Abstract
Boreal, Tethyan, and Indo-Pacific faunal realms may be recognized in belemnite faunas of Callovian and most of later Mesozoic time. The presence of such clearly-defined realms indicates restriction of belemnite migration and perhaps the belemnites were confined to the shelves, extensive areas of deep water forming barriers. Migration of belemnites in the Tethyan and Indo-Pacific realms may be explained in terms of deep water barriers, but delimitation of the Boreal realm is thought to be a result of climatic zoning.