Orcemys, a new genus of arvicolid rodent from the early Pleistocene of the Guadix–Baza Basin, southern Spain

Abstract

A new arhizodont arvicoline rodent is described from early Pleistocene deposits of Barranco de los Conejos and Barranco del Paso in the Guadix–Baza Basin of southern Spain. The molars of Orcemys appear to represent a paedomorphic origination from a large rhizodont Mimomys. A few dental characters of Orcemys are superficially similar to those of the lagurines, but the presence of sparse cementum in reentrant folds and a Mimomys-kante formed opposite T5 on the first lower molar clearly identify Orcemys as an arvicoline. The character mosaic of Orcemys is unique among large early Pleistocene voles and the dentition of a potential ancestor probably resembled that of Mimomys medasensis with a tendency towards simplification. With Tibericola vandermeuleni and Mimomys oswaldoreigi, Orcemys represents one of the earliest experiments with arhizodonty among European voles. Including Mimomys medasensis at Barranco del Paso, this set of arvicolids redefines a previously recognized early Pleistocene MmQ1 biozone in Spain.