Paleozoic foraminifera

The approximately 300 million years that make up Paleozoic time saw the evolution of eight of the fifteen recognized suborders of Foraminifera. Of the suborders present in the Paleozoic, seven are morphologically relatively simple, slowly evolving, and continued into Mesozoic and Cenozoic times to become the ancestoral lineages from which evolved several additional post-Paleozoic suborders. In contrast, an eighth Paleozoic suborder, the Fusulinina, was an abundant, ecologically dominant group that evolved from simple to highly specialized forms and had a history of rapid evolution with diverse lineages. Fusulinines became extinct at the end of the Paleozoic. Their early representatives may have given rise to three and eventually four post-Paleozoic suborders. A number of suborders in the Paleozoic have similar, supposedly independent, early evolutionary patterns with the following series of morphological steps: (1) single chambers with or without apertures depending on the amount of wall cement; (2) groups of chambers that appear to be buds or aggregations of individuals rather than true chambers; (3) a proloculus followed by a tubular second chamber that is first erect and gradually evolves into enrolled free-living individuals; (4) development of constrictions in the tubular chamber; and finally (5) evolution of true chambers. These morphological steps, which are basic organizational steps with evolutionary significance, appear in lineages with quite different test compositions and, therefore, are considered only distantly related in the present classification.