Abstract

Two incomplete teeth of the chondrichthyan genus Edestus are reported. They were collected from the Gray Mesa Formation (Pennsylvanian, late Desmoinesian), Socorro County, New Mexico, in 1996. The better-preserved tooth belongs to Edestus sp. cf. E. heinrichi. The other cannot be identified beyond the generic level. These are the first specimens of the genus known to be reported from New Mexico. The only other specimens known from the Rocky Mountain region are from Colorado. Both the New Mexico and Colorado collections are from marine limestones. In North America, Edestus is most common in marine black shales of the Illinois Basin, but to date has not been found in marine gray shales or limestones in the Appalachian Basin. The failure to find Edestus remains in the Appalachian Basin is probably the result of the precise timing and limited extent of marine incursions into that region. Edestus might have been less tolerant of restricted marine environments than other chondrichthyans collected from Pennsylvanian deposits in the Appalachian Basin. The function of the symphyseal tooth whorls of Edestus is obscure, inasmuch as their convex curvature makes them poorly-adapted to the “scissors” function proposed in some previous studies. Alternatively, it is proposed here that Edestus teeth were used to disable prey with a slicing action carried out with a vertical motion of the head, with jaws fixed relative to each other, and not with a scissors-like action of the jaws moving relative to each other. This hypothesis is supported by the author’s observations of wear and damage on the teeth of the holotype of Edestus newtoni. Helicoprion tooth whorls are similar to those of Edestus in that they contain sharp, serrated tooth crowns along the convex margin of the whorls and extend outside the oral cavity. The whorls might have functioned similarly to the manner that is hypothesized for Edestus, that is, to slash prey with a downward motion of the head, with jaws fixed. This proposed similarity in form and function would likely represent convergence.