Patterns of size and shape differentiation during the evolutionary radiation of the European Miocene murine rodents

Fourier analysis applied to the outlines of the first upper and lower molars of European Miocene murine rodents was used to quantify the size and shape variations associated with their radiation and to determine the evolutionary relationships among the taxa. The results suggested the occurrence of two lineages involving different evolutionary patterns. Size exhibits a rapid diversification in both lineages, probably because of selective pressures related to increasing competition among species. With regard to shape, one of the lineages is characterized by a conservative morphology, and the other by a tooth evolution oriented toward broader molars, which is interpreted as an adaptive specialization. Size and shape evolution are diversely associated during the radiation, and they may be related to the morphological differentiation of co-existing species and the avoidance of interspecific competition.