Isolated feathers are the most commonly found bird fossils in Green River deposits. Some feathers are so large that they indicate a giant bird once lived at Fossil Lake, although no skeletons have yet been discovered.
The largest example pictured here (bottom) may have belong to the giant ground bird Gastornis, which stood over six feet in height and possessed powerful legs, large taloned feet, a massive head, and a fearsome beak several times larger than that of an ostrich.
These huge birds may have fed on mammals and other vertebrates. As predators, they would have been at the top of the food chain around Fossil Lake, because large carnivorous mammals hadn't yet evolved.
Specimens: (Top Left) FMNH PA727, (Top Middle) FMNH PA785, (Top Right) FMNH PA 784 (Bottom) FOBU 13445A, feather possibly from Gastornis, closely related to Galloanserae
Locality: Fossil Butte Member of Green River Formation
Credit: Photo courtesy L. Grande