Taxonomic Status of the Silver Rice Rat, Oryzomys argentatus

Abstract

A recent revision of Oryzomys of the United States did not include O. argentatus as a valid species possibly because of inadequate samples and omission of three of four skull characters that distinguish the species. A sample of 13 male O. argentatus was compared with 73 male O. palustris and 10 male O. couesi. O. couesi was used as a relative measure of differentiation at the species level. Skull morphology of siblings and laboratory-reared individuals was not significantly different from that of wild individuals. Principal-components analysis of the four skull characters for all skulls showed O. argentatus clustered closely. Canonical discriminant analyses on the four skull characters showed one distinct cluster of O. argentatus and a second containing all O. palustris and O. couesi individuals. On the basis of pelage and osteology, O. argentatus is absolutely distinct from O. palustris and O. couesi. Differences are greater between O. argentatus and O. palustris than between subspecies of O. palustris, and greater between O. argentatus and O. couesi than between O. palustris and O. couesi. Analyses considering the diagnostic skull characters and pelage characteristics support retention of species status for O. argentatus.