Editing Microfossil (section)

==Organic-walled==

===Palynomorphs===
{{further|Palynomorphs|Kerogen}}

===Pollen grain===
[[File:Trilete spores.png|thumb|upright=1.3| {{center|[[Late Silurian]] [[sporangium]] bearing [[trilete spore]]s provide the earliest evidence of life on land.<ref name=Gray1985>{{cite journal| author = Gray, J.| date = 1985| title = The Microfossil Record of Early Land Plants: Advances in Understanding of Early Terrestrialization, 1970&ndash;1984| journal = [[Philosophical Transactions of the Royal Society B]] | volume = 309| issue = 1138| pages = 167–195| doi  = 10.1098/rstb.1985.0077| last2 = Chaloner| first2 = W. G.| last3  = Westoll| first3 = T. S.| jstor=2396358| bibcode=1985RSPTB.309..167G| doi-access = free}}</ref><br /><small>Green: spore tetrad. Blue: spore with Y-shaped trilete mark.<br />Spores are about 30&ndash;35&nbsp;μm across</small>}}]]
{{see also|Pollen zone}}

[[Pollen]] has an outer sheath, called a  [[sporopollenin]], which affords it some resistance to the rigours of the fossilisation process that destroy weaker objects. It is produced in huge quantities. There is an extensive fossil record of pollen grains, often disassociated from their parent plant. The discipline of [[palynology]] is devoted to the study of pollen, which can be used both for biostratigraphy and to gain information about the abundance and variety of plants alive — which can itself yield important information about paleoclimates. Also, pollen analysis has been widely used for reconstructing past changes in vegetation and their associated drivers.<ref>{{cite journal |last=Franco-Gaviria |first=Felipe |display-authors=etal |title=The human impact imprint on modern pollen spectra of the Mayan lands |year=2018 |journal=[[Boletín de la Sociedad Geológica Mexicana]] |volume=70 |issue=1 |pages=61–78 |doi=10.18268/BSGM2018v70n1a4 |url=http://boletinsgm.igeolcu.unam.mx/bsgm/vols/epoca04/7001/%284%29Franco.pdf|doi-access=free }}</ref>
Pollen is first found in the [[fossil]] record in the late [[Devonian]] period,<ref name="palynology">{{Cite book| last = Traverse | first = Alfred | chapter = Devonian Palynology | pages=199–227 | title = Paleopalynology | volume = 28 |series = Topics in Geobiology, 28 | year =2007 | publisher = Springer | location = Dordrecht | isbn = 978-1-4020-6684-9 | doi = 10.1007/978-1-4020-5610-9_8 }}</ref><ref>{{cite journal |last1=Wang |first1=De-Ming |last2=Meng |first2=Mei-Cen |last3=Guo |first3=Yun |title=Pollen Organ Telangiopsis sp. of Late Devonian Seed Plant and Associated Vegetative Frond |year=2016 |journal=PLOS ONE |volume=11 |issue=1 |pages=e0147984 |doi=10.1371/journal.pone.0147984 |pmid=26808271 |pmc=4725745 |bibcode=2016PLoSO..1147984W |doi-access=free }}</ref> but at that time it is indistinguishable from spores.<ref name="palynology"/> It increases in abundance until the present day.

===Plant spores===
{{see also|Cryptospore}}

A [[spore]] is a unit of [[sexual reproduction|sexual]] or [[asexual reproduction]] that may be adapted for [[biological dispersal|dispersal]] and for survival, often for extended periods of time, in unfavourable conditions. Spores form part of the [[Biological life cycle|life cycles]] of many [[plant]]s, [[algae]], [[fungus|fungi]] and [[protozoa]].<ref>{{Cite web |url=http://tolweb.org/tree/home.pages/searchresults.html?cx=009557456284541951685%3A50nf_5tpvuq&cof=FORID%3A9&ie=UTF-8&q=spore&sa=Search |title=Tree of Life Web Project |access-date=5 February 2018 |archive-url=https://web.archive.org/web/20180205184645/http://tolweb.org/tree/home.pages/searchresults.html?cx=009557456284541951685%3A50nf_5tpvuq&cof=FORID%3A9&ie=UTF-8&q=spore&sa=Search |archive-date=5 February 2018 |url-status=live }}</ref> [[Bacterial spore]]s are not part of a sexual cycle but are resistant structures used for survival under unfavourable conditions.

