Table of Content

15 June 2012, Volume 50 Issue 2

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NEW INFORMATION ON THE BRAINCASE OF SINRAPTORDONGI (THEROPODA: ALLOSAUROIDEA): ETHMOIDAL REGION, ENDOCRANIAL ANATOMY, AND PNEUMATICITY

Ariana PAULINA CARABAJAL, Philip J. CURRIE

2012, 50(2):  85-101. 

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 Sinraptor dongi is a large theropod from the upper Shishugou Formation (Jurassic) of Xinjiang in northwestern China. The holotype includes a well-preserved braincase that recently benefited from additional preparation. The ossified ethmoidal elements are U-shaped in cross-section. When placed in anatomical position in the braincase, an unossified space remains between the sphenethmoid and the orbitosphenoid, suggesting there was a cartilaginous septosphenoid when the animal was alive. The morphology of the endocranial cavity and pneumatic recesses was studied using a latex endocast and CT scans. This led to the recognition of some traits that have not been previously described. The presence of a well developed caudal tympanic recess (generally considered as characteristic of coelurosaurs) is particularly interesting, as is the internal morphology of the basisphenoidal recess and its associated pneumatic cavities. There is a longitudinal passage connecting the lateral tympanic recess with the basisphenoidal recess that probably had both pneumatic and vascular functions. Endocranially, there is no medullar eminence, and the opening for the floccular recess is hourglass-shaped. The volume of the endocranial cavity, excluding the olfactory tract and bulbs, is 95 ml, and the encephalization quotient falls within the range calculated for other basal tetanurans. The angles formed between forebrain, midbrain and hindbrain are similar to those in carcharodontosaurids (Carcharodontosaurus and Giganotosaurus), although the relative positions of cranial nerves II-IV varies amongst these taxa. Cranial nerves IX, X and XI pass through a single half-moon-shaped opening. Within Allosauroidea, the cranial endocast of Sinraptor is morphologically more similar to those of Allosaurus, Carcharodontosaurus and Giganotosaurus than to that of Acrocanthosaurus.

A TYRANNOSAUROID FRONTAL FROM THE UPPER CRETACEOUS (CENOMANIAN-SANTONIAN) OF THE GOBI DESERT, MONGOLIA

Takanobu TSUIHIJI, Mahito WATABE, Khishigjav TSOGTBAATAR, Rinchen BARSBOLD,Shigeru SUZUKI

2012, 50(2):  102-110. 

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 An isolated frontal found at the Tsagaan Teg locality in the Gobi Desert is described. Such features as a short orbital rim and the presence of a sagittal crest indicate that this specimen belongs to Tyrannosauroidea. Because the sediment cropping out at Tsagaan Teg is considered as belonging to the Cenomanian-Santonian Bayn Shire Formation, the present specimen contributes to improving the extremely poor fossil record of tyrannosauroid theropods in the lower Upper Cretaceous. 

YIXIANOSAURUS LONGIMANUS(THEROPODA: DINOSAURIA) AND ITS BEARING ON THE EVOLUTION OF MANIRAPTORA AND ECOLOGY OF THE聽JEHOL聽FAUNA

Jehol Biota, Dinosauria, Maniraptora, phalangeal index, paleoecology, allometry

2012, 50(2):  111-139. 

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聽We re-examine the partial skeleton of the enigmatic small feathered theropodYixianosaurus聽longimanus聽from the Lower Yixian Formation, China. A phylogenetic analysis recovers聽Yixianosaurus聽as a basal maniraptoran, in a polytomy withAlvarezsaurus, Therizinosauria, Alvarezsauroidea excluding聽Alvarezsaurus, and a well-resolved clade of derived maniraptorans including Oviraptorosauria and Paraves. The blend in聽Yixianosaurus聽of primitive traits, such as a low brachial index and robust digit III, and derived traits such as a subrectangular coracoid,聽suggests a more complicated mosaic of forelimb evolution within Maniraptora than previously proposed. The robust forelimb bones and massive, recurved, and pointed manual unguals suggest聽Yixianosauruswas predatory, although this assessment remains tentative until more complete fossils of this taxon are found. The basal maniraptoran phylogenetic position implies a larger range of forelimb morphologies at this point in coelurosaurian evolution. In many ways, the robust forelimb and hypertrophied recurved unguals are similar to those of聽Tanycolagreusand聽Coelurus,聽and may be morphologically transitional between these taxa and basal therizinosaurs and oviraptorosaurs. The presence of large, veined, pennaceous contour feathers on聽Yixianosaurus聽indicates the origin of these integumentary structures may be deeper in coelurosaur phylogeny than previously reported. Finally, the robust, elongate forelimbs suggest a different ecological role than inferred for other sympatric small theropods, and lend support to the idea of niche partitioning among the small non-avian theropods of the Jehol聽fauna.聽

THE TAXONOMY OF THE TROODONTID IVPP V 10597 RECONSIDERED

XU Xing, ZHAO Qi, Corwin Sullivan, TAN Qing-Wei, Martin SANDER, MA Qing-Yu

2012, 50(2):  140-150. 

