Diversity fluctuations and biogeography of Ordovician brachiopod faunas in northeastern Spitsbergen

Investigations of Lower and Middle Ordovician brachiopods in northeastern Spitsbergen have revealed strong ties to faunas in North America and Greenland at the generic level, although the fauna appears mostly endemic at the species level. During the early Palaeozoic, the archipelago of Svalbard, including Spitsbergen, was located at equatorial latitudes along the northeastern margin of Laurentia. The northeastern part of Spitsbergen experienced significant sea level changes, changing from very shallow water in the Tremadocian to deep water in the Floian and slowly back to shallow- water carbonate environments in the Middle Ordovician. The Tremadocian and early Floian brachiopod fauna was of low diversity with a high proportion of cosmopolitan warm-water related rhynchonelliform genera. In the late Floian there was an abrupt diversification event, taking place against the background of the increasing isolation of Laurentia, leading to a diverse, mostly endemic fauna. This diverse fauna remained into the Middle Ordovician. A similar diversification event has been recorded in North America, but here it occurs later, in the Dapingian. The diachroneity of brachiopod diversification within different parts of a continent has previously been shown for South China, suggesting that it may be a common phenomenon. In contrast to the mostly endemic Middle Ordovician rhynchonelliform genera, the linguliform brachiopods included many genera with a wide distribution. This difference is attributed to their different dispersal strategies.