EVOLUTIONARY PATTERNS IN THE REEF CORAL SIDERASTREA DURING THE MIO-PLIOCENE OF THE DOMINICAN REPUBLIC

The theories of punctuated equilibrium versus phyletic gradualism are evaluated in a long continuous sequence in the Mio-Pliocene of the Dominican Republic. The common, shallow water massive reef coral genus Siderastrea was selected for analysis. Geometric morphometrics is used to determine if species exhibit stasis or gradual evolutionary change over approximately 5 million years of geologic time. 100 samples were collected from 5 river exposures, Rio Cana, Rio Gurabo, Rio Mao, Rio Yaque del Norte, and Arroyo Bellaco. These sections were located on previously constructed stratigraphic sections (Saunders et al., 1986). Depositional environments were determined using lithology and sedimentary structures as well as associated corals, mollusks, and ostracodes. Roughly 30 homologous landmarks per corallite on 6 corallites per colony were used to analyze the shape variation of structures within the corallite (i.e. corallite wall, septa, columella, etc.). The variation in corallite shape was then analyzed statistically using multivariate analyses to distinguish species and patterns of variation within species. These multivariate analyses included Principal Component Analysis (PCA) and cluster analysis. To guide in species discrimination, thin-sections of modern species and types were also measured and analyzed.

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