===Fungal spores===

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===Chitinozoa===
[[File:Whole_chitinozoan_cropped.jpg|thumb| A [[Late Silurian]] chitinozoan from the [[Burgsvik beds]] showing its flask shape]]

[[Chitinozoa]] are a [[taxon]] of [[laboratory flask|flask]]-shaped, [[organic matter|organic]] walled [[marine biology|marine]] microfossils produced by an as-yet-unknown organism.<ref name=Mullins>{{cite journal| doi=10.1111/1475-4983.00131| title=A chitinozoan morphological lineage and its importance in Lower Silurian stratigraphy| author= Gary Lee Mullins| year=2000| journal=Palaeontology| volume=43| pages=359–373| issue=2| bibcode=2000Palgy..43..359M| doi-access=free}}</ref>

Common from the [[Ordovician]] to [[Devonian]] periods (i.e. the mid-Paleozoic), the millimetre-scale organisms are abundant in almost all types of [[marine sediment]] across the globe.<ref name=Jansonius1978>{{cite book | author = Jansonius, J. |author2=Jenkins, W.A.M.| year = 1978 | chapter = Chitinozoa | isbn = 0-444-00267-7 | title = Introduction to marine micropaleontology. | publisher = Elsevier, New York | pages = 341–357}}</ref> This wide distribution, and their rapid pace of evolution, makes them valuable [[biostratigraphic]] markers.

Their bizarre form has made [[scientific classification|classification]] and ecological reconstruction difficult.  Since their discovery in 1931, suggestions of [[protist]], [[plant]], and [[fungus|fungal]] affinities have all been entertained.  The organisms have been better understood as improvements in microscopy facilitated the study of their fine structure, and it has been suggested that they represent either the [[egg (biology)|eggs]] or juvenile stage of a marine animal.<ref name=Gabbott1998>{{cite journal | author = Gabbott, S.E. |author2=Aldridge, R.J. |author3=Theron, J.N. | year = 1998 | title = Chitinozoan chains and cocoons from the Upper Ordovician Soom Shale lagerstatte, South Africa; implications for affinity | journal = Journal of the Geological Society | volume = 155 | issue = 3 | pages = 447–452 | doi = 10.1144/gsjgs.155.3.0447| bibcode = 1998JGSoc.155..447G|s2cid=129236534 }}</ref> However, recent research has suggested that they represent the [[Test (biology)|test]] of a group of protists with uncertain affinities.<ref name=Liang2020>{{Cite journal|last1=Liang|first1=Yan|last2=Hints|first2=Olle|last3=Tang|first3=Peng|last4=Cai|first4=Chenyang|last5=Goldman|first5=Daniel|last6=Nõlvak|first6=Jaak|last7=Tihelka|first7=Erik|last8=Pang|first8=Ke|last9=Bernardo|first9=Joseph|last10=Wang|first10=Wenhui|date=2020-12-01|title=Fossilized reproductive modes reveal a protistan affinity of Chitinozoa|journal=Geology|language=en|volume=48|issue=12|pages=1200–1204|doi=10.1130/G47865.1|bibcode=2020Geo....48.1200L|issn=0091-7613|doi-access=free}}</ref>

The ecology of chitinozoa is also open to speculation; some may have floated in the water column, where others may have attached themselves to other organisms.  Most species were particular about their living conditions, and tend to be most common in specific paleoenvironments. Their abundance also varied with the seasons.

