The Braincase Assigned to the Ornithopod DinosaurUteodonMcDonald, 2011, Reassigned toDryosaurusMarsh, 1894: Implications for Iguanodontian Morphology and Taxonomy

Abstract

ABSTRACT The braincase from the Upper Jurassic (lower Tithonian) Morrison Formation of the Carnegie Quarry at Dinosaur National Monument (Utah), which was assigned to the ankylopollexian iguanodontian ornithopod dinosaur Uteodon aphanoecetes (Carpenter and Wilson, 2008) is actually that of the dryosaurid iguanodontian Dryosaurus cf. D. altus (Marsh, 1878). The purported braincase autapomorphy of U. aphanoecetes, occipital condyle projects farther ventrally than basal tubera, is an artifact of damage to the latter structures in this specimen. The newly identified braincase of Dryosaurus Marsh, 1894, reveals features that are not easily observed in other specimens of this taxon, such as well-developed fossae on the anterior surfaces of the paroccipital processes and a spike-shaped parasphenoid that lacks the dorsal process seen in Dysalotosaurus Virchow, 1919. The distinction of this latter dryosaurid genus from Dryosaurus is here regarded as tentative. The removal of the braincase in question from the hypo...