A synopsis of Late Ordovician brachiopod diversity in the Anti-Atlas, Morocco

Abstract

Abstract A detailed overview of the taxonomical composition and diversity of the Late Ordovician brachiopod faunas in Morocco is presented. In addition, based on new brachiopod collections, the lower boundary of the Hirnantian Stage in the Anti-Atlas is constrained. A new, prolonged range of the Hirnantia Fauna in the Anti-Atlas region permits comparison between known Late Ordovician climatic excursions and changes in brachiopod diversity. Despite the late Katian Boda warming event, the Moroccan brachiopod associations remained notably endemic with low diversities throughout the studied interval. Contrary to what is seen in other high-latitude peri-Gondwanan terranes, species richness decreased during the Boda Event. This suggests that the Moroccan shelves experienced a more persistent, colder climate, favouring well-adapted, incumbent faunas that did not respond to this climatic optimum. Lastly, the two phases of Hirnantian extinctions, which globally are correlated with the growth and melting of ice caps, are expressed differently from elsewhere: the first pulse only caused minor disruption, followed by a radiation of the Hirnantia Fauna, whereas the second pulse, related to the subsequent warming phase in the uppermost Hirnantian, caused severe extinctions in Morocco among the opportunistic Hirnantia Fauna.