Protists in the fossil record

File:Tree of Living Organisms 2.png

{{further|Protista taxonomy}}

Systematists today do not treat Protista as a formal taxon, but the term "protist" is still commonly used for convenience in two ways. The most popular contemporary definition is a phylogenetic one, that identifies a paraphyletic group:{{cite journal | doi=10.1016/j.ode.2006.11.001 | title=Protists – A textbook example for a paraphyletic taxon☆ | journal=Organisms Diversity & Evolution| volume=7 | issue=2 | pages=166–172 | year=2007 | last1=Schlegel | first1=M.| last2=Hulsmann | first2=N.}} a protist is any eukaryote that is not an animal, (land) plant, or (true) fungus; this definition{{cite web | url=http://www.microbeworld.org/types-of-microbes/protista | title=Protista | publisher=microbeworld.org | access-date=11 June 2016 | archive-date=13 June 2016 | archive-url=https://web.archive.org/web/20160613075238/http://www.microbeworld.org/types-of-microbes/protista }} excludes many unicellular groups, like the Microsporidia (fungi), many Chytridiomycetes (fungi), and yeasts (fungi), and also a non-unicellular group included in Protista in the past, the Myxozoa (animal).{{cite journal | vauthors = Štolc A | title = Actinomyxidies, nouveau groupe de Mesozoaires parent des Myxosporidies | year = 1899 | journal = Bull. Int. l'Acad. Sci. Bohème | volume = 12 | pages = 1–12 }}

The other definition describes protists primarily by functional or biological criteria: protists are essentially those eukaryotes that are never multicellular,{{Cite journal | doi = 10.1007/s10539-012-9354-y | title = The other eukaryotes in light of evolutionary protistology | journal = Biology & Philosophy| volume = 28 | issue = 2 | pages = 299–330 | year = 2012 | vauthors = O'Malley MA, Simpson AG, Roger AJ | s2cid = 85406712 }} that either exist as independent cells, or if they occur in colonies, do not show differentiation into tissues (but vegetative cell differentiation may occur restricted to sexual reproduction, alternate vegetative morphology, and quiescent or resistant stages, such as cysts);{{cite journal | vauthors = Adl SM, Simpson AG, Farmer MA, Andersen RA, Anderson OR, Barta JR, Bowser SS, Brugerolle G, Fensome RA, Fredericq S, James TY, Karpov S, Kugrens P, Krug J, Lane CE, Lewis LA, Lodge J, Lynn DH, Mann DG, McCourt RM, Mendoza L, Moestrup O, Mozley-Standridge SE, Nerad TA, Shearer CA, Smirnov AV, Spiegel FW, Taylor MF | title = The new higher level classification of eukaryotes with emphasis on the taxonomy of protists | journal = The Journal of Eukaryotic Microbiology | volume = 52 | issue = 5 | pages = 399–451 | year = 2005 | pmid = 16248873 | doi = 10.1111/j.1550-7408.2005.00053.x | s2cid = 8060916 | doi-access = free }} this definition excludes many brown, multicellular red and green algae, which may have tissues.

The taxonomy of protists is still changing. Newer classifications attempt to present monophyletic groups based on morphological (especially ultrastructural),Pitelka, D. R. (1963). [https://www.biodiversitylibrary.org/bibliography/7050#/summary Electron-Microscopic Structure of Protozoa]. Pergamon Press, Oxford.Berner, T. (1993). [https://books.google.com/books?id=EzDy0Lhes2IC Ultrastructure of Microalgae]. Boca Raton: CRC Press. {{ISBN|0-8493-6323-3}}Beckett, A., Heath, I. B., and Mclaughlin, D. J. (1974). [https://books.google.com/books?id=Qe1IAAAAYAAJ An Atlas of Fungal Ultrastructure.] Longman, Green, New York. biochemical (chemotaxonomy)Ragan M.A. & Chapman D.J. (1978). [https://books.google.com/books?id=BqqnNKmU8I8C A Biochemical Phylogeny of the Protists.] London, New York: Academic Press. {{ISBN|0-323-15561-8}}Lewin R. A. (1974). "Biochemical taxonomy", pp. 1–39 in [https://books.google.com/books?id=tlMSSirdbOkC Algal Physiology and Biochemistry], Stewart W. D. P. (ed.). Blackwell Scientific Publications, Oxford. {{ISBN|0-520-02410-9}} and DNA sequence (molecular research) information.Oren, A., & Papke, R. T. (2010). [https://books.google.com/books?id=a5t9DYZ-wccC Molecular phylogeny of microorganisms]. Norfolk, UK: Caister Academic Press. {{ISBN|1-904455-67-0}}Horner, D. S., & Hirt, R. P. (2004). [https://books.google.com/books?id=KDzfXCptJbQC&lpg=PP1&hl=pt-BR&pg=PA1 "An overview on eukaryote origins and evolution: the beauty of the cell and the fabulous gene phylogenies"], pp. 1–26 in Hirt, R.P. & D.S. Horner. Organelles, Genomes and Eukaryote Phylogeny, An Evolutionary Synthesis in the Age of Genomics. New York: CRC Press. {{ISBN|0-203-50893-9}} However, there are sometimes discordances between molecular and morphological investigations; these can be categorized as two types: (i) one morphology, multiple lineages (e.g. morphological convergence, cryptic species) and (ii) one lineage, multiple morphologies (e.g. phenotypic plasticity, multiple life-cycle stages).{{cite journal | vauthors = Lahr DJ, Laughinghouse HD, Oliverio AM, Gao F, Katz LA | title = How discordant morphological and molecular evolution among microorganisms can revise our notions of biodiversity on Earth | journal = BioEssays | volume = 36 | issue = 10 | pages = 950–959 | date = October 2014 | pmid = 25156897 | pmc = 4288574 | doi = 10.1002/bies.201400056 }}

Because the protists as a whole are paraphyletic, new systems often split up or abandon the kingdom, instead treating the protist groups as separate lines of eukaryotes. The recent scheme by Adl et al. (2005) does not recognize formal ranks (phylum, class, etc.) and instead treats groups as clades of phylogenetically related organisms. This is intended to make the classification more stable in the long term and easier to update. Some of the main groups of protists, which may be treated as phyla, are listed in the taxobox, upper right.{{cite journal | vauthors = Cavalier-Smith T, Chao EE | title = Phylogeny and classification of phylum Cercozoa (Protozoa) | journal = Protist | volume = 154 | issue = 3–4 | pages = 341–358 | date = October 2003 | pmid = 14658494 | doi = 10.1078/143446103322454112 }} Many are thought to be monophyletic, though there is still uncertainty. For instance, the Excavata are probably not monophyletic and the chromalveolates are probably only monophyletic if the haptophytes and cryptomonads are excluded.{{cite journal | vauthors = Parfrey LW, Barbero E, Lasser E, Dunthorn M, Bhattacharya D, Patterson DJ, Katz LA | title = Evaluating support for the current classification of eukaryotic diversity | journal = PLOS Genetics | volume = 2 | issue = 12 | pages = e220 | date = December 2006 | pmid = 17194223 | pmc = 1713255 | doi = 10.1371/journal.pgen.0020220 | doi-access = free }}

(in part)

