Reassessment of the North American pelobatid anuran Eopelobates guthriei

Abstract

Eopelobates guthriei Estes, 1970, is based on a partial skull and associated right scapula from the Early Eocene Wind River Formation (Lysitean), Fremont County, Wyoming. Reexamination of the holotype and only known specimen reveals that it should no longer be regarded as Eopelobates because it lacks characters considered to be diagnostic of that genus. Comparison to other pelobatids indicates it is most similar to Scaphiopus and Spea in possession of an elongate postchoanal ramus of the vomer. It compares more closely with Scaphiopus in its lack of hypossification of cranial bones and possession of a long, low, arcuate ventral flange of the pterygoid. There is no evidence to suggest that it represents a new genus, but because it is not known if the postcranial skeleton was specialized for burrowing, as in Scaphiopus and some other pelobatids, it is only tentatively referred to Scaphiopus as cf. S. guthriei (Estes, 1970). Two derived characters distinguish cf. Scaphiopus guthriei from other Scaphiopus: 1) frontoparietal narrowest just posterior of the supraorbital flange and 2) otic ramus of squamosal long and thin. Assuming assignment to Scaphiopus is correct, then the temporal range for Scaphiopus can be extended back from the Middle Oligocene to the Lower Eocene.