Brain size is not correlated with forelimb dexterity in fissiped carnivores (Carnivora): A comparative test of the principle of proper mass.

To test the hypothesis that brain size and forelimb dexterity are positively correlated, the relative brain size of 41 species of fissiped (terrestrial) carnivores (Order: Carnivora) was examined with respect to their forelimb use during feeding. With the use of a newly derived dexterity index, the forelimb dexterity executed by each of the species was calculated as a single, continuous variable which was then regressed against the residuals of brain size. To account for confounding effects of phylogenetic inertia, the analysis was performed with independent contrasts analysis using a speciational model of evolutionary change (i.e. equal branch lengths). The results suggest that relative brain size and isocortex size are not correlated with the dexterity of the proximal or distal segments or a combination of the two (total forelimb dexterity). The presence of species with widely different brain sizes and similar dexterities, and vice versa, suggests that an increase in the amount of neural substrate might not be necessary for the production of finely coordinated forelimb movements. It is suggested that this outcome is representative of the plasticity of both mammalian brain size and behavior and that variations in brain size and forelimb dexterity could be linked to disparate ecological and phylogenetic factors which act in concert to promote or constrain neural development and behavior in different species.