Article: The skull of the herbivorous synapsid Edaphosaurus boanerges from the Lower Permian of Texas

The cranial anatomy of the Lower Permian synapsid Edaphosaurus boanerges is described, based upon well-preserved material from the Geraldine Bonebed (Wichita Group: Nocona Formation) of north-central Texas. Two autapomorphies for this species are identified: (1) 120-150 teeth are present on each palatal tooth plate; and (2) the mandibular symphysis is deeply excavated dorsally. Phylogenetic analysis of the interrelationships of Edaphosaurus species supports the hypotheses that the Lower Permian Texan species E. boanerges, E. cruciger, and E. pogonias are a monophyletic group, and E. boanerges is excluded from a clade formed by E. cruciger and E. pogonias. The suite of cranial specializations that characterizes Edaphosaurus is interpreted as an adaptation complex towards terrestrial herbivory. Isodonty, the presence of cutting edges on the marginal teeth, the oblique orientation of the cutting edges, and the shouldering of the marginal teeth, indicate that the anterior marginal teeth of E. boanerges served to crop bite-sized portions from tough, terrestrial plants. The food was then triturated by the palatal and mandibular tooth plates; minor grinding was provided also by the procumbent posterior teeth of the maxilla and dentary. The morphology of the jaw suspension indicates that the mandible was capable of fore-and-aft translation; the orientation of tooth plate occlusal surfaces and palatal tooth wear in E. boanerges indicate that propalinal movement was a major component of the grinding phase during oral food processing. The dual organization of the feeding system in Edaphosaurus is the earliest known example of its kind among amniotes.