Abstract

The bihemispherical distribution of Jurassic Ostracoda is examined and considerable numbers of species are shown to occur in both hemispheres, although this total is, for any of the Jurassic stages except the Lower and Middle Jurassic of the southern hemisphere, exceeded by the number of species restricted to either hemisphere. From the known stratigraphical distribution of some of the taxa occurring in both hemispheres it has been possible to reconstruct a migrational history. This shows that, while in the Lower Jurassic almost as many species migrated from the south to the north as vice versa, in the Middle and Upper Jurassic there was apparently no migration from the south and all migration was from the north. The palaeoceanographical circumstances of the Jurassic, a time when a deep, cold psychro-sphere did not exist in the oceans, in relation to the migration of Ostracoda is discussed, as are the likely migration routes available to Jurassic bihemispherical taxa given the existence of the Tethys, and the absence of the North Atlantic and Caribbean as well developed seaways through much of the interval.