CLARIFYING THE ORIGIN OF ORDER SCLERACTINIA (CLASS ANTHOZOA, SUBCLASS HEXACORALLIA)

Corals of the subclasses Rugosa and Tabulata appeared in the fossil record of the Middle Ordovician and disappeared in the End Permian mass extinction. After a gap in the Early Triassic, order Scleractinia appeared in the Middle Triassic. Molecular data, however, indicate that Scleractinia could have originated as early as 445 mya¹. I aim to clarify the origin of order Scleractinia by defining skeletal morphological traits of taxonomic importance using ‘basal’ groups defined by the most recent molecular revision of Scleractinia. I also aim to examine specimens known as ‘scleractiniamorphs’, which have been identified as potential evidence of skeletonized scleractinians within Paleozoic strata.

I will test the hypothesis that the skeletal morphology of scleractiniamorphs is more similar to the morphology of order Scleractinia than to the morphology of subclasses Rugosa or Tabulata. The initial stage of this study includes photography and examination of scleractinian, tabulate, and rugosan coral specimens from museum collections. Important morphological features to be examined include corallum shape, corallite separation, number of septae, and axial structure. I will document dissepiments, tabulae, trabecular structures, and septal insertion schemes which can be examined on available specimens. Data will be analyzed using multivariate statistics to identify morphological similarities among corals. This work will allow a glimpse into the morphologic variation expressed within scleractiniamorphs and among Scleractinia and Rugosa with Tabulata as an out-group. Overall, my work aims to study the classifications of scleractiniamorph specimens and the origins of order Scleractinia.

1. Stolarski, J., Kitahara, M. V., Miller, D. J., Cairns, S. D., Mazur, M., & Meibom, A. (2011). The ancient evolutionary origins of Scleractinia revealed by azooxanthellate corals. BMC Evolutionary Biology, 11(1), 316. https://doi.org/10.1186/1471-2148-11-316