REDESCRIPTION OF A LARGE PALEOCENE GAVIALOID FROM THE EAST COAST OF NORTH AMERICA

The East Coast of the United States preserves a rich history of Paleocene crocodylians. Much debate has been given to the taxonomic affinity of the late Paleocene crocodylian “Crocodylus clavriostris”, which has been attributed to both Thoracosaurus neocesariensis and Eosuchus minor. However, C. clavirostris was significantly larger than T. neocesariensis and E. minor. Our phylogenetic analysis places C. clavirostris as a gavialoid, basal to the Eosuchus clade. The species can be differentiated from T. neocesariensis and E. minor based on the morphology of the external naris, choanal septum, lack of an enlarged foramen aereum on the quadrate, frontal morphology, and palatine morphology. In addition to the holotype material, five additional skulls and four lower jaws have also been assigned to this taxon from the Aquia and Vincentown formations. For the first time a complete rostrum of C. clavirostris has been discovered, which reveals an enlarged bowl-shaped external naris that nearly encompasses the entire anterior portion of the rostrum. A regression analysis on a composite skull of C. clavirostris reveals that the estimated total body length for the animal was 8-8.5 meters, making it one of the largest North American Cenozoic crocodylians. This species is also known for its peculiar antorbital fenestra, which separates the lacrimals from the prefrontal. However, upon further investigation on three skulls with this purported feature, it is clear that these openings represent breaks in the cortical bone, rather than a distinct anatomical feature. None of the fenestra were symmetric in position or consisting of finished bone their borders, and are likely a preservational or preparational artifact.