THE PALEOZOIC CORALS, II - STRUCTURE, VARIATION AND PALEOECOLOGY

Palaeozoic coral faunas were dominated by two orders of Zoantharian co rals, the Rugosa and the Tabulata. Almost all rugose and tabulate cora ls developed an epitheca or holotheca around the corallum and possesse d small to minute attachment scars. A limited number had an encrusting life style and many others could facultatively encrust to some extent when settling by chance on a hard substrate. However, most were effec tively free living on a soft substrate as mature coralla. A high perce ntage of rugose corals were solitary and of the colonial genera, few e xhibited physical integration of modules within the colony. In contras t, most of the exclusively modular tabulate corals possessed some degr ee of integration. Colony formation in tabulate corals was, with doubt ful exceptions, solely by non-parricidal increase, whereas both non-pa rricidal and parricidal increase, the latter in a minor role, occur in the Rugosa. The sources of variation in solitary and colonial Palaeoz oic corals are reviewed and data on growth rates, measured on the basi s of cyclomorphic variation expressed as density band couplets, are as sessed. Growth-form variation in solitary corals and its relationship to stability on the substrate are explored. Growth strategies in colon ial corals are described and their adaptive success under different en vironmental conditions is discussed. Colonial growth-forms were a func tion of the interaction between growth strategy and prevailing conditi ons during astogeny, although some species had genetically constrained , relatively invariate growth-forms. Factors controlling the distribut ion of Palaeozoic corals in the environment - substrate and turbidity, water energy, depth, Light, temperature and variations in salinity an d oxygenation - are reviewed. Palaeozoic coral diversity was much lowe r than that of Recent hermatypic scleractinian corals in comparable en vironments. Most Palaeozoic corals were adapted to soft substrates in warm, shelf seas, and made a limited contribution to reef frameworks. It is concluded that none of them developed a symbiosis with algae in contrast to zooxanthellate scleractinian corals.