PRIMOBUCCO MCGREWI (AVES: CORACII) FROM THE EOCENE GREEN RIVERFORMATION: NEW ANATOMICAL DATA FROM THE EARLIEST CONSTRAINED RECORDOF STEM ROLLERS

摘要

The Eocene Green River Formation provides one of the richest records of fossil birds worldwide. As part ofa reevaluation of this avifauna, we describe 12 new specimens of the stem roller Primobucco mcgrewi from the well-dated(51.66 + 0.09 Ma) Fossil Butte Member (FBM) of the Green River Formation of Wyoming. FBM specimens represent mostof avian diversity in the Green River Formation and include the oldest well-constrained record of the roller lineage (Coracii).These fossils provide new anatomical data, including the first observations on the palate, and broaden our understanding ofthe distribution, abundance, and taphonomy of P. mcgrewi. Using museum records and lithological comparisons, 14 of the15 known P. mcgrewi specimens can now be assigned to specific quarries within Fossil Lake. The species is now known fromfive distinct localities representing both nearshore and mid-lake environments and accounts for >10% of the 148 FBM avianspecimens reviewed in this study. Pectoral elements are disproportionately represented in the FBM P. mcgrewi specimens,and more than half of the sample exhibits broken elements. These new fossils and other key specimens from the Eoceneof North America and Europe clarify our understanding of the evolution of the clade Coracii. Extant parts of this lineage(i.e., Coraciidae and Brachypteraciidae) have specialized ecologies and restricted Old World distributions, whereas stemrepresentatives appear more generalized and were a major component of some North American avifaunas.