Origins and relationships of Paleozoic coral groups and the origin of the Scleractinia

Abstract

Two major groups of corals have essentially continuous records from the Early Ordovician (Tabulata) and Middle Ordovician (Rugosa) to the end of the Permian. A third major group, the living Scleractinia, range from Middle Triassic to Holocene. Additional groups have shorter ranges within the Paleozoic. The origins and relationships of these groups have been discussed for over 100 years. Relations between the Rugosa and Scleractinia have attracted the greatest interest because of their morphologic similarities and the time sequence. Arguments involve the significance of serial versus cyclic septal insertion, calcitic versus aragonitic skeletal mineralogy, and the time gap between the last rugosans and first scleractinians (there are no known Lower Triassic corals). Discussions of relationships among the various Paleozoic groups are commonly based on detailed morphological comparisons because of their overlapping stratigraphic ranges.Recent work on the living corals and anemones supports a closer relationship between groups than is suggested by placing them in different orders or suborders. The paleontological record of “anemones” is slight, but it is reasonable to assume that one or more groups of skeletonless zoantharians persisted through long parts of the Phanerozoic. It is suggested that the major groups of zoantharian corals originated through the development of skeletons in various anemone groups at several different times.