Taxonomy of the Pleistocene giant beaver Castoroides (Rodentia: Castoridae) from the southeastern United States

Abstract

Two late Pleistocene skulls of Castoroides from Florida share a suite of morphologic features with two partial skulls from the early Pleistocene of Florida (including the holotype of Castoroides leiseyorum Morgan and White, 1995) and a late Pleistocene skull from South Carolina. These specimens are regarded as conspecific and can be readily distinguished from skulls of Castoroides ohioensis Foster, 1838 from the northeastern and midwestern United States by a number of characters including absence of a mesopterygoid fossa, shorter sagittal crest, lambdoidal crest strongly inflected anteriorly at midline of skull, larger postorbital process and incisive foramen, cheektooth rows less divergent posteriorly and located more anteriorly (relative to maxillary process of zygomatic arch), and a more massive premaxilla without an anterior protuberance. All Florida samples of Castoroides are now regarded as belonging to a single species that is not Castoroides ohioensis. The rule of nomenclatural priority requires raising Castoroides ohioensis dilophidus Martin, 1969 to the rank of species, Castoroides dilophidus, and regarding it as the senior synonym of Castoroides leiseyorum Morgan and White, 1995. The dental character which formed the basis for the subspecies name dilophidus is only known to occur in some late Pleistocene teeth from peninsular Florida and coastal Georgia, and is not present in all populations of the species C. dilophidus.