A new species of the Prophaethontidae (Aves, Phaethontiformes) from the early Eocene London Clay

Mayr, Gerald; Kitchener, Andrew C

A new species of the Prophaethontidae (Aves, Phaethontiformes) from the early Eocene London Clay

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Mayr, Gerald

Kitchener, Andrew C

ORCID

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October 29, 2024

Abstract

We report new specimens of the stem group phaethontiform Prophaethon from the early Eocene London Clay of Walton-on-the-Naze (Essex, UK). The two partial skeletons are distinctly smaller than a previously described record of Prophaethon from this locality, which was assigned to P. shrubsolei. Even though some extant aquatic birds show a pronounced sexual dimorphism in size, this is considered unlikely to explain the size disparity of the Prophaethon fossils from Walton-on-the-Naze and the new specimens are here described as P. waltonensis, sp. nov. The distal end of the humerus of the new species differs from that of other Phaethontiformes in the presence of a small but well-defined processus supracondylaris dorsalis. With regard to this feature, it shows a resemblance to the humerus of the Procellariiformes, which is unexpected in light of the recently proposed hypothesis that the sister taxon of the Phaethontiformes are the terrestrial Eurypygiformes. Finally, we comment on prophaethontid remains from the late Paleocene of Kazakhstan, which were assigned to the taxa Zhylgaia Nessov, 1988 and Tshulia Nessov, 1988. We synonymise the latter with the former taxon and also consider it possible that Zhylgaia Nessov, 1988 is a junior synonym of Prophaethon Andrews, 1899.