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===Acritarchs===
[[File:Acritarch from the Weng'an biota.jpg|thumb| {{center|Acritarch from the Weng'an biota<br />c. 570–609 [[MYA (unit)|mya]] {{hsp}}<ref>{{cite journal |doi = 10.1144/jgs2016-142|title = The Weng'an Biota (Doushantuo Formation): An Ediacaran window on soft-bodied and multicellular microorganisms|year = 2017|last1 = Cunningham|first1 = John A.|last2 = Vargas|first2 = Kelly|last3 = Yin|first3 = Zongjun|last4 = Bengtson|first4 = Stefan|last5 = Donoghue|first5 = Philip C. J.|journal = Journal of the Geological Society|volume = 174|issue = 5|pages = 793–802|bibcode = 2017JGSoc.174..793C|doi-access = free|hdl = 1983/d874148a-f20e-498a-97d2-379b3feaa18a|hdl-access = free}}</ref>
}}]]

[[Acritarch]]s, Greek for ''confused origins'',<ref>definition of [http://dictionary.reference.com/browse/acritarch acritarch] at [[dictionary.com]]</ref> are organic-walled microfossils, known from about {{Ma|2000}} to the present. Acritarchs are not a specific biological taxon, but rather a group with uncertain or unknown affinities.<ref name=Evitt1963>{{cite journal |doi = 10.1073/pnas.49.3.298|title = A Discussion and Proposals Concerning Fossil Dinoflagellates, Hystrichospheres, and Acritarchs, Ii|year = 1963|last1 = Evitt|first1 = W. R.|journal = Proceedings of the National Academy of Sciences|volume = 49|issue = 3|pages = 298–302|pmid = 16591055|pmc = 299818|bibcode = 1963PNAS...49..298E|doi-access = free}}</ref><ref>{{cite journal |doi = 10.1111/j.1469-185X.1993.tb01241.x|title = Acritarchsa Review|year = 1993|last1 = Martin|first1 = Francine|journal = Biological Reviews|volume = 68|issue = 4|pages = 475–537|s2cid = 221527533}}</ref><ref>{{cite journal |doi = 10.1016/0034-6667(94)00148-D|title = Review of biological affinities of Paleozoic acid-resistant, organic-walled eukaryotic algal microfossils (Including "acritarchs")|year = 1995|last1 = Colbath|first1 = G.Kent|last2 = Grenfell|first2 = Hugh R.|journal = Review of Palaeobotany and Palynology|volume = 86|issue = 3–4|pages = 287–314| bibcode=1995RPaPa..86..287C }}</ref> Most commonly they are composed of thermally altered acid insoluble carbon compounds ([[kerogen]]). While the [[biological classification|classification]] of acritarchs into [[form taxon|form genera]] is entirely artificial, it is not without merit, as the form taxa show traits similar to those of genuine [[taxon|taxa]] — for example the '[[Cambrian explosion|explosion]]' in the [[Cambrian]] and the [[mass extinction]] at the [[Permian-Triassic extinction event|end]] of the [[Permian]].

Acritarch diversity reflects major ecological events such as the appearance of predation and the [[Cambrian explosion]]. Precambrian marine diversity was dominated by acritarchs. They underwent a boom around {{Ma|1000}}, increasing in abundance, diversity, size, complexity of shape, and especially size and number of spines. Their increasingly spiny forms in the last 1 billion years may indicate an increased need for defence against predation.<ref>{{Cite book| author=Bengtson, S. | year=2002 | contribution=Origins and early evolution of predation | title=The fossil record of predation. The Paleontological Society Papers 8 | editor=Kowalewski, M. |editor2=Kelley, P.H. | pages=289–317 | publisher=The Paleontological Society | url=http://www.nrm.se/download/18.4e32c81078a8d9249800021552/Bengtson2002predation.pdf | format = Free full text| access-date=2007-12-01}}</ref>

