Sometimes new insights in paleontology come from new ideas about known fossils; other times it comes from the discovery of extraordinarily preserved specimens such as Archaeopteryx, Aysheaia and, now, Favosites

The discovery in 1970 of a new subclass Sclerospongia in living reefs in the Pacific and Caribbean was naturally of considerable interest to marine biologists and reef ecologists. Paleontologists, however, were even more excited about this discovery because these coralline sponges seemed to be dead ringers for stromatoporoids -- those problematic calcareous organisms that were the major builder of the great reef tracts of the middle Paleozoic. Detailed work showed that they are indeed close kin. So, previously taxonomic orphans, stromatoporoids have finally found a home in this new subclass of the phylum Porifera.

Stromatoporoids are not the only fossil group thought to be allied with the living sclerosponges. The Tabulata, extinct since the Paleozoic, were simple colonial organisms that secreted a calcite skeleton composed essentially of small tubes with horizontal partitions. The walls of the tubes, which may be in contact, are commonly perforated. The Tabulata have long been considered to be a group of colonial corals, although they are quite different from the extinct rugose corals and the living hexacorals. But some paleontologists have suggested that the Tabulata is another group of Sclerospongia. All living corals and sea anemones possess tentacle-bearing polyps, but because polyp tissue is soft and watery and devoid of means for calcification, it has never been found fossilized. That is, until a few years ago when Paul Copper of Laurentian University in Sudbury discovered a few extraordinarily preserved specimens of the tabulate Favosites in the Jupiter Formation (Early Silurian, 435 Ma) of Anticosti Island in the Gulf of St. Lawrence. These specimens solved the question of the nature and identity of Tabulata because they contain polyps. These Favosites colonies consist of little domes 5-6 cm across; the upper surface displaying crowded, prismatic 'corallites', each about 2 mm in diameter. Virtually every 'corallite' contains polyps preserved as calcite. The polyp is not much more than a millimetre across, but each is seen to include a ring of tentacles inwardly coiled in a retracted position. Each ring of tentacles numbers 12.

Because all corals possess polyps, and sponges do not, the uniquely-preserved polyp-bearing specimens from Anticosti Island demonstrate unequivocally that Favosites and probably all Tabulata are corals. They further imply that Tabulata, with their twelve tentacles stand apart from the tetracorals, hexacorals and octocorals (perhaps they should be called 'dodecacorals').