Photo

Fossil Amphibian Species

2 amphibian species have been identified from the Fossil Butte Member (FBM).
 
Tynskysagrion brookeae damselfly fossil with white markings near the tips of the dark wings
Tynskysagrion brookeae FOBU448 specimen

NPS Photo

Fossil Arthropod Species

Several arthropod specimens have been identified from the Fossil Butte Member (FBM).
 
Palmites palm frond fossil from Green River Formation.
Palmites FOBU446 specimen

NPS Photo

Fossil Plant Species

Over 400 plant specimens have been identified from the Fossil Butte Member (FBM).
 
Pseudocrypturus cercanaxius bird fossil with bent long legs and disarticulated wings. From the Green River Formation.
Pseudocrypturus cercanaxius cast of private specimen

NPS Photo

Fossil Bird Species

Over 30 species of birds have been identifiefd from the Fossil Butte Member (FBM).
 

If you want to see the data from the fossils collected in the park's research quarry, download the Fossil Lake Quarry Data Spreadsheet (Excel 0.25 MB). If you do not see recent data, check back as the document is updated periodically.

Last updated: September 23, 2022

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