MORPHOLOGY AND EVOLUTION OF THE AZOOXANTHELLATE CORAL GENERA ANOMOCORA AND ASTEROSMILIA

Anomocora and Asterosmilia are two closely related azooxanthellate coral genera. Anomocora has four fossil and five recent species, while Asterosmilia is represented by seven fossil species. The first occurrences of Anomocora are from questionable specimens from the Cretaceous of Texas and the Eocene of Tonga Island in the Pacific, while Asterosmilia is first known from the Oligocene of St. Barthelemy in the Caribbean.

In order to understand how evolution acts on Anomocora and Asterosmilia, and to get a better sense of the relationships between these two genera, their phylogenetic histories were reconstructed. However, corals are notorious for their lack of discrete phylogenetic characters and for their large amount of morphologic variation. Morphometric methods have yielded a better suite of characters that have proven useful in discriminating cryptic coral species. Both characters derived from qualitative inspection and morphometric analysis were used for this study. Initially, the taxa were analyzed using discrete characters only. Morphometric characters were added to the analysis to refine the evolutionary relationships. This was done by first studying the variation in morphology of three closely related species that were found together during the Pliocene and Pleistocene of Central America. The most important morphometric characters used to separate the three species were coded based on the results of Duncan's multiple range tests and a modified version of gap coding. The remaining species were coded for each of the morphometric characters. Cladograms were constructed using Paup 8.0b and were calibrated against the stratigraphic record.

Characters related to corallum shape and calicular shape seem most important in the evolution of the species within Anomocora and Asterosmilia. However, characters related to size (in other words, the number of septa, corallum height, and calicular size) show strong homoplasy (consistency indices less than 0.5). Moreover, heterochrony is a strong factor in the evolution of these two genera with new species resulting from increased or decreased rate of growth.