New information on the cranial and vertebral anatomy of Buitreraptor gonzalezorum (Theropoda, Unenlagiinae) and preliminary comparisons with other South American unenlagiines

F.A. GIanechini, S. Apesteguía and P.J. Makovicky

Within the framework of a doctoral thesis about the small theropods coming from the Cerro Policía area (Candeleros Formation, Río Negro Province), novel information of Buitreraptor gonzalezorum Makovicky, Apesteguía and Agnolín 2005 is presented here, including partial comparisons with other unenlagiines. Shared cranial characters between Buitreraptor and Austroraptor cabazai Novas, Pol, Canale, Porfiri and Calvo 2009 include: skull exceeding femoral length by 25%; low anterior process of maxilla; large maxillary fenestra not dorsally displaced; more than twenty maxillary and dentary teeth; fluted teeth without serrations and without basal constriction; groove on the dentary containing a row of nutrient foramina. Otherwise, Buitreraptor differs from Austroraptor in having a larger maxillary fenestra; elongated frontals with dorsal depressions; triangular postorbital; compressed teeth, with an 8-shaped basal section. Concerning vertebral features, Buitreraptor has a ventral faint keel on the axis (not comparable with other unenlagiines); elongated medial cervicals; epipophyses on all cervicals; carotid process on the latest cervicals; ventrolateral ridges on the last cervical culminating posteriorly as small tubers; neural spines of the dorsals without distal spine tables (this latter feature invalidates a proposed synapomorphy for Unenlagiinae). Additionally, whereas pleurocoels are restricted to anterior dorsals in Buitreraptor (and probably in Austroraptor), in Unenlagia comahuensis Novas and Puerta 1997 they are in anterior and posterior dorsals; and the foramina that pierces the base of the neural spines in the latter are absent in the two former. This analysis increases the knowledge of the anatomy of Buitreraptor and shows a high internal variability among unenlagiines

Fuente: XXV Jornadas Argentinas de Paleontología de Vertebrados, San Luis, 2010.