The anatomy and systematic position of the theropod dinosaur Chilantaisaurus tashuikouensis Hu, 1964 from the Early Cretaceous of Alanshan, People's Republic of China

Benson, R. B. J. and Xing, Xu (2008) The anatomy and systematic position of the theropod dinosaur Chilantaisaurus tashuikouensis Hu, 1964 from the Early Cretaceous of Alanshan, People's Republic of China. Geological Magazine, 145 (6). pp. 778-789. DOI 10.1017/S0016756808005475

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Abstract

There is little consensus on the systematic position of the colossal theropod dinosaur Chilantaisaurus tashuikouensis from the Cretaceous (Aptian–?Albian or Upper Cretaceous) Ulansuhai Formation of Inner Mongolia, which has been recovered as a derived member of both Allosauroidea and Spinosauroidea by numerical phylogenetic analyses. Redescription of the type material of C. tashuikouensis reveals an unusual combination of morphological features that render determination of its systematic position problematic. It possesses anatomical features that have been proposed as synapomorphies of Neotetanurae: a preacetabular fossa on the ilium, and a wedge-shaped cross-section of the shaft of the third metatarsal. It also shares some features with specific allosauroid taxa: a pronounced ulnar epicondyle on the humerus, and a prominent medial shelf bounding the preacetabular fossa on the ilium (also present in tyrannosauroids). However, it lacks some features that are present in all other allosauroids: a marked depression on the anterior surface of the distal humerus adjacent to the ulnar condyle, and a humerus that is less than 0.4 times the length of the femur; it furthermore possesses a tibial astragalar facet that is approximately 10% of the tibial length, which suggests a more basal position within Tetanurae. Chilantaisaurus shares certain features with some spinosauroids: an enlarged and elongated first manual ungual, and a suprastragalar buttress that has been modified to a vertical ridge, but these characters are not unique to spinosauroids. A highly reduced fourth trochanter may be an autapomorphy of Chilantaisaurus, as has previously been suggested, or unite the taxon with Coelurosauria in an entirely novel grouping. On the basis of these observations it is likely that Chilantaisaurus is a neotetanuran, but unlikely that it is an allosauroid. Chilantaisaurus may belong to an alternative lineage of very large theropods that continued into the Cretaceous from the diversification of basal neotetanurans during the Middle Jurassic.

Item Type:	Article
Uncontrolled Keywords:	08AREP; IA57;
Subjects:	04 - Palaeobiology
Divisions:	04 - Palaeobiology
Journal or Publication Title:	Geological Magazine
Volume:	145
Page Range:	pp. 778-789
Identification Number:	10.1017/S0016756808005475
Depositing User:	Sarah Humbert
Date Deposited:	01 Apr 2009 12:38
Last Modified:	11 Jul 2014 11:42
URI:	http://eprints.esc.cam.ac.uk/id/eprint/889

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