Reassesment of Thegornis musculosus Ameghino 1894 (Aves: Falconidae) based on new material recovered from Santacrucian (Early-Middle Miocene) beds of Patagonia

NORIEGA, JORGE I.; ARETA, JUAN I.; VIZCAÍNO, SERGIO F.; BARGO, SUSANA

Plaza Huincul, Argentina

Jornada; Reunión Anual de Comunicaciones de la Asociación Paleontológica Argentina; 2008

Asociación Paleontológica Argentina

Extant falconids are small to medium-sized predatory birds which occupy all continents except Antarctica, with most of the diversity concentrated in the Neotropics. They have been traditionally grouped with accipitrids as Falconiformes, although some morphological and molecular studies suggest that falconids are not related to accipitrids, but to passerines and parrots, within a larger clade including seriemas. Nevertheless, it is accepted that falconids constitute a monophyletic group. Their fossil record is poor and fragmentary. Extinct representatives from South America include the early-middle Miocene (Santacrucian) Badiostes patagonicus Ameghino and several Pleistocene species of caracaras. Two other Santacrucian species, Thegornis musculosus Ameghino and Thegornis debilis Ameghino were originally described as Falconidae and after moved to Accipitridae Circinae or Buteoninae. Furthermore, Thegornis musculosus was transferred to the extant genus Buteo Lacépède. The discovery of a very well preserved and complete specimen (MPM-PV 3443) of T. musculosus, from the same stratigraphic and geographic provenances of the type material, allowed us to corroborate the validity of the genus and its falconid affinities. It comes from the lower levels of the Santa Cruz Formation at the coast of Santa Cruz Province between Coyle and Gallegos rivers. The cranial morphology and features of limb bones (humerus, tibiotarsus, and tarsometatarsus) exhibit strong resemblances with the living forest-dwelling Micrastur Gray and the open-savannah Herpetotheres Vieillot, but differ substantially from Falconines and Polyborines. Ongoing detailed comparisons with a broad arrange of taxa, will improve our knowledge on the phylogenetic placement, systematics, and ecology of this extinct falcon.