Phylogenetic relationships of a new alvarezsaurid (Dinosauria: Coelurosauria) from the Allen Formation (Maastrichtian, Upper Cretaceous) of Río Negro province, Argentina: implications for the argentinian taxa

MESO, JORGE; BAIANO, MATTIA; CANALE, JUAN IGNACIO; SALGADO LEONARDO; CHOINIERE, JONAH; BRUSATTE, STEPHEN

Puerto Madryn

Congreso; Reunión de Comunicaciones de la Asociación Paleontológica Argentina; 2018

Alvarezsauridae is a group of small-sized coelurosaurian theropods, known from Upper Cretaceous deposits of North America, Asia and South America. Although many new alvarezsaurid species have been recently discovered, and the knowledge of their anatomy has largely improved over the last decade, the phylogenetic relationships of Alvarezsauridae are still under debate. The specimen MPCN-PV 738 (previously catalogued as MGPIFD-GR 166/194 and MEPyG-177 by Salgado et al. and Coria et al. in previous works, respectively), from the Allen Formation, sheds some light on that issue. This specimen was included in a matrix of 888 characters and 163 avian and non-avian theropod taxa, and a phylogenetic analysis was performed using TNT. A strict consensus show MPCN-PV 738 nested in a small clade together with Bonapartenykus, with Patagonykus as sister group, all forming a clade recently recognized as Patagonykinae. The autapomorphies that distinguish this new alvarezsaurid are: ventral portion of coracoid strongly medially deflected (less than 120 degrees); anterior sector of transversal ridge on the coracoid robust and wide; grooves and striae only developed on the ventral surface of the coracoid, and dorsally limited by the transversal ridge; coracoid foramen ovoidal, with its major axis anteroventrally-posterodorsally oriented. The synapomorphies that support Patagonykinae are: transversal ridge on the lateral surface of coracoid; coracoid surface decorated with deep and narrow grooves and bumps; recess for the coracoid foramen and pubic apron greatly reduced, restricted to distal end of pubis. These results support previous ideas on the existence of an endemic clade of Patagonian alvarezsaurids.