Major Events in Foram Evolution
(To learn more about the Geologic Time Scale, visit the Berkeley site linked below)
Early Cambrian (~525 million years ago)
Forams first appeared in the rock record. Earliest specimens were agglutinated, single-chambered varieties; meaning that the forams created their shell by cementing together tiny particles gathered from the sea floor. All species were benthic (bottom-dwelling); however some benthic species moved about on the sea floor while others were stationary either by attaching themselves to the bottom or by burrowing into it.
Late Cambrian (>500 million years ago)
Multi-chambered varieties first evolved.
Devonian (>360 million years ago)
Microgranular and porcellaneous (biomineralized) calcareous tests first evolved.
Middle Pennsylvanian (~308 million years ago)
Forams evolved a hyaline (glassy) calcareous test wall. Additionally, larger foram species first appear, possibly to serve as hosts to symbiotic algae.
End Permian (~250 million years ago)
Mass extinction of most foram species including the large Fusilinids. This extinction is believed to be the largest in Earth's history with 90-95% of all marine species becoming extinct.
Early Jurassic (~183 million years ago)
Planktonic (floating) forams first appear in the rock record. Until this time, all species had been benthic.
Middle Cretaceous (~112 million years ago)
Geographic distribution of planktonic forams begins to expand rapidly.
End Cretaceous (~65 million years ago)
Decrease in planktonic diversity, and extinction of many planktonic foram species. Survivors were generally smaller in size than extinct species. Benthic species were not substantially impacted.
End Paleocene (~55 million years ago)
Extinction of approximately one-half of deep water benthic foram species with an associated decrease in deep water benthic diversity of approximately 30-50%.
Late Eocene to Early Oligocene (~30-39 million years ago)
Numerous smaller extinctions and appearances of benthic foram species throughout this time period, with an marked extinction of many planktonic foram species around 37 million years ago.
Middle Miocene (~12-19 million years ago)
Major planktonic and benthic foram species composition and abundance changes are documented for the middle Miocene. Modern benthic foram varieties evolve.
More than 10,000 foram species are living today. The vast majority of these are benthic; only about 40-50 species are planktonic. Benthic forams today are nearly identical to the suite that evolved in the middle Miocene
Return to Foram Evolution
Geologic Time Scale University of California at Berkeley geologic time scale with links to individual time periods. Pages for individual time periods have a summary, subdivisions of the time period and additional buttons leading to fascinating summaries about the stratigraphy, ancient life, localities and tectonics.
Smithsonian Photos illustrating dramatic size differences of foram species before and after the Cretaceous 65 mya extinction event.
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Culver, S. J. (2003). Benthic foraminifera across the Cretaceous-Tertiary (K-T)boundary: A review. Marine Micropaleontology. 47(3-4), 177-226.
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Lee, J. J. & Anderson, O. R. (1991). Symbiosis in foraminifera. In Lee, J.J. & Anderson, O.R. (Eds.), Biology of Foraminifera. (pp. 157-220). London: Academic Press.
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Ogg, J. (2004). Overview of Global Boundary Stratotype Sections and Points (GSSP's). Retrieved Oct. 26, 2004 from http://www.stratigraphy.org/gssp.htm.
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Prothero, D.R., Ivany, L.C. and Nesbitt, E.A. (1999, August) The Marine Eocene - Oligocene Transition. Retrieved Dec. 11, 2004 from http://www.geosociety.org/penrose/99pcrpt4.htm.
Sen Gupta, B. K. (1999). Introduction to modern Foraminifera. In Sen Gupta, B.K. (Ed.), Modern Foraminifera (pp. 3-6). Dordrecht, Netherlands: Kluwer Academic Publishers.
Scott, D. B., Medioli, F. & Braund, R. (2003). Foramininfera from the Cambrian of Nova Scotia: The oldest multichambered foraminifera. Micropaleontology. 49(2), 109-126.
Revised on: January 15, 2005