New Fossil Birds from the Earliest Eocene of Mongolia

Abstract

Understanding of the Asian early Paleogene avifauna is limited relative to that of North American and European avifauna of the same period. While major patterns of mammalian faunal exchange among these three regions across the Paleocene/Eocene boundary have been described, much less is known about the dynamics of bird diversity over the same time interval. Here, we report bird fossils from the earliest Eocene Bumban Member of the Naranbulag Formation in central Mongolia that add to the known record from Asia from just after this boundary. Most of this material, collected by the joint American Museum of Natural History/ Mongolia Academy of Sciences expeditions, is referable to a previously described taxon in Presbyornithidae (Anseriformes). However, five isolated elements are identified as comprising at least four species from at least three other major avian clades. While further inclusive phylogenetic analyses of each of these clades are necessary, the new remains represent possible earliest occurrences in Asia of these clades. The material includes a humerus and a furcula from shorebirds (Pan-Charadriiformes), a quadrate from a stem member of the flamingo-grebe lineage (Pan-Mirandornithes), and a coracoid from a stem galliform (Pangalliformes). We also report a humerus with uncertain phylogenetic affinities but with similarities to core Gruiformes. These new fossils expand our knowledge of the Asian avifauna during this time and have the potential to further inform our understanding of the early biogeography of these clades. The shorebird and flamingo-grebe material indicate that both these lineages were present in Asia by the earliest Eocene. The pan-mirandornithine quadrate provides insight into the early feeding ecology of the flamingo-grebe clade.