CHRONICLES OF SCLERACTINIAN CORAL FAMILIES: PHYLOGENETIC SIGNIFICANCE OF THE SKELETAL THICKENING DEPOSITS

Thickening Deposits (TD's) traditionally referred to as "fibers" are dominant component of the scleractinian coral skeleton. These cyclically formed structures are, in some geochemical models of coral mineralization, considered as calcium carbonate precipitate from an extra-cellular, supersaturated fluid, close in composition to seawater, whose morphology and arrangement are controlled by inorganic kinetic factors of crystal growth. In contrast to such simplified models, a great variety of TD's patterns is observed in representatives of molecularly distinguished clades. Distinct and consistent microstructural patterns are observed in many of these clades (e.g., flabellids, caryophylliids, acroporiids, pocilloporiids, micrabaciids) irrespective of ecological and physiological conditions. This evidence clearly suggests a prevailing organismal control of structure and composition of TD's, however, phylogenetic and taxonomic value of these structures was underestimated.

The purpose of this presentation is three fold: (1) provide fine-scale, crystallographic characteristics of TD's and propose general model of their morphogenesis based also on experimental data, (2) overview patterns of TD's in extant representatives of major clades of Scleractinia and discuss taxonomic value of this microstructural character, (3) show examples of excellent preservation as well as diagenetic alteration of TD's in fossil corals and overview major patterns in TD's organization since the Triassic until the present.