Foraminifera

Taxobox
name = Foraminifera
fossil_range = fossil range|600


image_width = 200px
image_caption = Live "Ammonia tepida" (Rotaliida)
domain = Eukaryota
regnum = Rhizaria
superphylum = Retaria
phylum = Foraminifera
phylum_authority = d'Orbigny, 1826
subdivision_ranks = Orders
subdivision = Allogromiida
Carterinida
Fusulinida - "extinct"
Globigerinida
Involutinida - "extinct"
Lagenida
Miliolida
Silicoloculinida
Spirillinida
Textulariida
"incertae sedis"
Xenophyophorea
"Reticulomyxa"

The Foraminifera, ("Hole Bearers") or forams for short, are a large group of amoeboid protists with reticulating pseudopods, fine strands of cytoplasm that branch and merge to form a dynamic net.cite book|title = Modern Planktonic Foraminifera|year = 1989|last= Hemleben|first=C.|coauthors= Spindler, M.& Anderson, O.R.|publisher= Springer-Verlag|id= |pages = 363] They typically produce a test, or shell, which can have either one or multiple chambers, some becoming quite elaborate in structure.cite book|title = Neogene Planktonic Foraminifera: A Phylogenetic Atlas|year = 1983|last= Kennett|first=J.P.|coauthors= Srinivasan, M.S.|publisher= Hutchinson Ross|id= |pages = 265] These shells are made of calcium carbonate (CaCO3) or agglutinated sediment particles. About 275,000 species are recognized, both living and fossil.Fact|date=February 2007 They are usually less than 1 mm in size, but some are much larger, and the largest recorded specimen reached 19 cm.Fact|date=February 2007

Although as yet unsupported by morphological correlates, molecular data strongly suggest that Foraminifera are closely related to the Cercozoa and Radiolaria, both of which also include amoeboids with complex shells; these three groups make up the Rhizaria.cite journal|title = Protist phylogeny and the high-level classification of Protozoa|year = 2003|last= Cavalier-Smith|first=T.|journal = European Journal of Protistology|volume = 34|issue = 4|pages = 338–348|doi = 10.1078/0932-4739-00002] However, the exact relationships of the forams to the other groups and to one another are still not entirely clear.

Living forams

Modern forams are primarily marine, although they can survive in brackish conditions.cite book|title = Modern Foraminifera|year = 1983|last= Sen Gupta|first=B.K.|publisher= Springer|pages = 384] A few species survive in fresh water and one even lives in damp rainforest soil.Fact|date=February 2007 They are very common in the meiobenthos, and about 40 morphospecies are planktonic. This count may however represent only a fraction of actual diversity, since many genetically discrepant species may be morphologically indistinguishable.cite journal|title = Genetic diversity among modern planktonic foraminifer species: its effect on paleoceanographic reconstructions|year = 2002|last= Kucera|first=M.|coauthors = Darling, K.F.|journal = Philosophical Transactions of the Royal Society of London|volume = A360|issue = 4|pages = 695–718] The cell is divided into granular endoplasm and transparent ectoplasm. The pseudopodial net may emerge through a single opening or many perforations in the test, and characteristically has small granules streaming in both directions.

The pseudopods are used for locomotion, anchoring, and in capturing food, which consists of small organisms such as diatoms or bacteria. A number of forms have unicellular algae as endosymbionts, from diverse lineages such as the green algae, red algae, golden algae, diatoms, and dinoflagellates. Some forams are kleptoplastic, retaining chloroplasts from ingested algae to conduct photosynthesis.cite journal|title = Benthic foraminifera of dysoxic sediments: chloroplast sequestration and functional morphology|year = 1999|last= Bernhard|first=J. M.|coauthors= Bowser, S.M.|journal = Earth Science Reviews|volume = 46|pages = 149–165|doi = 10.1016/S0012-8252(99)00017-3]

