Fourier analysis applied to Cricetodon and Hispanomys (Rodentia, Mammalia): its use as a taxonomical criterion

Cricetodon and Hispanomys are two extinct rodent genera belonging to the same tribe. Cricetodon presents generally a more primitive morphology than Hispanomys. However, they share some traits and some species present a combination of primitive and derived characters (called mosaic morphological pattern) that difficult assessing the evolutionary stage of the species or their attribution into a genus. Fourier Shape Analysis, a geometric morphometrics method, is used to quantify the outline form of the upper first molar of these genera and to differentiate them. New mathematical criterion is obtained to analyse the morphology of this particular species with mosaic morphology. First, the validity of the method is tested with one basal (C. meini) and one derived species (H. aragonensis). Two different outlines are statistically distinguished: straight in Cricetodon and trilobed in Hispanomys. This result allowed us to undertake the study of some other species included in both genera. This complete analysis enabled us to describe the outline of ‘Cricetodon’ klariankae and ‘Cricetodon’ fandli. Both share the same morphospace than the rest of the species of Hispanomys. This could indicate that both species could be included in Hispanomys.