One of the oldest fossils identified as a red alga is also the oldest fossil eukaryote that belongs to a specific modern taxon. Bangiomorpha pubescens, a multicellular fossil from arctic Canada, strongly resembles the modern red alga Bangia and occurs in rocks dating to 1.05 billion years ago.{{cite journal|last1=Gibson|first1=Timothy M.|last2=Shih|first2=Patrick M.|last3=Cumming|first3=Vivien M.|last4=Fischer|first4=Woodward W.|last5=Crockford|first5=Peter W.|last6=Hodgskiss|first6=Malcolm S.W.|last7=Wörndle|first7=Sarah|last8=Creaser|first8=Robert A.|last9=Rainbird|first9=Robert H.|last10=Skulski|first10=Thomas M.|last11=Halverson|first11=Galen P.|title=Precise age of Bangiomorpha pubescens dates the origin of eukaryotic photosynthesis|journal=Geology|volume=46|issue=2|year=2017|pages=135–138|issn=0091-7613|doi=10.1130/G39829.1|bibcode=2018Geo....46..135G |url=https://authors.library.caltech.edu/83811/3/2018030.pdf}}

Two kinds of fossils resembling red algae were found sometime between 2006 and 2011 in well-preserved sedimentary rocks in Chitrakoot, central India. The presumed red algae lie embedded in fossil mats of cyanobacteria, called stromatolites, in 1.6 billion-year-old Indian phosphorite – making them the oldest plant-like fossils ever found by about 400 million years.{{cite journal|last1=Bengtson|first1=S|last2=Sallstedt|first2=T|last3=Belivanova|first3=V|last4=Whitehouse|first4=M|date=2017|title=Three-dimensional preservation of cellular and subcellular structures suggests 1.6 billion-year-old crown-group red algae|journal=PLOS Biol|volume=15|issue=3|doi=10.1371/journal.pbio.2000735|page=e2000735|pmid=28291791|pmc=5349422|doi-access=free}}

Red algae are important builders of limestone reefs. The earliest such coralline algae, the solenopores, are known from the Cambrian period. Other algae of different origins filled a similar role in the late Paleozoic, and in more recent reefs.

Calcite crusts that have been interpreted as the remains of coralline red algae, date to the Ediacaran Period.{{Cite journal

|author1=Grant, S. W. F. |author2=Knoll, A. H. |author3=Germs, G. J. B. | year = 1991

| title = Probable Calcified Metaphytes in the Latest Proterozoic Nama Group, Namibia: Origin, Diagenesis, and Implications

| journal = Journal of Paleontology

| volume = 65

| issue = 1

| pages = 1–18

| pmid = 11538648

| jstor=1305691

|doi=10.1017/S002233600002014X |bibcode=1991JPal...65....1G |s2cid=26792772 }} Thallophytes resembling coralline red algae are known from the late Proterozoic Doushantuo formation.{{Cite journal

|author1=Yun, Z. |author2=Xun-lal, Y. | year = 1992

| title = New data on multicellular thallophytes and fragments of cellular tissues from Late Proterozoic phosphate rocks, South China

| journal = Lethaia

| volume = 25

| issue = 1

| pages = 1–18

| doi = 10.1111/j.1502-3931.1992.tb01788.x

}}

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The occurrence of Phaeophyceae as fossils is rare due to their generally soft-bodied nature,

{{cite book|last=Arnold |first=C. A.|year=1947|title=An Introduction to Paleobotany|url=https://archive.org/details/in.ernet.dli.2015.50241 |page=[https://archive.org/details/in.ernet.dli.2015.50241/page/n64 48]|location=New York; London|publisher=McGraw-Hill|isbn=978-1-4067-1861-4}} and scientists continue to debate the identification of some finds.

{{cite journal|last1=Coyer |first1=J. A.|last2=Smith |first2=G. J.|last3=Andersen |first3=R. A.|year=2001|title=Evolution of Macrocystis spp. (Phaeophyta) as determined by ITS1 and ITS2 sequences|url=http://129.125.2.51/fmns-research/marbee/publications/CoyerJPhyc01.pdf|journal=Journal of Phycology|volume=37|issue=4|pages=574–585|doi=10.1046/j.1529-8817.2001.037001574.x|s2cid=84074495 }} Part of the problem with identification lies in the convergent evolution of morphologies between many brown and red algae.

{{cite journal|last1=Fry |first1=W. L.|last2=Banks |first2=H. P.|year=1955|title=Three new genera of algae from the Upper Devonian of New York|journal=Journal of Paleontology|volume=29 |issue=1|pages=37–44|jstor=1300127}} Most fossils of soft-tissue algae preserve only a flattened outline, without the microscopic features that permit the major groups of multicellular algae to be reliably distinguished. Among the brown algae, only species of the genus Padina deposit significant quantities of minerals in or around their cell walls.

{{cite book|last=Prescott |first=G. W.|year=1968|title=The Algae: A Review|url=https://archive.org/details/algaereview0000pres |url-access=registration |pages=[https://archive.org/details/algaereview0000pres/page/207 207]–231, 371–372|location=Boston|publisher=Houghton Mifflin Company|isbn=978-3-87429-244-3}} Other algal groups, such as the red algae and green algae, have a number of calcareous members. Because of this, they are more likely to leave evidence in the fossil record than the soft bodies of most brown algae and more often can be precisely classified.

{{cite book|last=Simpson |first=G. G.|year=1953|title=Life of the Past: An Introduction to Paleontology|url=https://archive.org/details/lifeofpastintr00simp |url-access=registration |pages=[https://archive.org/details/lifeofpastintr00simp/page/158 158–159]|location=New Haven|publisher=Yale University Press}}

Fossils comparable in morphology to brown algae are known from strata as old as the Upper Ordovician,

{{cite journal|last=Fry |first=W. L.|year=1983|title=An algal flora from the Upper Ordovician of the Lake Winnipeg region, Manitoba, Canada|journal=Review of Palaeobotany and Palynology|volume=39 |issue=3–4 |pages=313–341|doi=10.1016/0034-6667(83)90018-0|bibcode=1983RPaPa..39..313F }} but the taxonomic affinity of these impression fossils is far from certain.

{{cite web|last1=Speer |first1=B. R.|last2=Waggoner |first2=B. M.|year=2000|title=Phaeophyta: Fossil Record|url=http://www.ucmp.berkeley.edu/chromista/browns/phaeofr.html}} Claims that earlier Ediacaran fossils are brown algae

{{Cite journal|last=Loeblich |first=A. R.|year=1974|title=Protistan Phylogeny as Indicated by the Fossil Record|journal=Taxon|volume=23 |issue=2/3 |pages=277–290|doi=10.2307/1218707|jstor=1218707 }} have since been dismissed.

{{Cite book|last=Lee|first=R. E.|year= 2008|title=Phycology|edition=4th|publisher= Cambridge University Press|isbn= 978-0-521-63883-8|url-access=registration|url= https://archive.org/details/phycology00robe}} While many carbonaceous fossils have been described from the Precambrian, they are typically preserved as flattened outlines or fragments measuring only millimeters long.

{{cite book|last=Hofmann |first=H. J.|year=1985|chapter=Precambrian Carbonaceous Megafossils|editor=D. F. Toomey |editor2=M. H. Nitecki|title=Paleoalgology: Contemporary Research and Applications|pages=20–33|location=Berlin|publisher=Springer-Verlag}} Because these fossils lack features diagnostic for identification at even the highest level, they are assigned to fossil form taxa according to their shape and other gross morphological features.

{{cite book|last=Hofmann |first=H. J.|year=1994|chapter=Proterozoic carbonaceous compressions ("metaphytes" and "worms")|editor-last=Bengtson |editor-first=S.|title=Life on Earth|pages=342–357|series=Nobel Symposium|volume=84|location=New York|publisher=Columbia University Press}} A number of Devonian fossils termed fucoids, from their resemblance in outline to species in the genus Fucus, have proven to be inorganic rather than true fossils. The Devonian megafossil Prototaxites, which consists of masses of filaments grouped into trunk-like axes, has been considered a possible brown alga.

