Neogloboquadrina dutertrei. (Credit: Dr Kate Darling).
Planktonic foraminifera made their first appearance in the Late Triassic. Although, identifying the first occurrence of planktonic foraminifera is complex, with many suggested planktonic forms later being reinterpreted as benthic. They are present in different types of marine sediments, such as carbonates or limestones, and are excellent biostratigraphic markers.
Their test are made of globular chambers composed of secrete calcite or aragonite, with no internal structures and different patterns of chamber disposition: trochospiral, involute trochospiral and planispiral growth. During the Cenozoic, some forms exhibited supplementary apertures or areal apertures. The tests also show perforations and a variety of surface ornamentations like cones, short ridges or spines.
The phylogenetic evolution of planktonic foraminifera are closely associated with global and regional changes in climate and oceanography.
The evolution of early planktonic foraminifera (From Boudagher-Fadel, 2013)
All species of Late Triassic and Jurassic planktonic foraminifera are members of the superfamily Favuselloidea. They present a test composed by aragonite, with microperforations, and sub-globular adult chambers. After the major End Triassic event, the Jurassic period saw warm tropical greenhouse conditions worldwide. The surviving planktonic foraminifera were usually dominated by small globular forms.
It was suggested that a second transition from a benthic to a planktonic mode of life took place at the Jurassic, which occurred under conditions similar to those that triggered planktonic speciation in the Late Triassic (hot and dry global climate, and low sea levels).
During the Cretaceous, the favusellids must have made the transition from being aragonitic to calcitic. Also, in the Late Aptian there was a significant number of planktonic foraminiferal extinctions, but these were compensated by the establishment of a large number of new genera at the Aptian–Albian boundary.
Planktonic foraminifera from the Sargasso Sea in the North Atlantic Ocean. (Photograph courtesy Colomban de Vargas, EPPO/SBRoscoff.)
The Paleogene assemblage of planktonic foraminifera was derived from the few species that survive the mass extinction event at the end of the Cretaceous.
In the Early Miocene, the planktonic foraminifera were most abundant and diverse in the tropics and subtropics, and after the Mid-Miocene Climatic Optimum, many species were adapted to populate temperate and sub-polar oceans.
During the Middle and Late Pliocene, the final closure of the Central American seaway, changed oceanic circulation and drove a significant number of species extinctions. Most modern, living species originated in the Pliocene and Pleistocene.
References:
Armstrong, H. A., Brasier, M. D., 2005. Microfossils (2nd Ed). Blackwell, Oxford.
Boudagher-Fadel, MK; (2013) Biostratigraphic and Geological Significance of Planktonic Foraminifera. (2nd ed.)
Letters from Gondwana. 