Cats and Dogs Down the Tree: The Tempo and Mode of Evolution in the Lower Carnassial of Fossil and Living Carnivora

Abstract

Teeth are usually considered the primer to understand mammalian evolution. Their morphology is the result of the complex interplay between adaptation to food processing and somewhat fixed developmental programs. We analyse the morphometry of the first lower molar (m1 = lower carnassial) in 199 carnivore species (64 extant and 135 extinct) in order to clarify the tempo and mode of evolution of two different and possibly related traits, tooth size and tooth angular height. We applied a set of comparative methods and produced disparity through time plots by using four alternative phylogenetic trees. Three of them include fossil species, and were used in order to estimate what an effect the inclusion of fossil species has on the patterns we found for extant species. Our analyses on living species show that m1 size exhibits a weak phylogenetic signal, and that its variance occurs more within than among clades. The opposite applies to m1 angular height, which evolved in an adaptive radiation-like fashion, showing very strong phylogenetic signal and great among-clade variation. These results are thoroughly confirmed after the inclusion of fossil data. Major differences in m1 shape in Carnivora were clearly established early in their evolutionary history, probably as a result of rapid morphospace occupation after the clade radiation. Successive variation in tooth size allowed species to avoid potential overlap in feeding morphologies as a mechanism to limit interspecific competitive interaction within subclades.