Comparative morphology and evolution of the cerebellum in the mammalian order carnivora

It is proposed that the central nervous system and its components, because of their intimate and delicate relationship, to the remainder of the organism, remain free of trivial variation during normal ontogeny but, at the same time, response sensitively to major genetic changes resulting in the divergence of new species. The proliferation and consolidation of such changes should then provide clues to the evolutionary relationship between species and between higher taxa as well. To explore this hypothesis, the gross morphology of the cerebellum is described in detail in 68 species from all families of the mammalian order Carnivora; these are also compared broadly with 31 species representing nine other order of this class. Although there is a wide range of complexity in cerebellar morphology throughout the class and within the order Carnivora, a basic mammalian pattern is evident in all species, viz., three fundamental lobes subdivided into eight midline vermian lobules and four bilateral pairs of lobules in the two hemispheres. Subordinate to this is a hierarchy of trait sets respectively characteristic of each order, family, genus, and species. Within each taxon, these characters are remarkably stable, verifying the original premise. Two principle types of evolutionary statements can be derived from this study, relative to the development of the cerebellum itself as the species become more advanced, and to the phylogenetic connections among recent carnivore species. ..