Well-preserved new skeleton of the Middle Eocene Messelastur substantiates sister group relationship between Messelasturidae and Halcyornithidae (Aves, ?Pan-Psittaciformes)

摘要

A virtually uncrushed skeleton of Messelastur gratulator from the Middle Eocene of Messel (Germany) is described, which for the first time preserves the feet of this poorly known avian species. The new fossil corroborates a close relationship between Messelastur and the early Eocene Tynskya eocaena, from which M. gratulator differs in its more raptor-like feet. The specimen further shows that the Messelasturidae are the sister taxon of the early Eocene Halcyornithidae ('Pseudasturidae'), which are considered to be stem group representatives of the Psittaciformes. A sister group relationship between Messelasturidae and Halcyornithidae is supported by a phylogenetic analysis of 100 morphological characters, but concerning the extant taxa the results of the primary analysis conflict with current hypotheses on avian higher-level relationships. After constraints were enforced, the analysis resulted in a sister group relationship between the Messelasturidae/Halcyornithidae clade and Psittaciformes. Messelasturids have a raptor-like beak and large processus supraorbitales, and were previously considered to be most closely related to either 'falconiform' or strigiform birds. If future data strengthen their psittaciform affinities, they not only add a distinctive new taxon to the stem lineage of Psittaciformes, but also show that some stem group Psittaciformes were predatory birds.