EVOLUTION OF THE NEOGENE CARIBBEAN REEF CORAL STYLOPHORA: ANALYZING MORPHOLOGIC CHANGE WITHIN SPECIES

Morphometric methods are used to examine evolutionary patterns within the common branching reef coral Stylophora in the Miocene and Pliocene of the northern Dominican Republic. The punctuated or gradual nature of the Stylophora evolution is evaluated by analyzing morphologic variation within and among species. Specimens were collected from exquisitely preserved, continuous sequences along Rio Cana, Rio Gurabo, Rio Mao, and Rio Yaque del Norte. The collected specimens were found in fossiliferous calcareous silts within the Baitoa (nn4-6), Gurabo (nn11-12), and Mao (nn14-15) Formations, and range in age from 17.3 - 3.4 Ma. 60 well-preserved specimens were selected from a large collection of samples in which five species were qualitatively identified within the genus Stylophora. Linear based morphometric techniques are used to distinguish morphospecies. Roughly 10 distinct characters are measured including corallite diameter, number of septa per corallite, wall structure, and branch thickness. These characters are analyzed using exploratory multivariate statistical techniques, such as principal component analysis (PCA) and cluster analysis, and also using univariate statistical techniques such as ANOVA. In addition, variation within these morphospecies is analyzed over one million year time intervals.

Preliminary work suggests that species of Stylophora overlap morphologically. Morphologic variation within species was environmentally based, and evolution within the genus follows the punctuated equilibrium model.