The foraminiferal life-cycle involves an alternation between haploid and diploid generations, although they are mostly similar in form. The haploid or gamontAmbiguous link initially has a single nucleus, and divides to produce numerous gametes, which typically have two flagella. The diploid or is multinucleate, and after meiosis fragments to produce new gamonts. Multiple rounds of asexual reproduction between sexual generations is not uncommon in benthic forms. Foramanifera typically live for about a month.cite journal
author = Crowley, T.J.
coauthors = Zachos, J.C.
year = 2000
title = Comparison of zonal temperature profiles for past warm time periods
journal = Warm Climates in Earth History
pages = 50–76
url = http://books.google.com/books?hl=en&lr=&ie=UTF-8&id=GdFd-5TZa6oC&oi=fnd&pg=PA50&dq=Crowley+Zachos&ots=6iR8VGrQ22&sig=e1yoIwRYsRPU15JWI3Kn6RAFYkA
accessdate = 2008-04-24]

Tests

The form and composition of the test is the primary means by which forams are identified and classified.Fact|date=February 2007 Most have calcareous tests, composed of calcium carbonate. In other forams the test may be composed of organic material, made from small pieces of sediment cemented together (agglutinated), and in one genus of silica. Openings in the test, including those that allow cytoplasm to flow between chambers, are called apertures.

Tests are known as fossils as far back as the Cambrian period, [ [http://www.newscientist.com/channel/life/mg19826553.500-sea-creatures-had-a-thing-for-bling.html Sea creatures had a thing for bling - life - 08 May 2008 - New Scientist ] ] and many marine sediments are composed primarily of them. For instance, the limestone that makes up the pyramids of Egypt is composed almost entirely of nummulitic benthic foraminifera. [ [http://www.ucl.ac.uk/GeolSci/micropal/foram.html#histofstudy Foraminifera: History of Study] , University College London, retrieved 20 September 2007] Production estimates indicate that reef foraminifera annually generate approximately 43 million tons of calcium carbonate and thus play an essential role in the production of reef carbonates.cite journal|title = [http://jfr.geoscienceworld.org/cgi/content/abstract/27/4/271 Global ocean carbonate and carbon dioxide production: The role of reef foraminifera] |year = 1997|last= Langer|first=M. R.|coauthors = Silk, M. T. B., Lipps, J. H.|journal = Journal of Foraminiferal Research|volume = 27|issue = 4|pages = 271–277]

Genetic studies have identified the naked amoeba "Reticulomyxa" and the peculiar xenophyophores as foraminiferans without tests.Fact|date=February 2007 A few other amoeboids produce reticulose pseudopods, and were formerly classified with the forams as the Granuloreticulosa, but this is no longer considered a natural group, and most are now placed among the Cercozoa.cite journal|title = The new higher level classification of Eukaryotes with emphasis on the taxonomy of Protists|year = 2005|last= Adl|first=S. M.|coauthors = Simpson, A. G. B., Farmer, M. A., Anderson, R. A., Anderson, O. R., Barta, J. A., Bowser, S. M., Brugerolle, G., Fensome, R. A., Fredericq, S., James, T. Y., Karpov, S., Kugrens, P., Krug, J., Lane, C. E., Lewis, L. A., Lodge, J., Lynn, D. H., Mann, D. G., McCourt, R. M., Mendoza, L., Moestrup, O., Mozley-Standridge, S. E., Nerad, T. A., Shearer, C. A., Smirnov, A. E., Speigel, F. W., Taylor, M. F. J. R.|journal = Journal of Eukaryotic Microbiology|volume = 52|issue = 5|pages = 399–451|doi = 10.1111/j.1550-7408.2005.00053.x]

Evolutionary significance

Dying planktonic foraminifera continuously rain down on the sea floor in vast numbers, their mineralized tests preserved as fossils in the accumulating sediment. Beginning in the 1960s, and largely under the auspices of the Deep Sea Drilling, Ocean Drilling, and International Ocean Drilling Programmes, as well as for the purposes of oil exploration, advanced deep-sea drilling techniques have been bringing up sediment cores bearing foraminifera fossils by the millions. The effectively unlimited supply of these fossil tests and the relatively high-precision age-control models available for cores has produced an exceptionally high-quality planktonic foraminifera fossil record dating back to the mid-Jurassic, and presents an unparalleled record for scientists testing and documenting the evolutionary process. The exceptional quality of the fossil record has allowed an impressively detailed picture of species inter-relationships to be developed on the basis of fossils, in many cases subsequently validated independently through molecular genetic studies on extant specimens.

