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Science Olympiad
Phylum Sarcomastigophora
Amoebas and their relatives, including foraminifera and radiolaria, belong to the subphylum Sarcodina. Foraminifera and radiolaria have skeletons that readily fossilize, which make them an important part of many micropaleontological samples. Both foraminifera and radiolaria have fossil records that date back to the Cambrian.

Foraminifera are amoeba-like protists that build shells called tests. The shell is referred to as a test because some of the protoplasm of the unicellular organism covers the outside of the test. Tests have chambers that are added as the cell grows. Shells or tests can be made of sand and bits of discarded shells that adhere to an exuded sticky substance, a hard keratin-like material, or calcite (calcium carbonate).

Foraminifera can be planktonic or benthic. Many tropical beaches are composed of sands made primarily from the skeletons of benthic foraminifera. Much of the ocean floor that is less than 4.000 m deep is covered by calcareous ooze composed of microfossil shells made of calcite. Forams that secrete tests of calcite are not typically found below this depth because their skeletons dissolve. The calcite compensation depth (CCD) is the depth at which calcite dissolves and is typically 4,000 to 5,000 meters. Below this depth forms that construct their tests from cemented grains of sand or other foreign particles are more common.

Foraminifera move, feed, and excrete waste using pseudopodia or cell extensions that project through pores in their tests. Foraminifera are a key part of the marine food chain. They ingest smaller microorganisms and detritus; in turn, formams serve as food for larger organisms.
Some forams, like the extinct nummulitids and fusulinids, possess symbiotic algae (photosymbionts).

The deposition of calcium carbonate from nannoplankton and foram shells over long periods of time formed many Late Cretaceous deposits of white, fine-grained limestone known as chalk (Curtis, 1980, p. 370).
The White Cliffs of Dover and other Late Cretaceous chalky deposits around the world are made primarily from coccolithophores, with forams taking on a secondary role (Prothero, 2007, p. 175). Coccolithophores, known as calcareous nannoplankton, are calcifying protists in the phylum Haptophyta. Coccolithophores are one of the major primary producers making up a significant portion of the phytoplankton. In today's oceans coccolithophores are also responsible for half of all calcium carbonate precipitation, thus they are central to the global carbon cycle (De Vargas, Aubry, Probert, & Young, 2007, p 251).

From the Cambrian to the present, forams have played an important role in the marine biosphere as a key part of the food chain. Because their shells (tests) have evolved over time it is possible to use them for correlating rock strata. In fact, more paleontologists specialize in foraminifera than any other fossil group (Prothero, 1998, p. 190). As fossils, forams have multiple uses:

  • planktonic forams are the standard for correlating Mesozoic and Cenozoic marine strata
  • fusulinids are the main index fossil for the late Paleozoic
  • their sensitivity to temperature, chemistry and depth allow them to be used as clues to past climates and marine depositional environments. This last use is critical to the search for oil deposits.

Radiolarians are amoeba-like protists that build an internal skeleton out of opaline silica. The delicate geometric shapes of these tests may remind one of snowflakes or even Christmas ornaments. Radiolarians are typically half the size of forms and are strictly planktonic, none are benthic. Rigid and flexible pseudopodia protrude from the silica skeleton. Some of the pseudopodia are sticky and are used to capture and ingest coccolithophorids, diatoms, bacteria, and other plankton. Like forams, some species of radiolaria posses symbiotic algae. Radiolaria, like forams, are an important food source for many larger organisms.

In tropical ocean floors below the CCD calcareous foraminifera and nannofossils are dissolved away, leaving a siliceous ooze formed from the silica shells of microfossils. These siliceous sediments are called radiolarites. When radiolarites turn to rock they form chert.

Radiolria fossils provide clues for determining past climates as well as the temperature, depth, and geography of ancient oceans. Like foraminifera, radiolarians evolved rapidly, accumulating in thick sedimentary deposits. This makes their biostratigraphy very useful. This is especially true for calcium carbonate poor oceanic sediments, such as those formed in the Arctic and Antarctic regions (Prothero, 2004, pp. 201-206).

Science Olympiad Fossil Event

The 2016 Science Olympiad Fossil list includes two types of forams, Nummulites (Latin: nummulus for "little coin" in reference to their shape) and Fusulinids. The Egyptian Pyramids are constructed of Eocene aged nummulitic limestone. Forams are in the Kingdom Protista, Phylum Sarcomastigophora, and the Order Foraminiferida (Olney, 2008, Foraminifera page). To learn more about Foraminifera read Foram Facts. Fusulinids are similar to wheat grains in shape and size. The fusulinids in the limestone below are most likely in the genus Triticites from the Latin for wheat tritic and the English for rock or fossil ite (Borror, 1988, pp 50 and 105).

Fusulinid Triticites
Missouri, USA
Fusulinid Range Carboniferous-Permian

Nummulites sp.
Lake Formation
Punjab, West Pakistan



Orbitoides sp.
Upper Cretaceous
ENCI Quarry
Maastricht, The Netherlands
5 mm diameter
Image at 20x



Orbitoides sp.
Upper Cretaceous
ENCI Quarry
Maastricht, The Netherlands

7 mm diameter
Image at 10x

2 cm diameter

1 cm diameter

Foram at 40x
Unknown Location

1000 microns in diameter

Triticites in Cross-Section

Fusulinids in Cross-Section
Florence-A chert
Kay County, Oklahoma

Click on Image to "zoom-in"


Borror, D.J. (1988). Dictionary of Word Roots and Combining Forms. California: Mayfield Publishing Company.

Curtis, H. (1980). Biology. New York: Worth Publishers, INC.

DeVargas, Aubry, Probert, & Young. (2007). Origin and Evolution of Coccolithophores: From Coastal Hunters to Oceanic Farmers. In Falkowski, P.G. Knoll, A.H. [Eds] Evolution of Primary Producers in the Sea. (pp. 251-285). China: Elsevier Academic Press.

Griem, W. (2007) Museo Virtual:

Olney, M. (2008). MIRACLE: Microfossil Image Recovery and Circulation for Learning and Education: University College London. See:

Prothero, D.R. (1998). Bringing Fossils to Life: An Introduction to Paleobiology. New York: McGraw-Hill.

Prothero, D.R. (2004). Bringing Fossils to Life: An Introduction to Paleobiology [2nd edition]. New York: McGraw-Hill.

Prothero, D.R. (2007). Evolution: What Fossils Say and Why It Matters. New York: Columbia University Press.

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