Recognizing species of Late Cenozoic Scleractinia and their evolutionary patterns

Abstract

New morphometric methods for distinguishing morphologically similar species of Recent colonial scleractinian corals involve the analysis of three dimensional landmarks digitized on calical surfaces. Variables suitable for multivariate statistical analysis are derived from the landmark data by applying various geometrical techniques, including Bookstein size and shape coordinates and generalized resistant fitting. Cluster analyses of these variables and study of the relative positions of replicates from the same colony on the resulting dendrograms are used to recognize clusters of colonies representing morphospecies. Comparisons with the results of genetic analyses on the same specimens suggest that these morphospecies correspond closely with biological species.Although slightly less effective, similar analyses of two dimensional landmark data collected on thin sections of the same specimens also distinguish species, and suggest that biological species can be approximated in the fossil record. Multivariate statistical analyses show that variables derived from two dimensional landmarks can be used to trace the stratigraphic ranges of these fossil species. The appropriate method for tracing ranges depends of the evenness of sampling in different geologic horizons. Preliminary comparisons of observed stratigraphic ranges determined by this approach with those determined by cladistic analysis suggest that overall patterns in evolutionary rates through geologic time are the same for both approaches. Thus, nontraditional morphologic characters determined by subsequent examination of morphometrically-defined species have potential for providing sufficient resolution for phylogenetic analysis.