On the osteology and phylogenetic affinities of the Pseudasturidae – Lower Eocene stem‐group representatives of parrots (Aves, Psittaciformes)

The osteology of the early Eocene (about 50 mya) avian taxon Pseudasturidae Mayr, 1998 is revised and its phylogenetic affinities are analysed. Members of the Pseudasturidae are known from abundant and excellently preserved skeletal material, both complete skeletons on slabs as well as isolated, three‐dimensional bones. Although this taxon is thus among the best represented of all small early Tertiary birds, its systematic affinities were unknown so far. Derived osteological characters which are visible in newly recognized specimens from the Lower Eocene London Clay of England most convincingly support classification of the Pseudasturidae into the Psittaciformes (parrots). Both, in overall morphology and in terms of derived characters, the tarsometatarsus of the Pseudasturidae closely resembles that of the Eocene Quercypsittidae, which were assigned to the Psittaciformes by Mourer‐Chauviré (1992). The Pseudasturidae are considered to be stem‐group representatives of the Psittaciformes and the sister taxon of all other known psittaciform birds. The Eocene taxon lacks the specialized bill morphology of crown‐group Psittaciformes of the Psittacidae. Several other osteological differences between the Pseudasturidae and the Psittacidae probably are also functionally correlated with the specialized feeding technique of the latter. © 2002 The Linnean Society of London, Zoological Journal of the Linnean Society , 2002, 136 , 715–729.