Morphometric evolution of Mimomys savini (Rodentia, Mammalia): A new view of its morphological changes

Abstract

Mimomys savini is a very important arvicoline as it represents a useful biochronological tool in the study of the first human arrivals in Europe and its expansion across the continent. To date, evolution studies on this species have focused on its size changes and the loss of ancestral characteristics.This work sheds further light on the evolution of this taxon, through a study of the morphological changes in its first lower molar, using, for the first time, 2-D geometric morphometrics techniques based on landmark configurations. To do this, we have analyzed M. savini remains spanning 1.4 to 0.78 Ma from the Gran Dolina site (Sierra de Atapuerca, Spain), Barranco León site (Orce, Spain), and Barranc de la Boella site (Tarragona, Spain).Our results show a set of occlusal surface shape differences between the more recent and older populations. The oldest populations are characterized by a more developed lingual re-entrant angle 4 (LRA4); a less developed buccal re-entrant angle 3 (BRA3); a narrower lingual re-entrant angle 1 (LRA1); and a wider neck of the head of the anteroconid complex (ACC) than in more recent populations. Moreover, despite the increase in m1 length and width during the evolution of M. savini, it seems that the size of the occlusal surface decreased (maybe as a consequence of shape changes, such as neck width or the size of re-entrant angles).Finally, the shape and size comparisons of the populations studied reinforces previously proposed chronologies for Barranc de la Boella, and suggests a site age similar to that of Gran Dolina (section TD6 -TD5).