Supra-Specific Variation in Nature and in Classification from the View- Point of Paleontology

Abstract

Data on supra-specific variation supplied by paleontology and the methods and results of their interpretation are exemplified from the study of the extinct order Notoungu-lata. Within a single group one set of structures may be relatively invariable and conservative while another varies greatly and evolves rapidly. In related groups these 2 tendencies do not necessarily affect the same structures in each group. Rates of evolution are different for different structures and for the same structure at different times. Characters that define supra-specific categories in some instances may in others be only individual variations. Supra-specific characters do not necessarily differ qualitatively or quantitatively from infra-specific but may differ only in their distribution or correlation. Principles of classification are reviewed with special reference to recent criticisms by A. C. Kinsey. It is concluded that supra-specific categories are theoretically natural units based primarily not on discontinuity but on phyletic branching, that their definition need not imply possession of invariable or of common characters, and that the figure of a "tree of life" retains a figurative validity when properly interpreted. The existence of physiological species, of convergence, and of parallelism need not essentially falsify paleontological classification.