Azooxanthellate colonial corals from the Miocene Omori Formation, Shimane, Japan

Azooxanthellate colonial corals are important habitat-formers in deep-water ecosystems. Here, we provide detailed descriptions of three framework-forming azooxanthellate corals (Petrophyllia niimiensis, Dendrophyllia okamotoi and Dendrophyllia mokiensis sp. nov.) from the Miocene Omori Formation on the Moki coast in Oda, Shimane, Japan using microfocus X-ray computed tomography. With an estimated age of 17.65–13.60 Ma based on nannofossils, Dendrophyllia mokiensis sp. nov. represents the oldest member of Dendrophyllia with a sympodial budding colony. Moreover, this is the first report of the co-occurrence of Petrophyllia and Dendrophyllia in a high density fossil assemblage. Petrophyllia has been reported as a framework builder in cold-water coral reefs or a member of dense accumulations of azooxanthellate corals during the Turonian (Late Cretaceous), thereby raising the possibility that an azooxanthellate coral community dominated by Petrophyllia also existed in the Miocene. This discovery sheds light on changes in azooxanthellate coral communities in deep-water coral habitats during the Cenozoic.