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Green River Formation Fossils

The Fossil Lake Safari quarry is in the Fossil Butte Member of the Green River Formation.  The fossils unearthed in this area thrived in and around a vast freshwater lake that covered parts of SW Wyoming during the early Eocene, approximately 52 million years ago. Renowned globally for their variety, quantity, and exceptional preservation, these fossils owe their remarkable state to the distinctive conditions of Fossil Lake.  

At this time 27 species of fish, 30 species of birds, 15 species of reptiles, 10 species of mammals and over 400 types of plants have been described from the Fossil Butte Member of the Green River Formation.  Below is a partial list of some fossils that visitors might encounter in the Fossil Lake Safari quarry near Kemmerer, Wyoming.

Unless otherwise noted we have used photos from specimens collected at the Fossil Lake Safari quarry on this page. Most of these were collected by Warfield Fossils and Rick Hebdon.


Being an ancient lake, Fossil fish are the primary type of fossils found in the quarry. The species range from being extremely abundant to species where only a single example has been found.


Reptiles including turtles, crocodiles, snakes and lizards are extremely rare fossils in the Green River Formation. There might be a handful of reptile fossils found each year across all of the quarries operating in the Green River Formation.


The Green River Formation has yielded some of the world’s most exquisitely preserved bird fossils. These avian specimens offer an unparalleled window into an entire ecosystem frozen in time, granting us a rare glimpse into life over 50 million years ago during the Early Eocene epoch.

This period marks a critical juncture following the mass extinction at the end of the Cretaceous period, which wiped out 75% of all species.  This includes the dinosaurs, with the exception of the lineage that would eventually evolve into modern birds.  The fossil record from Fossil Lake illuminates the diversification of these early avian inhabitants.

34 different bird species, representing at least 27 distinct families have been uncovered from the Fossil Lake deposits.  These findings encompass a diverse array of species, including frigate birds, parrots, jacamars, mousebirds, and many others. More of these important bird fossils have been uncovered in the Fossil Lake Safari quarry than at any other site in the Green River Formation.  That said, complete birds are very rare fossils, with maybe one being found found on average per season at the quarry. Individual feathers or parts of birds (possibly torn apart by predatory turtles) being found more frequently.


The Green River Formation is possibly the most important Eocene mammal locality in the world, because specimens can be found complete and articulated while most sites only produce individual bones and teeth. Mammal fossils are extremely rare and include the earliest known bats, otter-like animals, rodents, tapirs and primitive horses.

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