A Late Cenomanian bryozoan biostrome from north-eastern Nigeria

Bryozoans are present in rock-forming abundance throughout a 30-cm thickness of the Late Cenomanian Pindiga Formation at its type locality in north-eastern Nigeria. In addition to representing a rare record of Cretaceous bryozoans from the African continent, the Pindiga bryozoan biostrome provides an exception to the general rule that post-Palaeozoic bryozoan-rich deposits formed only outside the palaeotropics. A single bryozoan species is present, the anascan cheilostomeHeteroconopeum janieresiense (Canu, 1897), originally described from the French Turonian. Colonies are preserved as para-authochthonous branch fragments derived from bushy colonies. The ancestrula and early budding pattern are described for the first time in this genus. Colonies are attached to, and are themselves encrusted by, small oysters. Unlike most cheilostomes, the malacostegan H. janieresiense probably had a long-lived, planktotrophic larva and was tolerant of variable salinities. These factors may explain its occurrence in the upper Benue Trough, an area of intermittent hyposalinity far distant from the main contemporaneous bryozoan populations.