Uses of forams

Because of their diversity, abundance, and complex morphology, fossil foraminiferal assemblages are useful for biostratigraphy, and can accurately give relative dates to rocks. The oil industry relies heavily on microfossils such as forams to find potential oil deposits.cite book|title = Fossil Invertebrates|year = 1987|last= Boardman|first=R.S.|publisher= Blackwell|pages = 714]

Calcareous fossil foraminifera are formed from elements found in the ancient seas they lived in. Thus they are very useful in paleoclimatology and paleoceanography. They can be used to reconstruct past climate by examining the stable isotope ratios of oxygen, and the history of the carbon cycle and oceanic productivity by examining the stable isotope ratios of carbon;cite journal|title = Trends, Rhythms, and Aberrations in Global Climate, 65 Ma to Present|year = 2001|last= Zachos|first=J.C.|coauthors = Pagani, M., Sloan, L., Thomas, E., and Billups, K.|journal = Science|volume = 292|pages =686–693|doi = 10.1126/science.1059412|pmid = 11326091] see δ18O and δ13C. Geographic patterns seen in the fossil records of planktonic forams are also used to reconstruct ancient ocean currents.Fact|date=February 2007 Because certain types of foraminifera are found only in certain environments, they can be used to figure out the kind of environment under which ancient marine sediments were deposited.Fact|date=February 2007

For the same reasons they make useful biostratigraphic markers, living foraminiferal assemblages have been used as bioindicators in coastal environments, including indicators of coral reef health.Fact|date=February 2007 Because calcium carbonate is susceptible to dissolution in acidic conditions, foraminifera may be particularly affected by changing climate and ocean acidification.Fact|date=February 2007

Foraminifera can also be utilised in archaeology in the provenancing of some stone raw material types. Some stone types, such as chert, are commonly found to contain fossilised foraminifera. The types and concentrations of these fossils within a sample of stone can be used to match that sample to a source known to contain the same 'fossil signature'.

References

External links

;General information:

* [http://www.ucmp.berkeley.edu/index.html The University of California Museum of Paleontology] website has an [http://www.ucmp.berkeley.edu/foram/foramintro.html Introduction to the Foraminifera]

* Researchers at the University of South Florida developed a system [http://www.marine.usf.edu/reefslab/foramcd/html_files/titlepage.htm using foraminifera for monitoring coral reef environments]

* University College London's [http://www.ucl.ac.uk/GeolSci/micropal/foram.html micropaleontology site] has an overview of foraminifera, including many high-quality SEMs

* [http://paleopolis.rediris.es/cg/CG2006_M02/index.html Illustrated glossary of terms used in foraminiferal research] is the Lukas Hottinger's glossary published in the OA e-journal [http://paleopolis.rediris.es/cg/uk-index.html "Carnets de Géologie - Notebooks on Geology"]

* [http://www.paleontology.uni-bonn.de/frame02.htm Information on Foraminifera] Martin Langer's Micropaleontology Page

* [http://ethomas.web.wesleyan.edu/BFhandout.htm Benthic foraminifera information] from the 2005 Urbino Summer School of Paleoclimatology

;Resources:
* The [http://www.bowserlab.org/starsand.html star*sand project] (part of [http://starcentral.mbl.edu/mv/portal.php?pagetitle=index micro*scope] ) is a cooperative database of information about foraminifera

* [http://webdb2.museum.tohoku.ac.jp/e-foram/ 3D models] of forams, generated by X-ray tomography

* [http://www.chronos.org CHRONOS] has [http://portal.chronos.org/gridsphere/gridsphere?cid=res_foram several foraminifera resources] , including a [http://portal.chronos.org/gridsphere/gridsphere?cid=res_taxondb taxon search page] and a [http://portal.chronos.org/gridsphere/gridsphere?cid=micropaleo micro-paleo section]

* [http://www.eforams.icsr.agh.edu.pl/index.php/Main_Page eForams] is a web site focused on foraminifera and modeling of foraminiferal shells

* [http://www.foraminifera.eu Foraminifera Gallery] Illustrated catalog of recent and fossil Foraminifera by genus and locality