Organophosphatic brachiopods: Patterns of biodiversification and extinction in the early Palaeozoic

From a database of 226 Cambrian - Ordovician genera of organophosphatic-she Iled brachiopods comprising the Subphylum Linguliformea, 11 sets of morphol ogical characters typify all orders and superfamilies. Seven sets of these large-scale evolutionary novelties were established already by the end of t he mid Cambrian, 2 more by the end of the late Cambrian, and the remaining 2 before the end of the Arenig. The earliest linguliformeans are of Tommoti an age and represent some of the oldest known benthic organisms with a mine ralised skeleton. Major diversification at the generic level took place dur ing the mid and late Cambrian, by which time members of the Order Lingulida spread from near-shore to deep-water environments and became dominant in l ow diversity benthic assemblages that inhabited mobile sandy bottoms. There was a significant decline in diversity of linguliformeans during the lates t Cambrian. Following recovery in the late Tremadoc-early Arenig, they then became one of the most distinctive components of benthic assemblages inhab iting marginal environments, e.g. eutrophic basins, shallow mobile sands, a nd abyssal depths. During the Llanvirn, there was a significant, worldwide turnover in linguliformean brachiopod faunas, when the majority of epibenth ic lingulides of the families Obolidae, Zhanatellidae and Elkaniidae became extinct and were replaced, in shallow marine biofacies, by assemblages dom inated by bivalved molluscs and burrowing lingulides. There is no trace unt il the mid Ashgill of a significant decline of micromorphic taxa in linguli formean assemblages characteristic of outer shelf environments. However, al l siphonotretides, paterinides and most acrotretide genera disappeared towa rds the end of the late Ordovician pre-Hirnantian Dicellograptus anceps Bio zone.