A new genus and species of Pelagornithidae with well-preserved pseudodentition and further avian remains from the middle Eocene of the Ukraine

Abstract

ABSTRACT We describe new avian remains from the middle Eocene of eastern Ukraine. The material includes well-preserved bones of a small species of Pelagornithidae (bony-toothed birds), which was tentatively identified as Odontopteryx toliapica in an earlier study. The Ukrainian pelagornithid is, however, distinguished from this species and other early Eocene pelagornithids in several features, and we describe it as Lutetodontopteryx tethyensis, gen. et sp. nov. The new material includes the most complete pseudodentition of a small Paleogene pelagornithid, and details of pseudotooth morphology strengthen previous assumptions that the pseudodentition of pelagornithids derives from tooth-specific developmental programs and is homologous to true avian teeth on a molecular level. Most major postcranial bones of L. tethyensis are represented by well-preserved bones, and in some derived morphological features the Ukrainian species agrees with Neogene pelagornithids but differs from the early Eocene Dasornis species. We also report a partial sternum of a much larger bony-toothed bird, which resembles the sternum of the middle Eocene Gigantornis eaglesomei. We further describe previously unknown skeletal elements of the loon Colymbiculus udovichenkoi (Gaviiformes), which show that this species substantially differs, in both wing and leg morphology, from the well-known gaviiform stem-group taxon Colymboides.