Morphological variation and homoplasy: the challenge of Paleozoic coral systematics

Abstract

The extinct Paleozoic coral groups Rugosa and Tabulata suffer from confused systematics because of extreme morphological variation, pervasive homoplasy, and relatively simple skeletal morphology. Morphological variation occurs within individuals or colonies, between individuals within a population, and between populations. Variation at each level may have both genetic and ecologic components. Homoplasy is very abundant and extended sequences of parallel or convergent character transformations have led to the recognition of “recurrent evolutionary trends” in many lineages.Morphological variation causes much difficulty in the recognition and characterization of coral species and homoplasy is problematic for phylogeny reconstruction. Improved coral systematics require a more holistic approach to both taxonomy and phylogeny analysis, including: 1) population-based species concepts, as opposed to typological approaches; 2) use of more quantitative techniques in species discrimination and description; 3) more attention to subtle morphological elements, such as microstructure; 4) description of ecological settings (depositional environments) to aid in analysis of behavior and to help unravel ecophenotypic plasticity; and 5) use of stratigraphic and geographic distribution data in phylogeny analysis, because skeletal morphology is inadequate by itself.