Thursday, May 27, 2010

Neuroanatomy (2)


Incisivosaurus gauthieri, Oviraptorid
Dr. Xing Xu, Dr. Yoshimura Kobayashi, Dr. Yusuke Matsufune, and Dr. Mark A. Norell

"The imagery on this page is the basis for a paper entitled Cranial osteology of the theropod dinosaur Incisivosaurus gauthieri (Theropoda: Oviraptorosauria), by A.M. Balanoff, X. Xu, Y. Kobayashi, Y. Matsufune, and M.A. Norell, 2009 (American Museum Novitates 3651:1-35)."
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 a 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.
The simpler explanation is that oviraptors are secondarily flightless members of paraves.

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