First bryozoan fauna from the Eocene–Oligocene transition in Tanzania

Records of Cenozoic tropical bryozoan faunas are sparse, particularly from Africa. Here we describe a previously unknown bryozoan ‘sand fauna’ from a drill core across the Eocene–Oligocene boundary from a hemipelagic clay succession in Tanzania. Although low in diversity, this well-preserved fauna includes four cheilostome species, all new to science: Heteractis tanzaniensis sp. nov., Bragella pseudofedora gen. et sp. nov., Lacrimula kilwaensis sp. nov. and L. crassa sp. nov. The four species vary in mineralogy, with H. tanzaniensis having an entirely aragonitic skeleton, B. pseudofedora being bimineralic and the two species of Lacrimula calcitic. These species have either free-living ‘lunulitiform’ (H. tanzaniensis) or rooted ‘conescharelliniform’ (B. pseudofedora, L. kilwaensis and L. crassa) colonies adapted to life on a soft, unstable seafloor. The peak occurrence of bryozoans in the core coincides with the Eocene–Oligocene Glacial Maximum (EOGM), characterized by global environmental change from a greenhouse to an icehouse world, sea-level fall, cooling of the oceans and changes in water circulation that may have led to enhanced nutrient levels favourable to bryozoans both in Tanzania and elsewhere.