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 molar s of European Miocene murine rodents was used to quantify the size and shap e variations associated with their radiation and to determine the evolution ary relationships among the taxa. The results suggested the occurrence of t wo lineages involving different evolutionary patterns. Size exhibits a rapi d 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 oth er by a tooth evolution oriented toward broader molars, which is interprete d as an adaptive specialization. Size and shape evolution are diversely ass ociated during the radiation, and they may be related to the morphological differentiation of co-existing species and the avoidance of interspecific c ompetition.