Cranial Osteology of the Theropod Dinosaur Incisivosaurus gauthieri (Theropoda: Oviraptorosauria)

Abstract

We provide a description of the holotype skull of the unusual oviraptorosaur Incisivosaurus gauthieri. Previous phylogenetic analyses have placed this taxon firmly within Oviraptorosauria near the base of the clade; however, until now only a cursory description of this important specimen was available. The presence of many primitive characteristics (e.g., maxillary and dentary teeth as well as an extended palate and rostrum) indicates that the observed similarities between avians and derived oviraptorids are convergences rather than shared derived characters. In addition, we clarify previous descriptions of several ambiguous anatomical features, most notably of the palate. We also employ computed tomographic (CT) analysis, which allows for a more complete description of the braincase and the reconstruction of an endocranial endocast. CT imagery reveals features that were before unobtainable, such as the presence of a replacement tooth behind the large rodentiform incisor in the premaxilla. This arrangement indicates that although the incisiform teeth of I. gauthieri are morphologically distinct they are replaced in typical archosaurian fashion.

Cranial anatomy ofErlikosaurus andrewsi(Dinosauria, Therizinosauria): new insights based on digital reconstruction

“…Basipterygoid processes and basal tubera are absent, similar to the condition in oviraptorosaurs (Clark et al, 2002;Balanoff et al, 2009). As a result, the external basisphenoid and basipterygoid recesses, which are common in more basal theropods (Witmer, 1997), are absent in E. andrewsi.…”

“…CT scans indicate the absence of a suture, but a series of breaks pervade the bone obscuring finer details. Parietal fusion occurs in various basal theropods (Coria and Currie, 2002;Brusatte and Sereno, 2007), oviraptorosaurs (Clark et al, 2002;Balanoff et al, 2009), and troodontids (Makovicky and Norell, 2004). The main body of the parietal, forming a large part of the caudal skull roof, is approximately horizontal and dorsoventrally flat.…”

“…However, the development of a complete upper and lower rhamphotheca paralleled by partial or complete edentulism is a derived character that appears within different maniraptoriform lineages (Ornithomimosauria, Oviraptorosauria). Basal taxa of each clade (Perez-Moreno et al, 1994;Balanoff et al, 2009) are characterized by the possession of teeth and a comparatively unspecialized cranial design, with various stages of partial tooth loss in individual taxa (Ji et al, 1998;Kobayashi and Barsbold, 2005b). Dentitions are subject to strong functional pressures and are constantly used for foraging, prey capture, or food manipulation.…”

New tyrannosaur from the mid-Cretaceous of Uzbekistan clarifies evolution of giant body sizes and advanced senses in tyrant dinosaurs

“…In posterior view, the width across the opposing cristae is greater than half the depth of the braincase as in Guanlong, Dilong, and Xiongguanlong, but unlike the narrower cristae in tyrannosaurids (20), other coelurosaurs (23,(31)(32)(33), and outgroups (17,18). The otic recess (= columellar canal) is a deep funnel whose wide external opening trends medially into the braincase interior, where it is divided into a pneumatic opening supplying the posterior tympanic recess and the fenestrae vestibuli and pseudorotunda.…”

“…The pocket is shallow as in basal tyrannosauroids, not deeply concave as in tyrannosaurids (2,20). There is no such pocket in dromaeosaurids and other derived coelurosaurs, in which the nerve foramina are flush with the external surface of the otoccipital (23,(31)(32)(33).…”