{{cite book|last1=Bold |first1=H. C.|last2=Alexopoulos |first2=C. J.|last3=Delevoryas |first3=T.|year=1987|title=Morphology of Plants and Fungi|edition=5th |pages=112–131, 174–186|location=New York|publisher=Harper & Row Publishers|isbn=978-0-06-040839-8

}} However, modern research favors reinterpretation of this fossil as a terrestrial fungus or fungal-like organism.

{{cite journal|last1=Hueber |first1=F. M.|year=2001|title=Rotted wood-alga-fungus: the history and life of Prototaxites Dawson 1859|journal=Review of Palaeobotany and Palynology|volume=116 |issue=1 |pages=123–158|doi=10.1016/S0034-6667(01)00058-6

|bibcode=2001RPaPa.116..123H }} Likewise, the fossil Protosalvinia was once considered a possible brown alga, but is now thought to be an early land plant.

{{cite journal |last1 = Taylor |first1 = W. A. |last2 = Taylor |first2 = T. N. |year = 1987 |title = Spore wall ultrastructure of Protosalvinia |url = http://paleobotany.bio.ku.edu/taylorPDFs%5C%5B1987%5D%20Taylor%20and%20Taylor-Spore%20wall%20ultrastructure%20of%20Protosalvinia.pdf|journal = American Journal of Botany |volume = 74 |issue = 3 |pages = 437–443 |doi = 10.2307/2443819 |jstor = 2443819 |archive-url = https://web.archive.org/web/20100617124912/http://paleobotany.bio.ku.edu/taylorPDFs/%5B1987%5D%20Taylor%20and%20Taylor-Spore%20wall%20ultrastructure%20of%20Protosalvinia.pdf |archive-date = 2010-06-17}}

A number of Paleozoic fossils have been tentatively classified with the brown algae, although most have also been compared to known red algae species. Phascolophyllaphycus possesses numerous elongate, inflated blades attached to a stipe. It is the most abundant of algal fossils found in a collection made from Carboniferous strata in Illinois.

{{cite journal|last=Leary |first=R. L.|year=1986|title=Three new genera of fossil noncalcareous algae from Valmeyeran (Mississippian) strata of Illinois|journal=American Journal of Botany|volume=73 |issue=3 |pages=369–375|doi=10.2307/2444080|jstor=2444080}} Each hollow blade bears up to eight pneumatocysts at its base, and the stipes appear to have been hollow and inflated as well. This combination of characteristics is similar to certain modern genera in the order Laminariales (kelps). Several fossils of Drydenia and a single specimen of Hungerfordia from the Upper Devonian of New York have also been compared to both brown and red algae. Fossils of Drydenia consist of an elliptical blade attached to a branching filamentous holdfast, not unlike some species of Laminaria, Porphyra, or Gigartina. The single known specimen of Hungerfordia branches dichotomously into lobes and resembles genera like Chondrus and Fucus or Dictyota.

{{cite book|last1=Bold|first1=H. C.|last2=Wynne|first2=M. J.|year=1978|title=Introduction to the Algae|edition=2nd|page=[https://archive.org/details/introductiontoal0000bold/page/27 27]|publisher=Prentice-Hall|isbn=978-0-13-477786-3|url-access=registration|url=https://archive.org/details/introductiontoal0000bold/page/27}}

The earliest known fossils that can be assigned reliably to the Phaeophyceae come from Miocene diatomite deposits of the Monterey Formation in California.{{cite book|title=Algae: An Introduction to Phycology|last1=van den Hoek|first1=C.|last2=Mann|first2=D. G.|last3=Jahns|first3=H. M.|publisher=Cambridge University Press|year=1995|isbn=978-0-521-31687-3|location=Cambridge|pages=165–218}} Several soft-bodied brown macroalgae, such as Julescraneia, have been found.

{{cite journal

|last1=Parker |first1=B. C.

|last2=Dawson |first2=E. Y.

|year=1965

|title=Non-calcareous marine algae from California Miocene deposits

|journal=Nova Hedwigia

|volume=10 |pages=273–295; plates 76–96

}}

Heterokont chloroplasts appear to derive from those of red algae, rather than directly from prokaryotes as occurred in plants. This suggests they had a more recent origin than many other algae. However, fossil evidence is scant, and only with the evolution of the diatoms themselves do the heterokonts make a serious impression on the fossil record.

The earliest known fossil diatoms date from the early Jurassic (~185 Ma ago),{{cite journal |doi=10.1006/mpev.1996.0088 |pmid=8975694 |title=Evolution of the Diatoms (Bacillariophyta) |journal=Molecular Phylogenetics and Evolution |volume=6 |issue=3 |pages=391–407 |year=1996 |last1=Kooistra |first1=Wiebe H.C.F. |last2=Medlin |first2=Linda K. }} although the molecular clock and sedimentary{{cite journal |doi=10.1038/35023143 |pmid=10984049 |year=2000 |last1=Schieber |first1=Jürgen |title=Diagenetic origin of quartz silt in mudstones and implications for silica cycling |journal=Nature |volume=406 |issue=6799 |pages=981–5 |last2=Krinsley |first2=Dave |last3=Riciputi |first3=Lee |bibcode=2000Natur.406..981S |s2cid=4417951 }} evidence suggests an earlier origin. It has been suggested that their origin may be related to the end-Permian mass extinction (~250 Ma), after which many marine niches were opened.{{cite journal |hdl=10013/epic.12689| last1 = Medlin | first1 = L. K. | last2 = Kooistra | first2 = W. H. C. F. | last3 = Gersonde | first3 = R. | last4 = Sims | first4 = P. A. | last5 = Wellbrock | first5 = U. | year = 1997 | title = Is the origin of the diatoms related to the end-Permian mass extinction? | journal = Nova Hedwigia | volume = 65 | issue = 1–4 | pages = 1–11 | doi = 10.1127/nova.hedwigia/65/1997/1 }} The gap between this event and the time that fossil diatoms first appear may indicate a period when diatoms were unsilicified and their evolution was cryptic.{{cite journal |doi=10.1111/j.1469-8137.2004.01022.x |jstor=1514475 |title=The evolution of silicification in diatoms: Inescapable sinking and sinking as escape? |journal=New Phytologist |volume=162 |issue=1 |pages=45–61 |year=2004 |last1=Raven |first1=J. A. |last2=Waite |first2=A. M. |doi-access=free }} Since the advent of silicification, diatoms have made a significant impression on the fossil record, with major fossil deposits found as far back as the early Cretaceous, and with some rocks such as diatomaceous earth, being composed almost entirely of them.

