Faunal Realms in Jurassic and Cretaceous Belemnites

Abstract

The extent and characteristics of three faunal realms that can be recognized for Jurassic and Cretaceous belemnites are given here in summarized form accompanied by eight world maps showing occurrence and migration routes. The Boreal and Tethyan realms parallel Arkell9s realms for Jurassic ammonites, but no equivalent for the ammonite Pacific realm has been discerned for the belemnites. They apparently are divided, partly in the Boreal and partly in the Indo-Pacific. The boundary between the Boreal and Tethyan realms was a distinct and stable one, probably influenced by climate. The boundary between the Tethyan and Indo-Pacific realms varied considerably in the upper Jurassic and lower Cretaceous. It is postulated that belemnite migration must have been subject to some form of control, which could have been that, while free swimmers themselves, their prey was confined to shelves and therefore deep-water areas would be barriers. In the discussion statements on delimitation of realms, influence of barriers on migration, and temperature effects are challenged.