Phylogeny of the Scleractinia based on Bayesian analysis of concatenated mitochondrial (16S rDNA) and nuclear (28S rDNA) data. The tree shown is the majority rule consensus (BMC) cladogram based on sequence data for 121 scleractinian corals with the corallimorpharian Ricordea florida defined as outgroup. Representatives of the families Micrabaciidae and Gardineriidae form the basal clade within the Scleractinia, their divergence predating that of the Complexa and Robusta clades. To estimate divergence times for gardineriids/micrabaciids and other scleractinians, a relaxed molecular-clock (uncorrelated lognormal) Bayesian Markov chain Monte Carlo method was applied. The clock was calibrated using the earliest fossils that can be unambiguously assigned to extant clades and whose unique skeletal characters can be unequivocally recognized in fossil coralla (grey box identify each calibrated node and their respectively earliest fossil dates). Dates in red are discussed in the text. Asterisks (*) beside nodes indicate Maximum Likelihood (Chi-square and Bootstrap) and BMC (posterior probability) support greater than 0.95, 70, and 95 respectively, whereas a plus (+) indicates support higher than 0.80, 55, and 80 respectively. For each family/clade examined, the corresponding branches are colour coded. Black circles and/or black squares indicate those species that are colonial and/or zooxanthellate. Bold text indicates species for which sequence data was obtained in the present study. For the various scleractinian families included in the analyses, outlines of coralla for typical representatives (main - distal, and small - lateral/colony views) are shown to the right of the tree.