Alvarezsauridae, Cretaceous basal birds from Patagonia and Mongolia.

FERNANDO E. NOVAS

MEMOIRS OF THE QUEENSLAND MUSEUM

Queensland Musum

Año: 1996 p. 675 - 702

0079-8835

Alvarezsauridae represents a clade of bizarre birds with extremely reduced but powerful forelimbs. Twenty synapomorphic features shared by Patagonykus, Alvarezsaurus and Mononykus supports Alvarezsauridae as a monophyletic group of avialan theropods. Diagnostic characters, mainly referred to vertebral, forelimb, pelvic and hindlimb anatomy, emerge from a cladistic analysis of 74 derived features depicting Alvarezsauridae as the sister taxon of the avialian clade Ornithothoraces. Since the origin and early diversification of the Alvarezsauridae probably took place during, or prior to, the Early Cretaceous, their common presence in Patagonia and Mongolia reflects a wider geographical distribution over the world, prior to the development of major geographical barriers between Laurasia and Gondwana during Aptian to Cenomanian times.