The imagery on this page was the basis for a paper entitled Variation, Variability, and the Origin of the Avian Endocranium: Insights from the Anatomy of Alioramus altai (Theropoda: Tyrannosauroidea) by G.S. Bever, S.L. Brusatte, A.M. Balanoff and M.A. Norell (PLoS One 6(8):e23393. doi:10.1371/journal.pone.0023393, 2011). The abstract is as follows:
The internal braincase anatomy of the holotype of Alioramus altai, a relatively small-bodied tyrannosauroid from the Late Cretaceous of Mongolia, was studied using high-resolution computed tomography. A number of derived characters strengthen the diagnosis of this taxon as both a tyrannosauroid and a unique, new species (e.g., endocranial position of the gasserian ganglion, internal ramification of the facial nerve). Also present are features intermediate between the basal theropod and avialan conditions that optimize as the ancestral condition for Coelurosauria—a diverse group of derived theropods that includes modern birds. The expression of several primitive theropod features as derived character states within Tyrannosauroidea establishes previously unrecognized evolutionary complexity and morphological plasticity at the base of Coelurosauria. It also demonstrates the critical role heterochrony may have played in driving patterns of endocranial variability within the group and potentially reveals stages in the evolution of neuroanatomical development that could not be inferred based solely on developmental observations of the major archosaurian crown clades. We discuss the integration of paleontology with variability studies, especially as applied to the nature of morphological transformations along the phylogenetically long branches that tend to separate the crown clades of major vertebrate groups.
About the Species
This specimen, the holotype, was collected at Tsaagan Khushuu, Nemegt Formation (Maastrichtian) during the Mongolian Academy of Sciences-American Museum of Natural History 2001 expedition. It was made available to the University of Texas High-Resolution X-ray CT Facility for scanning by Dr. Gabe Bever of the New York College of Osteopathic Medicine.
About this Specimen
This specimen was scanned by Matthew Colbert on 21 January 2009 along the sagittal axis for a total of 431 slices. Each 1024 x 1024 pixel slice is 0.25 mm thick with an interslice spacing 0.25 mm and a field of reconstruction = 301.6 mm.
Click on the thumbnail to the left for a yaw animation (2.6 mb) of the isolated Alioramus cranial endocast.
Click on the thumbnail to the left for a pitch animation (2.0 mb) of the isolated Alioramus cranial endocast.
Click on the thumbnail to the left for a yaw animation (11.6 mb) of the Alioramus cranial endocast and sinus cavernosus within the braincase, which is rendered semi-transparent.
Click on the thumbnail to the left for a yaw animation (12.7 mb) of the isolated Alioramus cranial endocast rendered within the disappearing braincase.