A Nimravid (Mammalia: Carnivora) with Split Carinae, Supporting the Hypothesis of Genetic Polymorphism in Homologous Tooth Abnormality Found Within Theropod Dinosaurs

WELSH, Ed; Badlands National Park, Interior, SD. BOYD, Clint A.; North Dakota Geological Survey, Bismarck, ND. SPEARING, Kurt; Morningside College, Sioux City, IA.


The morphological anomaly of split carinae is a tooth abnormality which is well documented in disparate theropod taxa within Tyrannosauridae, Dromaeosauridae, and Carcharodontosauridae. This abnormality is noted in other vertebrate groups (e.g., Chondrichthyes and Phytosauria). Among these groups, only the theropods have been thoroughly examined to determine the cause of the split carinae abnormality. The three most parsimonious hypotheses that have been proposed for this particular abnormality are: it results from trauma; it results from aberrant tooth replacement; or, it is a form of genetic polymorphism. The frequent replacement of teeth in these taxonomic groups have made it difficult to provide a definitive causality for split carinae. We report on an anomalous specimen of the nimravid Dinictis felina, which displays the split carinae abnormality. The anterior carinae in the left and right upper canines of this specimen display normal orientation and serration morphology from the apex until the carinae bifurcate, with the accessory carinae diverging laterally before curving dorsally towards the tooth base. The anterior position of split carinae in Dinictis felina is similar to what has been observed in theropods, suggesting a homologous origin for the abnormality. We propose that genetic polymorphism is the most parsimonious interpretation for the origins of split carinae in both mammals and theropods, due to the nimravid’s constrained tooth replacement, the bilateral symmetry of the split carinae, and lack of evident trauma.