Life on the Shell: Conularids and Bivalves/brachiopods in Lower Ordovician (fezouata Shale, Morocco)

Conulariids, an extinct group of Paleozoic cnidarians, reached the peak of their diversity during the Ordovician period. Despite over a century of study, their lifestyle remains subject of debate: were they anchored to the seafloor, or did they drift actively within the water column? In recent decades, the consensus has shifted toward a sessile, benthic mode of life. Yet a key aspect of their biology remains unresolved—the nature of their attachment to the substrate. Direct evidence is rare, with only a handful of specimens preserving holdfast structures comparable to those of their distant relatives, the sphenothallids. New insights come from the Lower Ordovician Fezouata Shales of Morocco, where layers preserving a low-diversity community have been discovered. This community is dominated by the bivalve Babinka sp., the brachiopod Sedlecilingula sp., and the small conulariid Eoconularia sp. Notably, one or more Eoconulariathecae are frequently found attached to the shells of these organisms, often arranged in distinctive V-shaped clusters. This pattern reveals a pioneer, autochthonous community in which both living and dead bivalve or brachiopod individuals provided rare hard substrates on an otherwise soft, unconsolidated seafloor—offering compelling evidence for how conulariids enchored themselves in their environment.