Although diatoms may have existed since the Triassic, the timing of their ascendancy and "take-over" of the silicon cycle occurred more recently. Prior to the Phanerozoic (before 544 Ma), it is believed that microbial or inorganic processes weakly regulated the ocean's silicon cycle.{{cite book|author1= R. Siever|author2= Stephen Henry Schneider|author3= Penelope J. Boston|title= Scientists on Gaia|chapter-url= https://books.google.com/books?id=h83nGwAACAAJ|access-date= 14 November 2013|date= January 1993|publisher= MIT Press|isbn= 978-0-262-69160-4|pages= [https://archive.org/details/scientistsongaia0000unse/page/287 287–295]|chapter= Silica in the oceans: biological-geological interplay|url-access= registration|url= https://archive.org/details/scientistsongaia0000unse/page/287}}{{cite journal |doi=10.1086/320794 |title=Secular Distribution of Biogenic Silica through the Phanerozoic: Comparison of Silica-Replaced Fossils and Bedded Cherts at the Series Level |journal=The Journal of Geology |volume=109 |issue=4 |pages=509–22 |year=2001 |last1=Kidder |first1=David L. |last2=Erwin |first2=Douglas H. |bibcode=2001JG....109..509K |s2cid=128401816 }}{{cite journal |doi=10.1130/0091-7613(2003)031<0319:PAMSRS>2.0.CO;2 |id={{INIST|14692468}} |year=2003 |volume=31 |issue=4 |pages=319–22 |title=Paleozoic and Mesozoic silica-rich seawater: Evidence from hematitic chert (jasper) deposits |journal=Geology |last1=Grenne |first1=Tor |last2=Slack |first2=John F. |bibcode=2003Geo....31..319G }} Subsequently, the cycle appears dominated (and more strongly regulated) by the radiolarians and siliceous sponges, the former as zooplankton, the latter as sedentary filter-feeders primarily on the continental shelves.{{cite journal |doi=10.1016/S0012-8252(00)00024-6 |title=Radiolarian palaeoecology and radiolarites: Is the present the key to the past? |journal=Earth-Science Reviews |volume=52 |issue=1 |pages=83–120 |year=2000 |last1=Racki |first1=G |last2=Cordey |first2=Fabrice |bibcode=2000ESRv...52...83R }} Within the last 100 My, it is thought that the silicon cycle has come under even tighter control, and that this derives from the ecological ascendancy of the diatoms.

However, the precise timing of the "take-over" remains unclear, and different authors have conflicting interpretations of the fossil record. Some evidence, such as the displacement of siliceous sponges from the shelves,{{cite journal |doi=10.1038/44560 |id={{INIST|1990263}} |year=1999 |last1=Maldonado |first1=Manuel |title=Decline in Mesozoic reef-building sponges explained by silicon limitation |journal=Nature |volume=401 |issue=6755 |pages=785–8 |last2=Carmona |first2=M. Carmen |last3=Uriz |first3=María J. |last4=Cruzado |first4=Antonio |bibcode=1999Natur.401..785M |s2cid=205034177 }} suggests that this takeover began in the Cretaceous (146 Ma to 66 Ma), while evidence from radiolarians suggests "take-over" did not begin until the Cenozoic (66 Ma to present).{{cite journal |doi=10.1130/0091-7613(1975)3<175:SDACRE>2.0.CO;2 |year=1975 |volume=3 |issue=4 |pages=175–7 |title=Silica, diatoms, and Cenozoic radiolarian evolution |journal=Geology |last1=Harper |first1=Howard E. |last2=Knoll |first2=Andrew H. |bibcode=1975Geo.....3..175H }}

The expansion of grassland biomes and the evolutionary radiation of grasses during the Miocene is believed to have increased the flux of soluble silicon to the oceans, and it has been argued that this promoted the diatoms during the Cenozoic era.{{cite journal |doi=10.1126/science.1095964 |pmid=15256663 |title=The Evolution of Modern Eukaryotic Phytoplankton |journal=Science |volume=305 |issue=5682 |pages=354–60 |year=2004 |last1=Falkowski |first1=P. G. |last2=Katz |first2=Miriam E. |last3=Knoll |first3=Andrew H. |last4=Quigg |first4=Antonietta |last5=Raven |first5=John A. |last6=Schofield |first6=Oscar |last7=Taylor |first7=F. J. R. |bibcode=2004Sci...305..354F |citeseerx=10.1.1.598.7930 |s2cid=451773 }}{{cite journal |doi=10.2110/palo.2003.p03-108 |jstor=27670327 |title=Impact of Grassland Radiation on the Nonmarine Silica Cycle and Miocene Diatomite |journal=PALAIOS |volume=20 |issue=2 |pages=198–206 |year=2005 |last1=Kidder |first1=D. L. |last2=Gierlowski-Kordesch |first2=E. H. |bibcode=2005Palai..20..198K |s2cid=140584104 }} Recent work suggests that diatom success is decoupled from the evolution of grasses, although both diatom and grassland diversity increased strongly from the middle Miocene.{{cite journal |doi=10.1371/journal.pone.0084857 |pmid=24465441 |pmc=3898954 |title=Cenozoic Planktonic Marine Diatom Diversity and Correlation to Climate Change |journal=PLOS ONE |volume=9 |issue=1 |pages=e84857 |year=2014 |last1=Lazarus |first1=David |last2=Barron |first2=John |last3=Renaudie |first3=Johan |last4=Diver |first4=Patrick |last5=Türke |first5=Andreas |bibcode=2014PLoSO...984857L |doi-access=free }}

Diatom diversity over the Cenozoic has been very sensitive to global temperature, particularly to the equator-pole temperature gradient. Warmer oceans, particularly warmer polar regions, have in the past been shown to have had substantially lower diatom diversity. Future warm oceans with enhanced polar warming, as projected in global-warming scenarios,IPCC Core Writing Team, 2007. Climate Change 2007: Synthesis Report. 104. could thus in theory result in a significant loss of diatom diversity, although from current knowledge it is impossible to say if this would occur rapidly or only over many tens of thousands of years.

The fossil record of diatoms has largely been established through the recovery of their siliceous frustules in marine and non-marine sediments. Although diatoms have both a marine and non-marine stratigraphic record, diatom biostratigraphy, which is based on time-constrained evolutionary originations and extinctions of unique taxa, is only well developed and widely applicable in marine systems. The duration of diatom species ranges have been documented through the study of ocean cores and rock sequences exposed on land.{{cite journal |last1=Scherer |first1=R. P. |last2=Gladenkov |first2=A. Yu. |last3=Barron |first3=J. A. |year=2007 |title=Methods and applications of Cenozoic marine diatom biostratigraphy |journal=Paleontological Society Papers |volume=13 |pages=61–83 |doi=10.1017/S1089332600001467 }} Where diatom biozones are well established and calibrated to the geomagnetic polarity time scale (e.g., Southern Ocean, North Pacific, eastern equatorial Pacific), diatom-based age estimates may be resolved to within <100,000 years, although typical age resolution for Cenozoic diatom assemblages is several hundred thousand years.

Diatoms preserved in lake sediments are widely used for paleoenvironmental reconstructions of Quaternary climate, especially for closed-basin lakes which experience fluctuations in water depth and salinity.

The Cretaceous record of diatoms is limited, but recent studies reveal a progressive diversification of diatom types. The Cretaceous–Paleogene extinction event, which in the oceans dramatically affected organisms with calcareous skeletons, appears to have had relatively little impact on diatom evolution.{{cite journal |last1=Harwood |first1=D. M. |last2=Nikolaev |first2=V. A. |last3=Winter |first3=D. M. |year=2007 |title=Cretaceous record of diatom evolution, radiation, and expansion |journal=Paleontological Society Papers |volume=13 |pages=33–59 |doi=10.1017/S1089332600001455 }}

Although no mass extinctions of marine diatoms have been observed during the Cenozoic, times of relatively rapid evolutionary turnover in marine diatom species assemblages occurred near the Paleocene–Eocene boundary,{{cite book |last=Strelnikova |first=N. I. |year=1990 |chapter=Evolution of diatoms during the Cretaceous and Paleogene periods |editor-last=Simola |editor-first=H. |title=Proceedings of the Tenth International Diatom Symposium |publisher=Koeltz Scientific Books |location=Koenigstein |pages=195–204 |isbn=3-87429-307-6 }} and at the Eocene–Oligocene boundary.{{cite book |last=Baldauf |first=J. G. |year=1993 |contribution=Middle Eocene through early Miocene diatom floral turnover |editor-last=Prothero |editor-first=D. |editor2-last=Berggren |editor2-first=W. H. |title=Eocene-Oligocene climatic and biotic evolution |publisher=Princeton University Press |location=Princeton |pages=310–326 |isbn=0-691-02542-8 }} Further turnover of assemblages took place at various times between the middle Miocene and late Pliocene,{{cite journal |last=Barron |first=J. A. |year=2003 |title=Appearance and extinction of planktonic diatoms during the past 18 m.y. in the Pacific and Southern oceans |journal=Diatom Research |volume=18 |pages=203–224 |doi=10.1080/0269249x.2003.9705588 |s2cid=84781882 }} in response to progressive cooling of polar regions and the development of more endemic diatom assemblages.

