A NEW FOSSIL GALLIFORM FROM THE BRIDGER FORMATION (EOCENE: 50-48 MA), SOUTHWESTERN WYOMING

A new fossil galliform (Aves, Galliformes) recovered from the Q-level of the Bridger Formation (Bridgerian: 50-48 Ma) highlights the importance of this middle Eocene rock unit in documenting the taxonomic and geographic radiation of avian paleofaunas. The Bridger Formation represents a mixture of fluvial (volcaniclastic sandy channel fills and associated overbank deposits) and lacustrine units (carbonates, shales, and distributary mouth bar and channel fill deposits). Vertebrate fossils are typically preserved in either channel fills or overbank deposits, providing information on the region’s aquatic and terrestrial communities. Periodic influx of volcanic ash from the north (both airborne and fluvially transported) may have caused local mass mortalities and aided in the preservation of smaller, fragile skeletal elements that are normally destroyed by subaerial exposure or fluvial processes. Because of these unique taphonomic conditions, this specimen of galliform (AMNH 30331) is well preserved and relatively complete compared to most Eocene avian material. The described fossil record of Galliformes appears extensive if taken at face value: putative remains of these birds have been described from the latest Cretaceous (68-65 Ma) to the Recent. However, the majority of specimens utilized to designate a new taxon is often extremely fragmentary and/or poorly preserved. The completeness of this specimen holds great promise for the study of phylogenetic relationships among Galliformes and a cladistic analysis, performed with the inclusion of this specimen, sheds new light on the tree topology of galliforms.