Palaeobiogeography of the Middle Jurassic protoglobigerinids (Foraminifera)

The palaeogeographical distribution of the Middle Jurassic protoglobigerinids is discussed using three maps, which correspond to the Aaleno-Bajocian, Bathonian and Callovian intervals. During these intervals small, thin-walled species are found in epicontinental areas, as well as in the Tethys, while the large, occasionally thick-walled taxa were restricted to the Tethyan area. In the Callovian large forms could migrate into the deeper basins of the epicontinental area. In the Aaleno-Bajocian the thick wall of some tests may represent a crust (late stage calcification) because protoglobigerinids with the same external morphology, but different wall thickness, can be found in the Bajocian and the Bathonian. This phenomenon is generally interpreted as a deep water character in planktonic foraminifera. Some taxonomic problems related to morphology are also discussed.