Palaeoecology of the Devonian ‘button coral’ Microcyclus (Anthozoa: Rugosa) and its recent functional analogues

Abstract Corals exhibit significant phenotypic flexibility in response to various environmental conditions. As a result, the presence of similar morphologies across modern and extinct corals is commonly independent from phylogenetic links. Among the recurring body plans, one particularly distinctive, ‘button coral’ morphotype is observed in the Palaeozoic, free-living, solitary rugose coral genus Microcyclus . This study focuses on Middle Devonian assemblages of the genus Microcyclus from two sites in southeastern Morocco: a carbonate-ramp succession exposed at Madène el Mrakib and a fore-reef succession of the Aferdou el Mrakib reef, which was affected by recurring mass flows of reef-derived debris. The study discusses the habitat preferences, life-history strategies, and potential degree of automobility of this genus based on analyses of their morphology and comparison with modern Scleractinia inhabiting similar environments. The ‘button coral’ morphology of Microcyclus , including the small, discoid corallite with protruded septa, and its inferred preference for habitats with low sedimentation rate point to the adaptation of the genus to living on the sediment surface in soft-bottom settings. Among modern free-living scleractinians, morphologically closest to Microcyclus appear to be Cycloseris boschmai and Cynarina macassarensis , the latter particularly notable for the presence of epitheca, a feature shared with the rugose corals. The morphological constraints indicate that Microcyclus was likely a lithosessile organism with the ability to excavate from a small amount of sediments.