First observed cranial pathology in the early Permian synapsid <i>Dimetrodon limbatus</i>

Dimetrodon is an early non-mammalian synapsid from the early Permian of Europe and North America best known for its elongated neural spines, which in life formed an interconnected sail, and an early occurrence of heterodonty in the fossil record. Previous literature has identified multiple pathologies in the genus, including fractured and healed neural spines and fractured and calloused limb bone midshafts, but no cranial pathologies have been described. We describe the first occurrence of cranial pathology in the genus in a specimen of Dimetrodon limbatus (AMNH FARB 4081) and hypothesize its causation. The pathology is a lesion on the anterior lateral surface of the right dentary directly ventral to the largest caniniform tooth that exhibits a filigree texture and margins of raised cortical surface anteriorly, posteriorly, and ventrally. The absence of a dorsal margin, other abscesses or puncture marks on the specimen characteristic of inter- or intraspecific combat, and the lesion’s location directly ventral to the upper caniniform tooth suggest that the lesion is the result of an accidental self-caused injury, perhaps during prey processing or hunting, in which the upper caniniform punctured the dentary.