EVOLUTION OF THE CARIBBEAN REEF CORAL MONTASTRAEA CAVERNOSA BY ANALYSIS OF MORPHOLOGIC CHANGE

Geometric morphometric methods are used to analyze the evolutionary patterns within the species complex Montastraea cavernosa in the Miocene and Pliocene of the northern Dominican Republic. The Montastraea cavernosa complex is distinguished from the Montastraea limbata/annularis complex by having four or more cycles of septa and a more complicated columella. The evolutionary histories of these complexes differ greatly. The nature of Montastraea evolution is examined by evaluating morphologic variation within and among species. Previous work demonstrated that the Montastraea cavernosa complex consists of four species. This study suggests that more species may belong to the complex. Specimens examined were collected from well-preserved, continuous sequences along the Rio Cana, Cañada de Zamba, and Arroyo Bellaco. The specimens were found in fossiliferous calcareous silts within the Mao and Gurabo Formations. Approximately thirty well-preserved specimens were analyzed. Geometric morphometric techniques were used to distinguish different morphospecies. Two-dimensional Cartesian coordinates were collected for approximately 27 landmarks. The landmarks differentiate homologous points, which define the thickness and structure of the corallite wall and costosepta. The position of these landmarks is analyzed using multivariate statistical techniques, such as principal component analysis (PCA) and cluster analysis. Univariate statistical techniques, such as ANOVA are also used.