First detailed description of Hispanomys bijugatus Mein and Freudenthal, 1971 (Rodentia, Cricetodontinae) from the Upper Aragonian of La Grive-Saint Alban (France): Biostratigraphical implications

The material of Hispanomys bijugatus (Rodentia, Cricetodontinae) from La Grive-Saint Alban (carrière Lechartier, fissure L3) is described for the first time and compared with all species of the genus known to date. As common in the Upper Aragonian populations of Hispanomys, this taxon evidences a low variability. H. bijugatus shows some progressive characters with respect to the remaining Aragonian congeneric species, such as the absence of labial and lingual cingula surrounding the upper and lower molar valleys respectively, the increase in the number of roots on the second lower molar, and the lost of mesolophs. This suggests that H. bijugatus, in spite of being one of the oldest species of the genus, is relatively derived with regard to the coeval congeneric species. Because H. bijugatus and H. decedens are believed to be closely related species within the same lineage, the fact that the former shows a more progressive dental morphology than the latter suggests that the unnamed fissure-fillings from La Grive and La Grive M (with H. decedens only) are older than La Grive L3 (with H. bijugatus only). The coexistence of both species at locality L5 suggests an intermediate age.