On the dentition of Meridiania convexa Case (Myliobatoidea), an extinct Early Eocene ray from the United States

A highly fossiliferous Ypresian (lower Eocene) deposit located in Berkeley County, South Carolina, yielded a very diverse elasmobranch assemblage that includes Meridiania convexa Case, 1994. More than 1,800 complete and partial teeth have been recovered, and this sample allows for a more complete understanding of tooth morphology and organization of the dentition. The dentition of Meridiania consisted of a closely packed (but not rigid) arrangement of teeth, with a single row of very wide medial teeth and multiple rows of progressively more symmetrical lateral teeth. Tooth bases are polyaulocorhizous in medial and mesially located lateral teeth, but those of distal lateral teeth are most often holaulocorhizous. Previous assignment of Meridiania to Dasyatidae is rejected in favor of Myliobatidae. Ontogenetic heterodonty is indicated by a change in crown morphology with increased tooth size, with small teeth (juveniles) having a distinct transverse ridge, and large teeth (adults) having more uniformly convex crowns. Extreme wear through in vivo usage suggests that teeth were retained for a long period of time, and the diet of Meridiania consisted of hard-shelled invertebrates. All known occurrences of Meridiania are from coastal plain strata of Ypresian age, and the paleogeographic distribution extends from eastern Texas into northeastern Virginia, USA.