A global trend toward more delicate diatom frustules has been noted from the Oligocene to the Quaternary. This coincides with an increasingly more vigorous circulation of the ocean's surface and deep waters brought about by increasing latitudinal thermal gradients at the onset of major ice sheet expansion on Antarctica and progressive cooling through the Neogene and Quaternary towards a bipolar glaciated world. This caused diatoms to take in less silica for the formation of their frustules. Increased mixing of the oceans renews silica and other nutrients necessary for diatom growth in surface waters, especially in regions of coastal and oceanic upwelling.

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Dinoflagellates are mainly represented as fossils by fossil dinocysts, which have a long geological record with lowest occurrences during the mid-Triassic,{{cite journal |vauthors=MacRae RA, Fensome RA, Williams GL |title=Fossil dinoflagellate diversity, originations, and extinctions and their significance |journal=Can. J. Bot. |volume=74 |issue= 11|pages=1687–94 |year=1996 |issn=0008-4026 |doi=10.1139/b96-205 }} whilst geochemical markers suggest a presence to the Early Cambrian.{{cite journal | vauthors = Moldowan JM, Talyzina NM | title = Biogeochemical evidence for dinoflagellate ancestors in the Early Cambrian | journal = Science | volume = 281 | issue = 5380 | pages = 1168–70 | date = August 1998 | pmid = 9712575 | doi = 10.1126/science.281.5380.1168 | bibcode = 1998Sci...281.1168M }}

Some evidence indicates dinosteroids in many Paleozoic and Precambrian rocks might be the product of ancestral dinoflagellates (protodinoflagellates).{{cite journal |vauthors=Moldowan JM, Dahl JE, Jacobson SR, Huizinga BJ, Fago FJ, Shetty R, Watt DS, Peters KE |title=Chemostratigraphic reconstruction of biofacies: molecular evidence linking cyst-forming dinoflagellates with Pre-Triassic ancestors |journal=Geology |volume=24 |issue=2 |pages=159–162 |date=February 1996 |doi=10.1130/0091-7613(1996)024<0159:CROBME>2.3.CO;2 |bibcode=1996Geo....24..159M }}{{cite journal |vauthors=Talyzina NM, Moldowan JM, Johannisson A, Fago FJ |title=Affinities of early Cambrian acritarchs studied by using microscopy, fluorescence flow cytometry and biomarkers |journal=Rev. Palaeobot. Palynol. |volume=108 |issue=1–2 |pages=37–53 |date=January 2000 |doi=10.1016/S0034-6667(99)00032-9 |bibcode=2000RPaPa.108...37T }}

Molecular phylogenetics show that dinoflagellates are grouped with ciliates and apicomplexans (=Sporozoa) in a well-supported clade, the alveolates. The closest relatives to dinokaryotic dinoflagellates appear to be apicomplexans, Perkinsus, Parvilucifera, syndinians, and Oxyrrhis.{{cite journal |author1=Saldarriaga J |author2=Taylor MFJR |author3=Cavalier-Smith T |author4=Menden-Deuer S |author4-link=Susanne Menden-Deuer|author5=Keeling PJ |title=Molecular data and the evolutionary history of dinoflagellates |journal=Eur J Protistol |volume=40 |issue=1 |pages=85–111 |year=2004 |doi=10.1016/j.ejop.2003.11.003 |hdl=2429/16056 |hdl-access=free }} Molecular phylogenies are similar to phylogenies based on morphology.{{cite journal |vauthors=Fensome RA, Saldarriaga JF, Taylor FJ |title=Dinoflagellate phylogeny revisited: reconciling morphological and molecular based phylogenies |journal=Grana |volume=38 |issue=2–3 |pages=66–80 |year=1999 |doi=10.1080/00173139908559216 |doi-access=free }}

The earliest stages of dinoflagellate evolution appear to be dominated by parasitic lineages, such as perkinsids and syndinians (e.g. Amoebophrya and Hematodinium).{{cite journal | vauthors = Gunderson JH, Goss SH, Coats DW | title = The phylogenetic position of Amoebophrya sp. infecting Gymnodinium sanguineum | journal = The Journal of Eukaryotic Microbiology | volume = 46 | issue = 2 | pages = 194–7 | year = 1999 | pmid = 10361739 | doi = 10.1111/j.1550-7408.1999.tb04603.x | s2cid = 7836479 }}
{{cite journal | vauthors = Gunderson JH, John SA, Boman WC, Coats DW | title = Multiple strains of the parasitic dinoflagellate Amoebophrya exist in Chesapeake Bay | journal = The Journal of Eukaryotic Microbiology | volume = 49 | issue = 6 | pages = 469–74 | year = 2002 | pmid = 12503682 | doi = 10.1111/j.1550-7408.2002.tb00230.x | s2cid = 30051291 }}{{cite journal | vauthors = López-García P, Rodríguez-Valera F, Pedrós-Alió C, Moreira D | title = Unexpected diversity of small eukaryotes in deep-sea Antarctic plankton | journal = Nature | volume = 409 | issue = 6820 | pages = 603–7 | date = February 2001 | pmid = 11214316 | doi = 10.1038/35054537 | bibcode = 2001Natur.409..603L | s2cid = 11550698 }}{{cite journal | vauthors = Moon-van der Staay SY, De Wachter R, Vaulot D | title = Oceanic 18S rDNA sequences from picoplankton reveal unsuspected eukaryotic diversity | journal = Nature | volume = 409 | issue = 6820 | pages = 607–10 | date = February 2001 | pmid = 11214317 | doi = 10.1038/35054541 | bibcode = 2001Natur.409..607M | s2cid = 4362835 }}{{cite journal | vauthors = Saldarriaga JF, Taylor FJ, Keeling PJ, Cavalier-Smith T | title = Dinoflagellate nuclear SSU rRNA phylogeny suggests multiple plastid losses and replacements | journal = Journal of Molecular Evolution | volume = 53 | issue = 3 | pages = 204–13 | date = September 2001 | pmid = 11523007 | doi = 10.1007/s002390010210 | bibcode = 2001JMolE..53..204S | s2cid = 28522930 }}

