Diversification patterns in the clitambonitoid brachiopods of the Ordovician of Baltoscandia

Two intervals of clitambonitoid diversification followed by major extinctions have been recorded in the Ordovician rocks of Baltoscandia, one during the Arenig and a second in the mid Caradoc. The Arenig radiation was characterized by high origination and extinction rates of both genera and species associated with the development of carbonate environments across the region. In addition the migration of numerous stocks of clitambonitoids out of Baltica to a number of other palaeocontinents occurred during this diversity peak during the Arenig, together with the spread of the majority of genera into a range of more local environments. A marked extinction in the Early Llanvirn coincided with shifts in sedimentation patterns whereas the diversity hike in the Mid Caradoc reflects the diversification of clitambonitoid species in both inner and outer shelf environments. The later Caradoc extinction coincided with an extensive eustatic regression event and the major restructuring of the ecosystem and brachiopod fauna. The final extinction of Baltic clitambonitoids in the late Ashgill was gradual and probably reflected an increasing dependence on more restricted niches.