Paleontology, Phylogeny, and Classification: an Example From the Mammalian Fossil Record

Gingerich, P. D. (Museum of Paleontology, The University of Michigan, Ann Arbor, Michigan 48109) 1979. Paleontology, phylogeny, and classification: an example from the mammalian fossil records. Syst. Zool. 28:451–464 .—The purpose of a general formal classification of animals is to foster effective communication within and between zoological subdisciplines. Cladistics is a method of classification based only on phylogeny, but knowledge of phylogeny requires a relatively dense and continuous fossil record not available for many groups. Cladistics presumes phylogeny, and it cannot be used to reconstruct phylogeny. Furthermore, phylogenetic relationships are not the only attributes of organisms, and classifications based solely on phylogeny ignore important attributes related to adaption, biogeography, and age. Effective communication requires that a classification be as simple as possible, balanced, and relatively stable. In practice, organisms are grouped into, species, and species are grouped into successively higher taxa primarily on the basis of (1) overall similarity (including morphology, geography, and age), with the boundaries between taxa being drawn in such a way that (2) each group is monophyletic in the general sense of this term, with (3) traditional groupings being maintained to the maximum extent consistent with (1) and (2). Classification is basically phenetic, with phylogeny (where known) providing an important constraint on acceptable phenetic arrangements. Traditional and cladistic classifications of North American Eocene primates of the family Adapidae are compared, with a slightly modified traditional classification being favored because of its simplicity, balance, and stability. Phylogeny itself is better expressed in a diagram than in a formal classification.