THE PALEOZOIC CORALS .1. ORIGINS AND RELATIONSHIPS

The status, origins and relationships of the various groups of Palaeoz oic corals are reviewed. Five orders are currently recognized: Rugosa, Tabulata, Heterocorallia, Cothoniida and Kilbuchophyllida, to which I add the Tabulaconida and Numidiaphyllida. The Rugosa and Tabulata are considered to be broadly monophyletic clades, and the Tabulata are co nfirmed as zoantharian corals. Morphological features, particularly as pects of septal insertion in both groups, are discussed as clues to th eir likely origins and relationships. They are not considered to have had a skeletonized common ancestor, but they may have arisen as separa te skeletonization events from the same broad group of anemones, repre sented by the living Zoanthiniaria. The Rugosa are not considered to b e ancestral to the Scleractinia. The latter, together with the Permian Numidiaphyllida, are considered to have evolved through skeletonizati on events among a group of anemones derived from the Actiniaria/Corall imorpharia, a member of which also gave rise to the Kirbuchophyllida i n the Ordovician. The pattern of septal insertion in the Heterocoralli a is controversial and the relationship of these corals to contemporar y coral groups remains uncertain. The increasingly important record of Cambrian coralomorphs is assessed, and considered to include several genera of zoantharian corals. However, although similarities are appar ent, none is regarded as directly ancestral to the post-Cambrian coral clades. The history of diversification and extinction of corals throu gh the Palaeozoic is briefly reviewed.