A remarkably complete skeleton from the London Clay provides insights into the morphology and diversity of early Eocene zygodactyl near-passerine birds

Abstract

Recognition of the zygodactyl parrots (Psittaciformes) as the closest extant relatives of passerines (Passeriformes) shed new light on the affinities of various Paleogene birds with a zygodactyl foot, which are now considered to be stem group representatives of the Passeriformes. However, most of these taxa are known only from compression fossils, which allow the recognition of a limited number of osteological details. Here, an exceptionally complete skeleton of a new species is described from the early Eocene London Clay of Walton-on-the-Naze (Essex, UK). Parapsittacopes bergdahli gen. et sp. nov. resembles Psittacopes lepidus (Psittacopedidae) from the Messel fossil site in Germany, from which it is distinguished in beak shape and several postcranial characters. Even though the phylogenetic analyses yielded conflicting tree topologies under different settings, all of the resultant phylogenies supported close affinities between Parapsittacopes, Psittacopes and the Eocene taxa Pumiliornis and Morsoravis. The three-dimensionally preserved bones of the P. bergdahli holotype exhibit subtle osteological characteristics of passeriform birds, which have not been reported from previously known fossils of closely related zygodactyl stem group taxa. The broad beak and low mandibular rami indicate that P. bergdahli may have caught insects by sallying flights from perches, and the new species therefore adds another feeding adaptation to the already diverse array of zygodactyl stem group Passeriformes with disparate feeding ecologies. http://zoobank.org/urn:lsid:zoobank.org:pub:FD0E9DC4-961F-4460-9466-164E5EB42E4E