Tabulates, subclass or order Tabulata, are extinct corals of anthozoans. Tabulates, unlike rugosans, were always colonial organisms. They have simple calcareous skeleton, colonies consisting of prismatic or tube-like corallites communicating by mural pores or pore channels or tunnels. Polyps lived inside corallites as chambers with base-like tabulae below and septal spines or laminar septa on sides protruding from the corallite wall. Tabulate corals are taxonomically complicated because of their simplicity. Favositids are characterized by closely packed corallites with mural-pores and their morphology is so variable that it differs even within a colony. Heliolitids are more complicated because of their coenenchymal tissue between corallites, which consists of tiny tubes - tubuli or wavy dissepiments. Halysitids are similar with having often coenenchyme, but their corallites are enclosed into ranks of various shape and size. Syringoporids form fasciculate colonies consisting of tubes having little space around and being connected by pore tunnels. Auloporids are reptant forms encrusting other organisms, as a small horny network.
Tabulate corals occurred in the Ordovician Period of America and Siberia, much earlier than in Baltoscandia. The first appearances of tabulates Lyopora, Eoflecheria, Saffordophyllum and Protaraea in Baltica are known from the level of the Oandu Stage. Estonia is rich in Ordovician and Silurian tabulates, which are easy to find in localities of Hiiumaa, Vormsi and Saaremaa. Quarries in mainland are nice places to observe tabulates in their living position.
Tabulates are large, but their finer taxonomy is observed only from peels and thin-sections. Normally pair of thin-sections is made from transverse and vertical directions of colony growth. Peel is an acetate replica from the polished and etched surface of the colony cut. Thin-sections are thin pieces of colonies, clued to glass and grinded down until 50 microns. Their scanned and photographed images are investigated later by using different software.
Role in geology
Tabulates are sessile organisms which preferred only shallow seas and are not mush useful in stratigraphy. They were spread on ancient oceans sporadically or formed bioherms or biostromes. Together with strtomatoporoids, rugosans and other fossils in the same community, they are informative in palaeoecology. Sedimentological processes are readable also from the shape and growth details of such organisms.