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Journal of Paleontology

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AN OSSIFIED TENDON TRELLIS IN CHASMOSAURUS (ORNITHISCHIA: CERATOPSIDAE)

¹ Earth Sciences, Canadian Museum of Nature, PO Box 3443, STN "D", Ottawa, Ontario K1P 6P4, <rholmes@mus-nature.ca>
² Department of Organismic and Evolutionary Biology, 26 Oxford Street, Harvard University, Cambridge, Massachusetts 02138, <corgan@oeb.harvard.edu>

The first 20% of the full text of this article appears below.

	INTRODUCTION

 
THE ORNITHISCHIA and its sister group, the Saurischia, comprise the Dinosauria. Ornithischians (Weishampel, 2004) are a diverse group of primarily quadrupedal herbivores that include such familiar dinosaurs as the armored stegosaurs and ankylosaurs (Thyreophora), as well as the duckbilled hadrosaurs, pachycephalosaurs, and ceratopsians (Cerapoda). The Ceratopsia (You and Dodson, 2004) includes a number of relatively small basal forms such as psittacosaurs and Neoceratopsia, which comprises protoceratopsids and the larger, more derived horned Ceratopsidae.

Ossified tendons occur throughout the body of many birds (Vanden Berge and Storer, 1995), but reports in other Saurischia are rare (but see Sereno et al., 2004). However, they occur in nearly all ornithischian dinosaurs except stegosaurs (Sereno and Dong, 1992). The presence of ossified tendons above the sacrum is thought to be a diagnostic character of the Ornithischia (Weishampel, 2004). Many taxa also develop them in association with the caudal and/or thoracic vertebrae. Ossified tendons usually occur in bundles along the epaxial region of the vertebral column and the hypaxial region of the tail in basal ornithopods such as Hypsilophodon Galton, 1974. Similar tendon bundles are known in pachycephalosaurs (Sues and Galton, 1987) and ankylosaurs possess tendons associated with the tail "club" (Coombs, 1995). The ornithopod group Iguanodontoidea (Hadrosauridae and Iguanodontidae plus Protohadros Head, 1998 and Ouranosaurus Taquet, 1976) developed a rhomboidal trellis of ossified tendons (Fig. 1), often considered to be synapomorphic (e.g., Sereno, 1999), along the dorsal side of their vertebral columns (Dollo, 1886; Brown, 1916; Parks, 1920; Lull and Wright, 1942; Norman, 1980, 1986; Prieto-Márquez, 2001; Horner et al., 2004). Note that Hadrosauriformes is synonymous with Iguanodontoidea, but the latter is preferred (. . . [Full Text of this Article]