page_title: Foraminifera
section_title: Evolutionary history
hierarchical_section_title: Foraminifera / Evolutionary history
caption_attribution_description: Español: Paleodictyon, probablemente P. imperfectum en arenisca de los flyschs de la punta de San García. Complejos del Campo de Gibraltar, Unidad de Algeciras (Oligoceno-Mioceno). Algeciras, Andalucía, España.
context_page_description: Foraminifera are members of a phylum or class of amoeboid protists characterized by streaming granular ectoplasm for catching food and other uses; and commonly an external shell of diverse forms and materials. Tests of chitin are believed to be the most primitive type. Most foraminifera are marine, the majority of which live on or within the seafloor sediment, while a smaller number float in the water column at various depths. Fewer are known from freshwater or brackish conditions, and some very few soil species have been identified through molecular analysis of small subunit ribosomal DNA.
  Foraminifera typically produce a test, or shell, which can have either one or multiple chambers, some becoming quite elaborate in structure. These shells are commonly made of calcium carbonate or agglutinated sediment particles. Over 50,000 species are recognized, both living and fossil. They are usually less than 1 mm in size, but some are much larger, the largest species reaching up to 20 cm.
  In modern scientific English, the term foraminifera is both singular and plural, and is used to describe one or more specimens or taxa: its usage as singular or plural must be determined from context.
context_section_description: Molecular clocks indicate that the crown-group of foraminifera likely evolved during the Neoproterozoic, between 900 and 650 million years ago; this timing is consistent with Neoproterozoic fossils of the closely related filose amoebae. As fossils of foraminifera have not been found prior to the very end of the Ediacaran, it is likely that most of these Proterozoic forms did not have hard-shelled tests.
  Due to their non-mineralised tests, "allogromiids" have no fossil record. 
  The mysterious vendozoans of the Ediacaran period have been suggested to represent fossil xenophyophores. However, the discovery of diagenetically-altered C₂₇ sterols associated with the remains of Dickinsonia cast doubt on this identification and suggest it may instead be an animal. Other researchers have suggested that the elusive trace fossil Paleodictyon and its relatives may represent a fossil xenophyophore and noted the similarity of the extant xenophyophore Occultammina to the fossil; however, modern examples of Paleodictyon have not been able to clear up the issue and the trace may alternately represent a burrow or a glass sponge. Supporting this notion is the similar habitat of living xenophyophores to the inferred habitat of fossil graphoglyptids; however, the large size and regularity of many graphoglyptids as well as the apparent absence of xenophyae in their fossils casts doubt on the possibility. As of 2017 no definite xenophyophore fossils have been found.
  Test-bearing foraminifera have an excellent fossil record throughout the Phanerozoic eon. The earliest known definite foraminifera appear in the fossil record towards the very end of the Ediacaran; these forms all have agglutinated tests and are unilocular. These include forms like Platysolenites and Spirosolenites.
  Single-chambered foraminifera continued to diversity throughout the Cambrian. Some commonly encountered forms include Ammodiscus, Glomospira,  Psammosphera, and Turritellella; these species are all agglutinated. They make up part of the Ammodiscina, a lineage of spirillinids that still contains modern forms. Later spirillinids would evolve multilocularity and calcitic tests, with the first such forms appearing during the Triassic; the group saw little effects on diversity due to the K-Pg extinction.
  The earliest multi-chambered foraminifera are agglutinated species, and appear in the fossil record during the middle Cambrian period. Due to their poor preservation they cannot be positively assigned to any major foram group.
  The earliest known calcareous-walled foraminifera are the Fusulinids, which appear in the fossil record during the Llandoverian epoch of the early Silurian. The earliest of these were microscopic, planispirally coiled, and evolute; later forms evolved a diversity of shapes including lenticular, globular, and perhaps most famously, elongated rice-shaped forms. Later species of fusulinids grew to much larger size, with some forms reaching 5 cm in length; reportedly, some specimens reach up to 14 cm in length, making them among the largest foraminifera extant or extinct. Fusulinids are the earliest lineage of foraminifera thought to have evolved symbiosis with photosynthetic organisms. Fossils of fusulinids have been found on all continents except Antarctica; they reached their greatest diversity during the Visean epoch of the Carboniferous. The group then gradually declined in diversity until finally going extinct during the Permo-Triassic extinction event.
  During the Tournaisian epoch of the Carboniferous, Miliolid foraminifera first appeared in the fossil record, having diverged from the spirillinids within the Tubothalamea. Miliolids suffered about 50% casualties during both the Permo-Triassic and K-Pg extinctions but survived to the present day. Some fossil miliolids reached up to 2 cm in diameter.
  The earliest known Lagenid fossils appear during the Moscovian epoch of the Carboniferous. Seeing little effect due to the Permo-Triassic or K-Pg extinctions, the group diversified through time. Secondarily unilocular taxa evolved during the Jurassic and C
caption: The mysterious Paleodictyon has been interpreted as a fossil xenophyophore but this remains controversial.
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