The galliform birds from the Lower Eocene London Clay of Walton-on-the-Naze (Essex, U.K.): New species suggest faunal connections to Asia

Abstract

ABSTRACT We report stem group Galliformes from the lower Eocene (Ypresian) London Clay of Walton-on-the-Naze (Essex, U.K.), which are among the oldest known fossils of galliform birds. The specimens are assigned to two new species, ?Paraortygoides argillae, sp. nov. and Waltonortyx bumbanipodiides, gen. et sp. nov. The latter is classified in a new family-level taxon, Waltonortygidae, fam. nov., which differs from other higher-level clades of stem group Galliformes in a proximo-distally narrow caput humeri and a short tuberculum dorsale of the humerus. With regard to these plesiomorphic features and a characteristic morphology of the coracoid, Waltonortyx is similar to early Eocene stem group Galliformes from Mongolia. Wing and pectoral girdle bones of a third, undetermined galliform from Walton-on-the-Naze resemble the Quercymegapodiidae; this fossil also shows a similarity to early Eocene galliforms from Mongolia. The affinities of “Paraortygoides” radagasti Dyke and Gulas, 2002, the only previously described putative galliform from Walton-on-the-Naze, are uncertain and neither its classification in the Galliformes nor its assignment to the taxon Paraortygoides are unequivocally established. For the first time we subjected a larger taxonomic sample of early Paleogene Galliformes to a formal analysis, and even though the resulting phylogenies were poorly resolved, they supported paraphyly of the Quercymegapodiidae, with the Early Miocene taxon Ameripodius being more closely related to the crown group than the late Eocene species of Quercymegapodius. Waltonortyx bumbanipodiides was recovered as the sister taxon of the Mongolian Bumbanipodius transitoria, which indicates early Paleogene dispersal events across the Turgai Strait.