A new species of Threskiornithidae-like bird (Aves, Ciconiiformes) from the Green River Formation (Eocene) of Wyoming

ABSTRACT

A new avian species from the late early Eocene Fossil Butte Member of the Green River Formation is described based on a nearly complete postcranial skeleton. The new species, Vadaravis brownae, gen. et sp. nov., can be diagnosed by a unique combination of characters, including the following autapomorphies, which are unique among Aves: two (cranial and caudal) small and discrete pneumatopores on the lateral sides of the caudal-most thoracic centra; and a caudoventrally located pisiform process of the carpometacarpus that projects only weakly cranially. Phylogenetic analyses recover Vadaravis as a member of the waterbird assemblage (including, e.g., penguins, storks, pelicans), closely related to taxa traditionally placed within the avian order Ciconiiformes (storks, flamingos, herons, the hamerkop, ibises, and spoonbills). Additional morphological features and a phylogenetic analysis constrained by a recently recovered waterbird topology suggest close affinities between Vadaravis and Threskiornithidae. This new species represents the first proposed part of Ciconiiformes (and possibly stem-Threskiornithidae) in the Green River Formation of North America. Its discovery increases the known taxonomic and ecological diversity of this diverse fossil avifauna. Vadaravis also represents one of the oldest members of Ciconiiformes (and possibly stem-Threskiornithidae), and implies that additional lineages within the waterbird assemblage had diverged by the late early Eocene.

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ACKNOWLEDGMENTS

N.D.S. was supported by funding from NSF ANT-0838925, NSF DEB-0808250, the Field Museum of Natural History Brown Family Graduate Fellowship, and AMNH Frank M. Chapman Memorial Fund during this project. In particular, we would like to thank B. Brown and R. Brown for their support of this project and Field Museum research and collections in general. This project was also supported by grants NSF EAR-0938199 to J.A.C. and NSF EAR-0719943 to L.G. W. Simpson is thanked for collections support at FMNH and for assistance operating and optimizing the FMNH Geology Department X-ray imaging machine. C. Van Beek (FMNH) performed additional preparation on FMNH PA 718. We also thank D. Willard and M. Hennen for access to FMNH collections; and T. Chesser, J. Dean, M. Florence, H. James, and S. Olson for assistance and collections support at USNM. For assistance and support on this project, as well as discussion on various manuscript drafts, we thank M. Coates, D. Ksepka, S. Hackett, P. Makovicky, and N. Shubin. The final version of the manuscript benefited greatly from the reviews of D. Ksepka, J. Nguyen, and Editor T. Worthy.

Handling editor: Trevor Worthy