Homologies of Molar Cusps and Crests, and Their Bearing on Assessments of Rodent Phylogeny

Abstract

Evidence for phylogeny derives basically from morphological comparisons, whether of the structure of protein molecules, chromosomes, skulls, or, in the case of paleontological material, mainly teeth. The concept of homology arises from the recognition that some resemblances are more significant than others that are superficial or accidental. It is necessary to decide, when comparing two species, which structural element in one species should be compared with an element in the other. Such corresponding structures in different animals are given the same name (Gr. homos, same; logos, word), and resemblances and differences between them form the raw data on which phylogenetic hypotheses are based. Whether resemblances are due to inheritance from a common ancestor, or whether they have been produced by parallel evolution, is a question that can be decided only after considerable investigation, if at all. Therefore, in this paper I will use the term homology in its etymological sense, to mean morphologically comparable structures, whether or not their resemblance is due to common ancestry.