Morphometric variability in the first lower molars of North American Ogmodontomys (Arvicolidae, Rodentia, Mammalia) determined by Fourier analysis

The Meade Basin of southwestern Kansas (USA) has long been known for its representation of late Neogene and Quaternary mammalian faunas. The genus Ogmodontomys (Arvicolidae, Rodentia) first appeared during the Early Blancan and ranges through much of the Pliocene on the Great Plains. A decomposition of the first lower molar occlusal and linea sinuosa contours by means of Fourier Analysis was performed on six stratigraphically superposed samples of Ogmodontomys first lower molars (m1s) from the Meade Basin, spanning an interval of approximately 1.8 million years of the Early and Middle Pliocene. The results consistently grouped samples in stratigraphic order, and suggest the presence of two species of Ogmodontomys, one beneath the Bishop Gravel (O. sawrockensis) and another from the top of and above the gravel (O. poaphagus). The method is also useful to place samples of uncertain stratigraphic position in the Meade Basin chronological sequence as long as Ogmodontomys m1s are present.