Morphological evolution of the murine rodent Paraethomys in response to climatic variations (Mio-Pleistocene of North Africa)

Abstract

The North African murine rodent Paraethomys evolved as an anagenetic lineage from the late Miocene until its extinction in the late—middle Pleistocene. A Fourier analysis of the outlines of the first upper and lower molars of this rodent was used to quantify the evolutionary patterns of this lineage and to compare evolutionary patterns to the climatic record. Morphological evolution and long-term environmental variations are strongly correlated. A change in molar shape, which may be related to the development of a more grass-eating diet, corresponds to the global cooling beginning around 3 Ma and the subsequent increase in aridity in North Africa. Concurrently, size increased, which may be related to increased masticatory efficiency or to metabolic adaptation to the cooler environmental conditions according to Bergmann's rule. This adaptive response to changing environmental conditions corresponds to an acceleration of evolutionary rates in the lineage. The modalities of the evolutionary response in size and shape are probably controlled by intrinsic factors such as different genetic determinisms for both characters.