All dinoflagellates contain red algal plastids or remnant (nonphotosynthetic) organelles of red algal origin.{{cite journal | vauthors = Janouskovec J, Horák A, Oborník M, Lukes J, Keeling PJ | title = A common red algal origin of the apicomplexan, dinoflagellate, and heterokont plastids | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 107 | issue = 24 | pages = 10949–54 | date = June 2010 | pmid = 20534454 | pmc = 2890776 | doi = 10.1073/pnas.1003335107 | bibcode = 2010PNAS..10710949J | doi-access = free }} The parasitic dinoflagellate Hematodinium however lacks a plastid entirely.{{cite journal | vauthors = Gornik SG, Cassin AM, MacRae JI, Ramaprasad A, Rchiad Z, McConville MJ, Bacic A, McFadden GI, Pain A, Waller RF | title = Endosymbiosis undone by stepwise elimination of the plastid in a parasitic dinoflagellate | journal = Proceedings of the National Academy of Sciences of the United States of America | volume = 112 | issue = 18 | pages = 5767–72 | date = May 2015 | pmid = 25902514 | pmc = 4426444 | doi = 10.1073/pnas.1423400112 | bibcode = 2015PNAS..112.5767G | doi-access = free }} Some groups that have lost the photosynthetic properties of their original red algae plastids has obtained new photosynthetic plastids (chloroplasts) through so-called serial endosymbiosis, both secondary and tertiary. Like their original plastids, the new chloroplasts in these groups can be traced back to red algae, except from those in the members of the genus Lepidodinium, which possess plastids derived from green algae, possibly Trebouxiophyceae or Ulvophyceae.{{Cite journal |pmc = 4547248|year = 2015|last1 = Dorrell|first1 = R. G.|title = Integration of plastids with their hosts: Lessons learned from dinoflagellates|journal = Proceedings of the National Academy of Sciences of the United States of America|volume = 112|issue = 33|pages = 10247–10254|last2 = Howe|first2 = C. J.|pmid = 25995366|doi = 10.1073/pnas.1421380112|bibcode = 2015PNAS..11210247D|doi-access = free}}{{Cite thesis |degree=Master's |hdl=10852/11559 |title=Investigating the plastid replacement in the green dinoflagellate Lepidodinium chlorophorum |date=2010 |last1=Tørresen |first1=Ole Kristian |publisher=University of Oslo}} Lineages with tertiary endosymbiosis are Dinophysis, with plastids from a cryptomonad,{{cite journal|url=https://www.researchgate.net/publication/221990378|title=The toxic dinoflagellate Dinophysis acuminata harbors permanent chloroplasts of cryptomonad origin, not kleptochloroplasts|date=January 2010|journal=Harmful Algae|volume=8|issue=1|pages=25–38|doi=10.1016/j.hal.2009.07.002|author1=Lydia Garcia-Cuetos|author2=Per Juel Hansen|author3=Niels Daugbjerg}} the Karenia, Karlodinium, and Takayama, which possess plastids of haptophyte origin, and the Peridiniaceae, Durinskia and Kryptoperidinium, which has plastids derived from diatoms{{Cite journal|pmc=5888634|year=2018|last1=Klinger|first1=C. M.|title=Plastid Transcript Editing across Dinoflagellate Lineages Shows Lineage-Specific Application but Conserved Trends|journal=Genome Biology and Evolution|volume=10|issue=4|pages=1019–1038|last2=Paoli|first2=L.|last3=Newby|first3=R. J.|last4=Wang|first4=M. Y.|last5=Carroll|first5=H. D.|last6=Leblond|first6=J. D.|last7=Howe|first7=C. J.|last8=Dacks|first8=J. B.|last9=Bowler|first9=C.|last10=Cahoon|first10=A. B.|last11=Dorrell|first11=R. G.|last12=Richardson|first12=E.|pmid=29617800|doi=10.1093/gbe/evy057}}{{Cite journal|pmc=2096628|year=2007|last1=Imanian|first1=B.|title=The dinoflagellates Durinskia baltica and Kryptoperidinium foliaceum retain functionally overlapping mitochondria from two evolutionarily distinct lineages|journal=BMC Evolutionary Biology|volume=7|pages=172|last2=Keeling|first2=P. J.|pmid=17892581|doi=10.1186/1471-2148-7-172 |doi-access=free }} Some species also perform kleptoplasty.{{Cite journal |pmid = 17227410|year = 2007|last1 = Gast|first1 = R. J.|title = Kleptoplasty in an Antarctic dinoflagellate: Caught in evolutionary transition?|journal = Environmental Microbiology|volume = 9|issue = 1|pages = 39–45|last2 = Moran|first2 = D. M.|last3 = Dennett|first3 = M. R.|last4 = Caron|first4 = D. A.|doi = 10.1111/j.1462-2920.2006.01109.x}}

Dinoflagellate evolution has been summarized into five principal organizational types: prorocentroid, dinophysoid, gonyaulacoid, peridinioid, and gymnodinoid.{{cite journal | vauthors = Taylor FJ | title = On dinoflagellate evolution | journal = Bio Systems | volume = 13 | issue = 1–2 | pages = 65–108 | year = 1980 | pmid = 7002229 | doi = 10.1016/0303-2647(80)90006-4 }}

The transitions of marine species into fresh water have been infrequent events during the diversification of dinoflagellates and in most cases have not occurred recently, possibly as late as the Cretaceous.{{cite journal | vauthors = Logares R, Shalchian-Tabrizi K, Boltovskoy A, Rengefors K | title = Extensive dinoflagellate phylogenies indicate infrequent marine-freshwater transitions | journal = Molecular Phylogenetics and Evolution | volume = 45 | issue = 3 | pages = 887–903 | date = December 2007 | pmid = 17928239 | doi = 10.1016/j.ympev.2007.08.005 }}

Recently, the "living fossil" Dapsilidinium pastielsii was found inhabiting the Indo-Pacific Warm Pool, which served as a refugium for thermophilic dinoflagellates.{{cite journal |vauthors=Mertens KN, Takano Y, Head MJ, Matsuoka K |title=Living fossils in the Indo-Pacific warm pool: A refuge for thermophilic dinoflagellates during glaciations |journal=Geology |volume= 42|issue= 6|pages= 531–534|year=2014 |doi=10.1130/G35456.1 |bibcode=2014Geo....42..531M }}

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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.{{Cite journal|last1=Pawlowski|first1=Jan|last2=Holzmann|first2=Maria|last3=Berney|first3=Cédric|last4=Fahrni|first4=José|last5=Gooday|first5=Andrew J.|last6=Cedhagen|first6=Tomas|last7=Habura|first7=Andrea|last8=Bowser|first8=Samuel S.|date=2003-09-30|title=The evolution of early Foraminifera|journal=Proceedings of the National Academy of Sciences|language=en|volume=100|issue=20|pages=11494–11498|doi=10.1073/pnas.2035132100|issn=0027-8424|pmid=14504394|pmc=208786|bibcode=2003PNAS..10011494P|doi-access=free}}{{Cite journal|last1=Groussin|first1=Mathieu|last2=Pawlowski|first2=Jan|last3=Yang|first3=Ziheng|date=2011-10-01|title=Bayesian relaxed clock estimation of divergence times in foraminifera|url=http://www.sciencedirect.com/science/article/pii/S1055790311002752|journal=Molecular Phylogenetics and Evolution|language=en|volume=61|issue=1|pages=157–166|doi=10.1016/j.ympev.2011.06.008|pmid=21723398|issn=1055-7903|url-access=subscription}}

File:Paleodictyon P.San García Algeciras I03.JPG has been interpreted as a fossil xenophyophore but this remains controversial.]]

