APPENDICULAR OSTEOLOGY OF DREADNOUGHTUS SCHRANI, A GIANT TITANOSAURIAN (SAUROPODA, TITANOSAURIA) FROM THE UPPER CRETACEOUS OF PATAGONIA, ARGENTINA

摘要

The postcranial anatomy of giant titanosaurians remains poorly known because of a combination of preservational and collection biases. Dreadnoughtus schrani, a recently described, large titanosaur from the CampanianMaastrichtian Cerro Fortaleza Formation of Santa Cruz Province, Argentina, offers the first opportunity for detailed study of appendicular anatomy of a truly giant titanosaurian. The entire appendicular skeleton is represented except the manus and portions of the pes. Comparisons with related titanosauriforms reveal that the holotype skeleton (MPM-PV 1156) exhibits three appendicular autapomorphies: (1) a cranioventrally-caudodorsally oriented ridge across the medial surface of the cranial end of the scapular blade; (2) a distinct concavity on the caudomedial surface of the proximal radius; and (3) the distal end of the radius is subrectangular with subequal craniocaudal and mediolateral dimensions. Appendicular synapomorphies shared between Dreadnoughtus and other titanosauriforms encompass a wide range of body sizes, from the giant Argentinosaurus to the dwarf Magyarosaurus. Among described titanosauriforms, only a single feature occurs exclusively among the appendicular skeletons of the largest taxa: an accessory ventrolateral process is present on the preacetabular lobe of the ilium in Dreadnoughtus, Alamosaurus, and Giraffatitan. This process appears to have arisen in response to greater stress applied by hind limb adductor musculature in these giant terrestrial vertebrates. Continued investigation of titanosaurian anatomy, myology, and biomechanics is needed to gain greater understanding of the functional nature of widegauge posture.