Fossil group

Planktonic foraminifera (Globotruncana spp.)

Foraminifera · Jurassic – Recent

Foraminifera that drifted in the open ocean as plankton rather than living on the sea floor. Because they evolved quickly and spread across whole oceans, successive species make excellent index fossils, and their tiny calcite shells rain down to build deep-sea ooze. Their coiling and chamber pattern are used to zone and date marine sediments.

A broad fossil group rather than a single taxon — the units below record it among their fauna or flora.