File:Fusulinid cutaway.gif]]

File:Foraminifera hg.jpgn foraminifera]]

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.{{Cite journal|last=Seilacher|first=A.|s2cid=128619251|date=2007-01-01|title=The nature of vendobionts|url=https://sp.lyellcollection.org/content/286/1/387|journal=Geological Society, London, Special Publications|language=en|volume=286|issue=1|pages=387–397|doi=10.1144/SP286.28|bibcode=2007GSLSP.286..387S|issn=0305-8719|url-access=subscription}} 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.{{Cite journal|last1=Bobrovskiy|first1=Ilya|last2=Hope|first2=Janet M.|last3=Ivantsov|first3=Andrey|last4=Nettersheim|first4=Benjamin J.|last5=Hallmann|first5=Christian|last6=Brocks|first6=Jochen J.|date=2018-09-21|title=Ancient steroids establish the Ediacaran fossil Dickinsonia as one of the earliest animals|journal=Science|language=en|volume=361|issue=6408|pages=1246–1249|doi=10.1126/science.aat7228|issn=0036-8075|pmid=30237355|bibcode=2018Sci...361.1246B|doi-access=free|hdl=1885/230014|hdl-access=free}} Other researchers have suggested that the elusive trace fossil Paleodictyon and its relatives may represent a fossil xenophyophore{{Cite journal|last=Swinbanks|first=D. D.|s2cid=28690086|date=1982-10-01|title=Piaeodicton: The Traces of Infaunal Xenophyophores?|url=https://www.science.org/doi/10.1126/science.218.4567.47|journal=Science|language=en|volume=218|issue=4567|pages=47–49|doi=10.1126/science.218.4567.47|issn=0036-8075|pmid=17776707|bibcode=1982Sci...218...47S|url-access=subscription}} and noted the similarity of the extant xenophyophore Occultammina to the fossil;{{Cite journal|last=Levin|first=Lisa A.|date=1994|title=Paleoecology and Ecology of Xenophyophores|journal=PALAIOS|volume=9|issue=1|pages=32–41|doi=10.2307/3515076|jstor=3515076|bibcode=1994Palai...9...32L|issn=0883-1351}} 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.{{Cite journal|last1=Rona|first1=Peter A.|last2=Seilacher|first2=Adolf|last3=de Vargas|first3=Colomban|last4=Gooday|first4=Andrew J.|last5=Bernhard|first5=Joan M.|last6=Bowser|first6=Sam|last7=Vetriani|first7=Costantino|last8=Wirsen|first8=Carl O.|last9=Mullineaux|first9=Lauren|last10=Sherrell|first10=Robert|last11=Frederick Grassle|first11=J.|date=2009-09-01|title=Paleodictyon nodosum: A living fossil on the deep-sea floor|url=http://www.sciencedirect.com/science/article/pii/S0967064509001799|journal=Deep Sea Research Part II: Topical Studies in Oceanography|series=Marine Benthic Ecology and Biodiversity: A Compilation of Recent Advances in Honor of J. Frederick Grassle|language=en|volume=56|issue=19|pages=1700–1712|doi=10.1016/j.dsr2.2009.05.015|bibcode=2009DSRII..56.1700R|issn=0967-0645|url-access=subscription}} 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.{{Cite journal|last1=Gooday|first1=Andrew J|last2=Holzmann|first2=Maria|last3=Caulle|first3=Clémence|last4=Goineau|first4=Aurélie|last5=Kamenskaya|first5=Olga|last6=Weber|first6=Alexandra A. -T.|last7=Pawlowski|first7=Jan|date=2017-03-01|title=Giant protists (xenophyophores, Foraminifera) are exceptionally diverse in parts of the abyssal eastern Pacific licensed for polymetallic nodule exploration|journal=Biological Conservation|language=en|volume=207|pages=106–116|doi=10.1016/j.biocon.2017.01.006|issn=0006-3207|doi-access=free}}

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.{{Cite journal|last1=McIlroy|first1=Duncan|last2=Green|first2=O. R.|last3=Brasier|first3=M. D.|date=2001|title=Palaeobiology and evolution of the earliest agglutinated Foraminifera: Platysolenites, Spirosolenites and related forms|journal=Lethaia|language=en|volume=34|issue=1|pages=13–29|doi=10.1080/002411601300068170|issn=1502-3931}}{{Cite journal|last1=Kontorovich|first1=A. E.|last2=Varlamov|first2=A. I.|last3=Grazhdankin|first3=D. V.|last4=Karlova|first4=G. A.|last5=Klets|first5=A. G.|last6=Kontorovich|first6=V. A.|last7=Saraev|first7=S. V.|last8=Terleev|first8=A. A.|last9=Belyaev|first9=S. Yu.|last10=Varaksina|first10=I. V.|last11=Efimov|first11=A. S.|date=2008-12-01|title=A section of Vendian in the east of West Siberian Plate (based on data from the Borehole Vostok 3)|url=http://www.sciencedirect.com/science/article/pii/S106879710800206X|journal=Russian Geology and Geophysics|language=en|volume=49|issue=12|pages=932–939|doi=10.1016/j.rgg.2008.06.012|bibcode=2008RuGG...49..932K|issn=1068-7971|url-access=subscription}}

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.{{Cite journal|last1=Scott|first1=David B.|last2=Medioli|first2=Franco|last3=Braund|first3=Regan|date=2003-06-01|title=Foraminifera from the Cambrian of Nova Scotia: The oldest multichambered foraminifera|url=https://pubs.geoscienceworld.org/micropal/article-abstract/49/2/109/125201/Foraminifera-from-the-Cambrian-of-Nova-Scotia-The|journal=Micropaleontology|language=en|volume=49|issue=2|pages=109–126|doi=10.2113/49.2.109|issn=1937-2795|url-access=subscription}}{{Cite journal|last1=Pawlowski|first1=Jan|last2=Holzmann|first2=Maria|last3=Tyszka|first3=Jarosław|date=2013-04-01|title=New supraordinal classification of Foraminifera: Molecules meet morphology|url=http://www.sciencedirect.com/science/article/pii/S0377839813000327|journal=Marine Micropaleontology|language=en|volume=100|pages=1–10|doi=10.1016/j.marmicro.2013.04.002|bibcode=2013MarMP.100....1P|issn=0377-8398|url-access=subscription}} 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.{{Cite journal|last1=Tappan|first1=Helen|last2=Loeblich|first2=Alfred R.|date=1988|title=Foraminiferal Evolution, Diversification, and Extinction|journal=Journal of Paleontology|volume=62|issue=5|pages=695–714|jstor=1305391|issn=0022-3360}}

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 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.{{Citation|last1=Saraswati|first1=Pratul Kumar|title=Calcareous-Walled Microfossils|date=2016|work=Micropaleontology: Principles and Applications|pages=81–119|editor-last=Saraswati|editor-first=Pratul Kumar|publisher=Springer International Publishing|language=en|doi=10.1007/978-3-319-14574-7_6|isbn=978-3-319-14574-7|last2=Srinivasan|first2=M. S.|editor2-last=Srinivasan|editor2-first=M.S.}}{{Cite web|title=Fusulinids {{!}} GeoKansas|url=http://geokansas.ku.edu/fusulinids|website=geokansas.ku.edu|access-date=2020-05-16}}

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 Cretaceous.

The earliest Involutinid fossils appear during the Permian; the lineage diversified throughout the Mesozoic of Eurasia before apparently vanishing from the fossil record following the Cenomanian-Turonian Ocean Anoxic Event. The extant group planispirillinidae has been referred to the involutinida, but this remains the subject of debate.{{Cite web|title=PBDB Navigator|url=https://paleobiodb.org/navigator/#/b191337c|last=Czaplewski|first=John J.|website=paleobiodb.org|access-date=2020-05-16}}

The Robertinida first appear in the fossil record during the Anisian epoch of the Triassic. The group remained at low diversity throughout its fossil history; all living representatives belong to the Robertinidae, which first appeared during the Paleocene.

