On the interrelationships of early Eocene “ parrot-like ” and “ near-passerine ” zygodactyl birds (Aves: Psittacomimidae fam. nov.)

A diverse array of early Eocene zygodactyl birds has been assigned to the Psittacopasseres, the clade including parrots and passerines, but the exact affinities of the fossils are controversially resolved. Here, new analyses are performed based on a revised character matrix. Concerning critical taxa, the results of the primary analysis and that of the analyses constrained to a molecular backbone phylogeny show disparate tree topologies, and probably none correctly reflects the true interrelationships of the fossil taxa.

The new taxon Psittacomimidae fam. nov. is introduced for a clade formed by the taxa Psittacomimus and Parapsittacopes, which were before assigned to the Psittacopedidae. The Psittacomimidae fam. nov. are likely to be the sister taxon of the Parapasseres, that is, the clade formed by the Zygodactylidae and Passeriformes, with the Morsoravidae branching next. A clade formed by all or most Halcyornithidae and the Messelasturidae is termed Messelasturiformes.

A derived morphology of the proximal tarsometatarsus is reported, which may support a clade including the Vastanavidae and Messelasturiformes. However, although psittacopasserine affinities of the Vastanavidae conform to the overall osteology of these birds, the higher-level affinities of the Messelasturiformes are more elusive.