TOOTH MARK ANALYSIS OF DIMETRODON APPENDICULAR SKELETAL ELEMENTS WITH IMPLICATIONS OF FEEDING STRATEGIES

The Late Paleozoic pelycosaurs signify an important step in the evolution of synapsid reptiles to mammals. The Craddock Ranch bonebed in Seymour, Texas is well known for the prevalence of the pelycosaur fossils including the apex predator, Dimetrodon. Dimetrodon skeletal elements recovered have been noted to posses substantial tooth marks, which indicate that cannibalism was prevalent. To date, these tooth marks have not been utilized for determining detailed feeding priorities and methodologies. This study tests if tooth marks placement and morphology indicate priority muscles targets for Dimetrodon feeding. Furthermore, this research utilizes the data gathered from the Dimetrodon skeletal elements to make a comparison with prehistoric (Mesozoic therapods) and modern taxa (Varanus komodoensis). The skeletal elements utilized for this analysis include the scapular blade, clavicle, coracoid, interclavicle, pelvis, and femur.

The scapular blades exhibited a large amount of tooth marks across the dorsal edge with additional feeding along the ventral edge to a lesser extent. The tooth marks observed on the clavicles were consistently observed along the edges of the expanded lower portion. The coracoids had tooth marks located in proximity to the posterior edges. The tooth marks noted on the interclavicles were primarily located along the thin edges where muscle attachments were focused. The pelvis was a major target of feeding with the illium most frequently marked followed by the ischium and pubis. The most frequent muscle targets were along the dorsal edges of the illium. In the case of the ischium and pubis, tooth marks were most frequent along the ventral edges. In the case of the femur, the bite marks indicate that common feeding targets were the femoral attachments of muscles that originated from the pelvis. The bite marks analyzed on the Dimetrodon skeletal elements compared favorably to those noted on the bones of V. komodoensis prey. Both sample groups indicate the shoulder girdle and pelvis were the high priority feeding targets, an absence of gnawing or bone fracturing behavior during feeding, and a propensity to form tooth mark parallel clusters. However, the Dimetrodon bite marks were primarily edge marks that lacked curvature whilst V. komodoensis bite marks exhibited curvature and were identified as scores.