EVOLUTIONARY PALEOECOLOGY OF THE DISCOIDAL BODY FORM WITHIN SUBCLASS RUGOSA, ORDER SCLERACTINIA, AND SCLERACTINIAMORPHS (CLASS ANTHOZOA)

Corals of classes Rugosa and Tabulata are diverse members of Paleozoic reef communities that went extinct during the collapse of reefs at the end-Permian. Corals of the order Scleractinia appear in the Middle Triassic, with similar morphologies and levels of skeletal complexity to subclass Rugosa. Current practice indicates that corals from Paleozoic strata belong to subclass Rugosa while corals from Middle Triassic and younger rocks belong to Scleractinia. However, recent molecular data indicate that the scleractinian clade was present during much of the Paleozoic. Furthermore, skeletonized specimens known as scleractiniamorphs occur in Ordovician and Permian rocks and display septal morphologies apparently similar to those of order Scleractinia. It is hypothesized that scleractiniamorphs may represent possible skeletonized scleractinians before their accepted appearance. Other hypotheses state that scleractiniamorphs may represent aberrant rugosans or another skeletonized anthozoan lineage closely related to Scleractinia. This work aims to test an evolutionary palaeoecological hypothesis related to morphologies present in Rugosa, Scleractinia, and scleractiniamorphs.

The discoidal form is the most prominent corallite shape among scleractiniamorph specimens. Discoidal morphologies also appear within Rugosa and Scleractinia. This study aims to compare the geographic occurrences of discoidal rugosan corals, Triassic and modern scleractinians, and scleractiniamorphs. A list of discoidal taxa was compiled from literature and occurrence data were downloaded from the Paleobiology Database. Geometric morphometrics was used to constrain the discoidal morphology. Gplates and ArcGIS were used to reconstruct paleocoordinates, compare paleolatitudes and paleolongitudes of specimens through time, and perform standard distance analysis. Analyzing geographic ranges across the Paleozoic, Triassic, and modern may reveal environmental preferences among rugosan, scleractinian, and scleractiniamorph taxa sharing the discoidal morphology.