The imagery on this page is supporting material for a paper entitled A review of the Mongolian Cretaceous dinosaur Saurornithoides (Troodontidae: Theropoda), by M.A. Norell, P.J. Makovicky, G.S. Bever, A.M. Balanoff, J.M. Clark, R. Barsbold, and T. Rowe, 2009 (American Museum Novitates 3654:1-63). The abstract is as follows:

       We review the morphology, taxonomy, and phylogenetic relationships of the upper Cretaceous        Mongolian troodontid Saurornithoides. Saurornithoides mongoliensis is known only by the holotype        from Bayan Zag, Djadokhta Formation. This specimen includes a nearly complete, but weathered, skull        and mandibles, a series of dorsal, sacral, and caudal vertebrae, and a partial pelvic girdle and hind        limb. Saurornithoides junior, here referred to Zanabazar, also is known only by the holotype from        Bugiin Tsav, Nemegt Formation. This specimen consists of a skull and partial mandible, a series of        sacral and caudal vertebrae, a partial pelvic girdle, and the distal part of the right hind limb.        Saurornithoides + Zanabazar is one of the few Mongolian taxa known from both the Djadokhta and        Nemegt formations. The monophyly of Saurornithoides + Zanabazar has not been seriously questioned        historically, yet empirical support for this clade is currently tenuous. A privileged phylogenetic        relationship between Saurornithoides, Zanabazar, and the North American troodontid Troodon        formosus is supported by numerous characters including the presence of a subotic recess,        lateroventrally projecting and hollow basipterygoid processes, a lacrimal whose anterior process is        significantly longer than its posterior process, a highly pneumatized parasphenoid rostrum, a        constricted neck of the occipital condyle, a symphyseal region of the dentary that is slightly        recurved medially, and an obturator process located near the middle of the ischiadic shaft. CT data        for the skulls of both species facilitated a description of the endocranial anatomy of Saurornithoides        mongoliensis and Zanabazar junior, including a reconstruction of the endocranial space of Zanabazar        junior (see Additional Imagery). Despite being the largest of the known troodontid species, the        endocranial volume of Zanabazar junior is considerably smaller than that estimated for Troodon        formosus, suggesting that the extremely high encephalization quotient of Troodon formosus may be        autapomorphic among troodontids.

This specimen, the holotype and only known specimen of this species, was collected from the Upper Cretaceous locality of Bugiin Tsav by the first joint Mongolian-Soviet Paleontological Expedition. It was made available to the University of Texas High-Resolution X-ray CT Facility for scanning by Dr. Mark Norell of the American Museum of Natural History.

This specimen was scanned by Richard Ketcham and Matthew Colbert on 31 October 2000 along the coronal axis for a total of 625 slices. Each 512 x 512 pixel slice is 0.5 mm thick, with an interslice spacing of 0.45 mm (for a slice overlap of 0.05 mm) and a field of reconstruction of 117 mm.

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Click on the thumbnail to the left for a roll animation (1.4 mb) of the Zanabazar cranial endocast highlighted in green within the skull, which is rendered semi-transparent.

Click on the thumbnail to the left for a roll animation (2.5 mb) of the isolated Zanabazar cranial endocast.

Click on the thumbnail to the left for a yaw animation (1.2 mb) of the Zanabazar cranial endocast highlighted in green within the skull, which is rendered semi-transparent.

Click on the thumbnail to the left for a yaw animation (2.6 mb) of the isolated Zanabazar cranial endocast.

Click on the thumbnail to the left for a pitch animation (1.1 mb) of the Zanabazar cranial endocast highlighted in green within the skull, which is rendered semi-transparent.

Click on the thumbnail to the left for a pitch animation (2.1 mb) of the isolated Zanabazar cranial endocast.