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 The partial troodontid hindlimb IVPP V 10597 was originally described as a juvenile Saurornithoides mongoliensis. The present study reconsiders the taxonomic placement of this interesting specimen, given the significant advances in understanding of the Troodontidae that have taken place since it was first described. Morphological comparisons and numerical phylogenetic analyses indicate that V 10597 is more closely related to the sympatric Linhevenator tani than to Saurornithoides mongoliensis, raising the possibility that V 10597 might be a juvenile L. tani. However, V 10597 differs significantly from other troodontids, including L. tani, in numerous hindlimb features and particularly in the proportions of various hindlimb elements. These differences are likely to be taxonomic, and suggest that V 10597 represents a new troodontid. Furthermore, histological analysis indicates that V 10597 is unlikely to be a juvenile ofL. tani or any other large troodontid. Based on the available morphological and histological information, we propose the erection of a new taxon, Philovenator currieigen. et sp. nov., based on V 10597. This new find increases the known taxonomic diversity and morphological disparity of Late Cretaceous troodontids. 

THE ENIGMATIC REPTILE PACHYSUCHUS IMPERFECTUS YOUNG, 1951 FROM THE LOWER LUFENG FORMATION (LOWER JURASSIC) OF YUNNAN, CHINA

Paul M. BARRETT, XU Xing

2012, 50(2):  151-159. 

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 Phytosaurs are generally considered to have become extinct at the end of the Triassic Period, but several records have suggested that they survived into the basal Jurassic in Europe and Asia. The Asian record consists of Pachysuchusimperfectus from the Lower Lufeng Formation (?Hettangian–Sinemurian) of Yunnan, China. However, this specimen differs from phytosaurs in numerous respects and is more likely a poorly preserved, indeterminate sauropodomorph dinosaur skull. The referred specimens of this species are also regarded as indeterminate, thereby removing the post-Triassic record of phytosaurs from Asia. The European records of Jurassic phytosaurs are also shown to be doubtful, suggesting that this clade was restricted to the Late Triassic.

RE-EVALUATION AND PHYLOGENETIC ANALYSIS OF WULAGASAURUS DONGI, A HADROSAURINE DINOSAUR FROM THE MAASTRICHTIAN OF NORTHEAST CHINA

XING Hai, Albert PRIETO-MáRQUEZ, GU Wei, YU Ting-Xiang

2012, 50(2):  160-169. 

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The diagnosis of the hadrosaurine Wulagasaurus dongi is revised in this paper, based on both original and new material recovered from the Upper Cretaceous Yuliangzi Formation at the Wulaga locality in Heilongjiang Province,China. However, we also demonstrate that some specimens previously referred to W. dongi, including braincases, maxillae and scapulae, actually belong to typical lambeosaurines.Wulagasaurus shares strong morphological similarities with the North American taxa Brachylophosaurus and Maiasaura: a long, wedge-shaped rostral apex positioned at the level of the dorsoventral midpoint of the jugal rostral ramus; a fan-shaped caudal ramus of the jugal with a nearly straight or slightly convex caudal margin; a relatively elongate and slender ventral process of the coracoid; a weakly developed humeral deltopectoral crest that is moderately expanded craniolaterally; and an asymmetrical, strongly convex margin of the iliac supracetabular process, lacking a strong ridge connecting its caudal portion with the dorsal margin of the postacetabular process. Phylogenetic analysis indicates that Wulagasaurus,Brachylophosaurus and Maiasaura form a monophyletic basal clade of hadrosaurines. This basal clade originated in Asiaduring the Santonian age of the Late Cretaceous. No later than the middle Campanian, the lineage split and then dispersed via the Bering land bridge to North America, whereBrachylophosaurus and Maiasaura diverged from one another.

AURORACERATOPS SP. (DINOSAURIA: NEOCERATOPSIA) FROM THE EARLY CRETACEOUS OF THE MAZONGSHAN AREA IN NORTHWESTERN CHINA

YOU Hai-Lu, Eric MORSCHHAUSER, Peter DODSON, LI Da-Qing

2012, 50(2):  170-180. 

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A specifically indeterminate specimen of the basal neoceratopsian dinosaur Auroraceratops is described. Auroraceratops sp.is based on a partial articulated skeleton, including the skull and lower jaw, collected from the Lower Cretaceous Xinminpu Group in the Yujingzi Basin of the Mazongshan area, northwestern China. A. sp.differs from the type species A. rugosus in having a longer face and a narrower nasal, among other features. The finding of A. sp. extends the geographic distribution of this genus approximately 100 km southeast, and makes the Early Cretaceous Mazongshan area the richest single basal neoceratopsian locality in the world.