DREADNOUGHTUS SCHRANI, AN EXCEPTIONALLY COMPLETE TITANOSAURIAN SAUROPOD DINOSAUR FROM THE UPPER CRETACEOUS OF SOUTHERN PATAGONIA, ARGENTINA

Titanosaurian sauropod dinosaurs were the most diverse and abundant large-bodied herbivores in the southern continents during the Late Cretaceous and are regarded as the most massive land animals yet discovered. Nevertheless, all previously described truly gigantic titanosaurs (body mass > 40 metric tons) are represented by very fragmentary fossils. Our newly described taxon Dreadnoughtus schrani, from Upper Cretaceous sediments in southern Patagonia, Argentina, possesses approximately 60% of the postcranial skeleton.

Bones of Dreadnoughtus schrani (MPM-PV 1156 and 3546) are exquisitely preserved, with details such as muscle scars and other osteological correlates of soft-tissues clearly discernible. Applying a formula for calculating body mass in quadrupedal tetrapods from humeral and femoral midshaft circumferences yields an estimate of 59.3 metric tons for the D. schrani holotype. Reconstruction of the Dreadnoughtus skeleton produces an approximate body length of 26 meters. Skeletal completeness metrics indicate that the new taxon preserves approximately 45.3% of the bones expected in a complete titanosaurian skeleton, and up to 70.4% of the postcranial elements. By comparison, these values are 15.2% and 26.8% for Futalognkosaurus, 7.8% and 12.7% for Paralititan, 5.1% and 9.2% for Argentinosaurus, 2.3% and 3.5% for ‘Antarctosaurus’ giganteus, and 1.6% and 2.8% for Puertasaurus. The new taxon can be definitively evaluated for 57.5% of the morphological characters included in a recently published data matrix. By comparison, Futalognkosaurus and Argentinosaurus can be scored for 18.5% and 12.6% of the available characters, respectively. Dreadnoughtus schrani therefore represents the most complete giant titanosaur yet discovered and offers important new osteological data for future investigations of the anatomy, biomechanics, and evolution of the most massive land animals that have ever existed.