Article: Ostracodes across the Iapetus Ocean

A pilot study comparing ostracode faunas from the North American and European plates dispels the notion that Ordovician ostracodes show strict endemicity. Problems addressed include: how some ostracodes managed to cross the Ordovician lapetus Ocean estimated at 3,000 + km wide; and why some of their ostracode counterparts in the Silurian show provinciality? It is concluded that, from the point of view of ostracode dispersal, opposing Ordovician plates may have been in closer effective geographical proximity than hitherto supposed. Ostracodes recovered only slowly and with general provincial aspect from global sea level changes at the Ordovician-Silurian boundary.Ostracode distributions support other biogeographic evidence that Tornquist's Sea, the ocean between the Gondwanan plate (containing southern Britain) and Baltica, had contracted by mid to late Ordovician and that the Rheic Ocean, separating northern and southern Europe, was developing during the Silurian. Much more work on Lower Palaeozoic ostracodes is needed to test these findings further.