The first definite Rotaliid fossils do not appear in the fossil record until the Pliensbachian epoch of the Jurassic, following the Triassic-Jurassic event.{{Cite journal|last=Gräfe|first=K.U.|s2cid=55664447|date=2005|title=Benthic foraminifers and palaeoenvironment in the Lower and Middle Jurassic of the Western Basque-Cantabrian Basin (Northern Spain)|journal=Journal of Iberian Geology|volume=31|issue=2|pages=217–233}} Diversity of the group remained low until the aftermath of the Cenomanian-Turonian event, after which the group saw a rapid diversification. Of this group, the planktonic Globigerinina—the first known group of planktonic forams—first appears in the aftermath of the Toarcian Turnover; the group saw heavy losses during both the K-Pg extinction and the Eocene-Oligocene extinction, but remains extant and diverse to this day. An additional evolution of planktonic lifestyle occurred in the Miocene or Pliocene, when the rotaliid Neogallitellia independently evolved a planktonic lifestyle.{{Cite journal|last1 =Ujiié|first1 =Yurika|last2=Kimoto|first2 =Katsunori|last3 =Pawlowski|first3 =Jan|date =December 2008|title =Molecular evidence for an independent origin of modern triserial planktonic foraminifera from benthic ancestors|journal=Marine Micropaleontology|language=en|volume=69|issue=3–4|pages=334–340|doi=10.1016/j.marmicro.2008.09.003|bibcode =2008MarMP..69..334U}}{{Cite journal|last =Özdikmen|first =Hüseyin|date =June 2009|title =Substitute names for some unicellular animal taxa (Protozoa|url =https://www.munisentzool.org/yayin/vol4/issue2/MEZVol4No2.pdf|journal=Munis Entomology & Zoology|volume=4|issue=1|pages=233–256}}

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| image1 = Micro-CT model of radiolarian, Triplococcus acanthicus.png

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| caption1 = {{center|X-ray microtomography of Triplococcus acanthicus}} This is a microfossil from the Middle Ordovician with four nested spheres. The innermost sphere is highlighted red. Each segment is shown at the same scale.{{cite journal|last1=Kachovich|first1=S.|last2=Sheng|first2=J.|last3=Aitchison|first3=J.C.|year=2019|title=Adding a new dimension to investigations of early radiolarian evolution|journal=Scientific Reports|volume=9|issue=1|pages=1–10|doi=10.1038/s41598-019-42771-0|pmid=31015493 |pmc=6478871|bibcode=2019NatSR...9.6450K }}. 50px Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].

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The earliest known radiolaria date to the very start of the Cambrian period,{{cite journal |last1=Chang |first1=Shan |last2=Feng |first2=Qinglai |last3=Zhang |first3=Lei |title=New Siliceous Microfossils from the Terreneuvian Yanjiahe Formation, South China: The Possible Earliest Radiolarian Fossil Record |journal=Journal of Earth Science |date=14 August 2018 |volume=29 |issue=4 |pages=912–919 |doi=10.1007/s12583-017-0960-0|s2cid=134890245 }}{{cite journal |last1=Zhang |first1=Ke |last2=Feng |first2=Qing-Lai |title=Early Cambrian radiolarians and sponge spicules from the Niujiaohe Formation in South China |journal=Palaeoworld |date=September 2019 |volume=28 |issue=3 |pages=234–242 |doi=10.1016/j.palwor.2019.04.001|s2cid=146452469 }}{{cite journal |last1=Maletz |first1=Jörg |title=The identification of putative Lower Cambrian Radiolaria |journal=Revue de Micropaléontologie |date=June 2017 |volume=60 |issue=2 |pages=233–240 |doi=10.1016/j.revmic.2017.04.001|bibcode=2017RvMic..60..233M }} appearing in the same beds as the first small shelly fauna—they may even be terminal Precambrian in age. They have significant differences from later radiolaria, with a different silica lattice structure and few, if any, spikes on the test.{{the Rise and Fall of the Ediacaran Biota |author=A. Braun |author2=J. Chen |author3=D. Waloszek |author4=A. Maas |chapter=First Early Cambrian Radiolaria |pages=143–149 |doi=10.1144/SP286.10}} Ninety percent of radiolarian species are extinct. The skeletons, or tests, of ancient radiolarians are used in geological dating, including for oil exploration and determination of ancient climates.{{cite journal|last1=Zuckerman|first1=L.D.|last2=Fellers|first2=T.J.|last3=Alvarado|first3=O.|last4=Davidson|first4=M.W.|url=http://micro.magnet.fsu.edu/micro/gallery/radiolarians/radiolarians.html|title=Radiolarians|journal=Molecular Expressions|publisher=Florida State University|date=4 February 2004}}

Some common radiolarian fossils include Actinomma, Heliosphaera and Hexadoridium.{{citation needed|date=July 2023}}

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File:Evolutionary history of coccolithophores.jpg Material was copied from this source, which is available under a [https://creativecommons.org/licenses/by/4.0/ Creative Commons Attribution 4.0 International License].}} (A) Coccolithophore species richness over time
(B) The fossil record of major coccolithophore biomineralization innovations and morphogroups]]

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• Coccolithophores: The diagram on the right shows —>

(A) coccolithophore species richness over time combining heterococcoliths and nannoliths.{{cite book|author=Bown P. R., Lees J. A. and Young J. R.|year=2004|chapter=Calcareous nannoplankton evolution and diversity through time|title=Coccolithophores: From Molecular Processes to Global Impacts|editor1=H. Thierstein|editor2=J. R. Young|publisher=Springer|pages=481–508}} Q, Quaternary; N, Neogene; Pal, Paleogene; E/O, Eocene/Oligocene glacial onset event; PETM, Paleocene/Eocene thermal maximum warming event; K/Pg, Cretaceous/Paleogene; OAE, oceanic anoxic event; T-OAE, Toarcian oceanic anoxic event; T/J, Triassic/Jurassic; P/T, Permian/Triassic; mass ext., mass extinction.

(B) the fossil record of major coccolithophore biomineralization innovations and morphogroups, including the first appearances of muroliths (simple coccoliths with narrow, wall-like rims), placoliths (coccoliths with broad shields that interlock to form strong coccospheres), holococcoliths (coccoliths formed from microcrystals in the haploid life cycle phase), Braarudosphaera (pentagonal, laminated nannoliths forming dodecahedral coccospheres); Calciosolenia (distinct, rhombic murolith coccoliths), Coccolithus (long-ranging and abundant Cenozoic genus), Isochrysidales (dominant order that includes Emiliania, Gephyrocapsa, and Reticulofenestra). Significant mass extinctions and paleoceanographic/paleoclimatic events are marked as horizontal lines.

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(in part)

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Because many of these organisms had a silica capsule, they have a relatively complete fossil record, allowing modern biologists to confirm that they are, in fact, not derived from cyanobacteria, but rather an ancestor that did not possess the capability to photosynthesize. Many of the chrysophyta precursor fossils entirely lacked any type of photosynthesis-capable pigment. Most biologists believe that the chrysophytes obtained their ability to photosynthesize from an endosymbiotic relationship with fucoxanthin-containing cyanobacteria.

The ancestral green alga was a unicellular flagellate.

• Marine sediment
• Microfossils
• Protist shells
• List of prehistoric foraminifera genera

{{Notelist|1}}

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Category:Evolution

Category:Protists

Category:Micropaleontology