The cranial anatomy of the coelophysoid theropod Zupaysaurus

EZCURRA, M. D.

Historical Biology

Taylor & Francis

Lugar: Londres; Año: 2007 vol. 19 p. 185 - 202

1029-2381

Zupaysaurus rougieri is a theropod dinosaur that is known from an almost complete skull and limited postcranial material (e.g.,axial elements, scapulocoracoid, tibia, astragalocalcaneum), from the Los Colorados Formation (La Esquina Fauna, Norian),NWArgentina. This taxon was originally interpreted as a basal tetanuran, but is actually a member of the Coelophysoidea.Zupaysaurus differs from other basal dinosaurs in the presence of the following cranial apomorphies: a maxillary-jugal ventralmargin describing an obtuse angle in lateral view, a horizontal ramus of the maxilla with parallel dorsal and ventral margins, anotch at the base of the ascending process of the maxilla, and a sigmoid ventral process of the squamosal. Furthermore, theskull of this theropod reveals anatomical novelties (e.g., pneumatic lacrimal, maxillary fenestra, oval orbit, wide contactbetween squamosal and quadratojugal) absent in any other Triassic dinosaur hitherto described, including remainingcoelophysoids. Interestingly, these features resemble morphological aspects of more derived theropods, approaching sometraits of tetanuran and ceratosaurian neotheropods. In this regard, a redescription of the skull of Zupaysaurus and comparisonswith basal neotheropods, mainly coelophysoids, is presented here in order to provide a better cranial anatomical record for thisTriassic theropod and insights to their early cranial evolution.