VERTEBRAL ANATOMY OF CRYOLOPHOSAURUS ELLIOTI, A THEROPOD DINOSAUR FROM THE EARLY JURASSIC OF ANTARCTICA

Fossil localities discovered in Antarctica in the early 1990’s and early 2000’s have produced a nearly complete theropod dinosaur, the fragmentary remains of a basal sauropodomorph dinosaur, a dimorphodontid pterosaur humerus and a Bienotheroides clade tritylodont tooth. Cryolophosaurus ellioti Hammer and Hickerson, 1994, was discovered in the Early Jurassic Hanson Formation on Mt. Kirkpatrick in the Beardmore Glacier region of the Central Transantarctic Mountains at an altitude of approximately 4100 meters. Cryolophosaurus is the most complete dinosaur yet discovered in Antarctica and represents a theropod from an early critical period in dinosaur evolution. Due to a very limited number of fossils from this period we do not have a clear understanding of the phylogeny of these early theropods. Cryolophosaurus is distinguished from all other theropods by its possession of a distinct cranial crest and, at an estimated body length of 6.5 meters and a weight of 465 kilograms, Cryolophosaurus is the largest theropod known from the Early Jurassic. Earlier studies indicate that Cryolophosaurus is related to a clade of medium-bodied Early Jurassic theropods including ‘Dilophosaurus’ sinensis, Dracovenator regenti and Dilophosaurus wetherilli. This clade challenges the previous understanding of the Coelophysoidea and Ceratosauria, rendering both non-monophyletic. A morphological description of the vertebral column of Cryolophosaurus is presented here that includes many recently prepared new specimens collected in 2003 that were not included in the earlier analyses. The analysis includes five cervical, six dorsal, two sacral and eleven caudal vertebrae. The post-cranial skeleton of Cryolophosaurus preserves a number of morphological characteristics that are useful in interpreting its relationships and position within the phylogeny of theropods.