Late Carnian symbiotic corals

The paper provides evidence of the coral-algal symbiosis among the Triassic (Carnian, ca. 230 Ma) corals living on the patch reefs of the Western Tethys (deposits currently exposed in the Dolomite Alps, Italy). All examined fossil corals exhibited lack of distinct correlation between carbon (δ13C range between 0.81‰ and 5.81‰) and oxygen (δ18O values range between -4.21‰ and -1.06‰) isotope composition of the skeleton which is consistent with similar pattern in modern symbiotic (zooxanthellate) corals. Irrespective of their growth forms, well preserved skeletons of corals from the Dolomites, most frequently revealed regular growth bands typical of modern symbiotic corals (with some notable exceptions). These results support the scenario that the coral-algal symbiosis that spread across various clades of Scleractinia preceded the reef bloom at the end of the Triassic.