NEOGENE EVOLUTION OF THE REEF CORAL SPECIES COMPLEX MONTASTRAEA "CAVERNOSA": MORPHOMETRIC ANALYSIS OF VARIATION WITHIN AND AMONG SPECIES

Geometric morphometric methods are used to analyze the evolutionary patterns within the Montastraea “cavernosa” species complex in the Miocene and Pliocene of the northern Dominican Republic. The Montastraea “cavernosa” complex is distinguished by having four or more cycles of septa and a larger corallite (5-9 mm). The nature of Montastraea “cavernosa” evolution is examined by evaluating morphologic variation within and among species. Specimens examined were collected from well-preserved, continuous Mio-Pliocene sequences along several rivers in the Cibao Valley of the northern Dominican Republic. The specimens were found in reefal calcareous siltstones within the Cercado, Gurabo, and Mao Formations. Approximately 95 well-preserved specimens are analyzed. Geometric morphometric techniques and traditional linear measurements are used to distinguish different morphospecies. This approach is similar to that used to distinguish the members of the Montastraea “annularis” complex, which were later confirmed genetically. Two-dimensional Cartesian coordinates are collected for 17 landmarks, measurements are taken of corallite and columella diameter, and the number of septa is counted. The landmarks differentiate homologous points, which define the thickness and structure of the corallite wall and costosepta. The position of these landmarks and linear data are analyzed using canonical variate analysis. The univariate statistical technique, one-way analysis of variance, is also used. Previous work demonstrated that the Montastraea “cavernosa” complex consisted of at least five species in the Dominican Republic during the Neogene. This study indicates that at least eight species belong to the complex during that time period. This study also indicates that most species in the complex differ from each other in a combination of septal number, corallite diameter, and wall thickness. Most species are confined to a single formation (approximately a 2-3 million year duration) and each formation contains numerous species.