Acritarchs may include the remains of a wide range of quite different kinds of organisms—ranging from the egg cases of small [[metazoan]]s to resting cysts of many kinds of [[chlorophyta]] (green algae). It is likely that most acritarch species from the [[Paleozoic]] represent various stages of the life cycle of algae that were ancestral to the [[dinoflagellates]].<ref>{{Cite journal |last1=Colbath|first1= G.Kent|last2=Grenfell|first2= Hugh R.|date= 1995|title= Review of biological affinities of Paleozoic acid-resistant, organic-walled eukaryotic algal microfossils (including "acritarchs")|journal =Review of Palaeobotany and Palynology|volume =86|issue =3–4|pages =287–314|doi=10.1016/0034-6667(94)00148-d|bibcode= 1995RPaPa..86..287C|issn =0034-6667}}</ref> The nature of the organisms associated with older acritarchs is generally not well understood, though many are probably related to unicellular marine [[alga]]e. In theory, when the biological source (taxon) of an acritarch does become known, that particular microfossil is removed from the acritarchs and classified with its proper group.

Acritarchs were most likely [[eukaryote]]s. While archaea, bacteria and cyanobacteria ([[prokaryotes]]) usually produce simple fossils of a very small size, eukaryotic unicellular fossils are usually larger and more complex, with external morphological projections and ornamentation such as spines and hairs that only eukaryotes can produce; as most acritarchs have external projections (e.g., hair, spines, thick cell membranes, etc.), they are predominantly eukaryotes, although simple eukaryote acritarchs also exist.<ref>{{Cite journal| doi = 10.1038/463885a| pmid = 20164911| year = 2010| last1 = Buick | first1 = R. .| title = Early life: Ancient acritarchs| volume = 463| issue = 7283| pages = 885–886| journal = Nature |bibcode = 2010Natur.463..885B | doi-access = free}}</ref>

Acritarchs are found in sedimentary rocks from the present back into the [[Archean]].<ref>{{cite journal | title=MONTENARI, M. & LEPPIG, U. (2003): The Acritarcha: their classification morphology, ultrastructure and palaeoecological/palaeogeographical distribution. | journal=Paläontologische Zeitschrift | year=2003 | volume=77 | pages=173–194 | doi=10.1007/bf03004567| s2cid=127238427 }}</ref> They are typically isolated from siliciclastic sedimentary rocks using [[hydrofluoric acid]] but are occasionally extracted from carbonate-rich rocks. They are excellent candidates for index fossils used for dating rock formations in the [[Palaeozoic|Paleozoic]] Era and when other fossils are not available. Because most acritarchs are thought to be marine (pre-Triassic), they are also useful for palaeoenvironmental interpretation. The Archean and earliest [[Proterozoic]] microfossils termed "acritarchs" may actually be prokaryotes. The earliest eukaryotic acritarchs known (as of 2020) are from between 1950 and 2150 million years ago.<ref>{{cite journal |last1=Yin |first1=Leiming |title=Microfossils from the Paleoproterozoic Hutuo Group, Shanxi, North China: Early evidence for eukaryotic metabolism |journal=Precambrian Research |volume=342 |pages=105650 |date=Feb 2020 |doi=10.1016/j.precamres.2020.105650|bibcode=2020PreR..342j5650Y |doi-access=free }}</ref>

Recent application of [[atomic force microscopy]], [[confocal microscopy]], [[Raman spectroscopy]], and other analytic techniques to the study of the ultrastructure, life history, and systematic affinities of mineralized, but originally organic-walled microfossils,<ref>{{cite journal |doi = 10.1073/pnas.142310299|title = Atomic force microscopy of Precambrian microscopic fossils|year = 2002|last1 = Kempe|first1 = A.|last2 = Schopf|first2 = J. W.|last3 = Altermann|first3 = W.|last4 = Kudryavtsev|first4 = A. B.|last5 = Heckl|first5 = W. M.|journal = Proceedings of the National Academy of Sciences|volume = 99|issue = 14|pages = 9117–9120|pmid = 12089337|pmc = 123103|bibcode = 2002PNAS...99.9117K|doi-access = free}}</ref><ref>{{cite journal |doi = 10.1016/j.precamres.2005.07.002|title = Focussed ion beam preparation and in situ nanoscopic study of Precambrian acritarchs|year = 2005|last1 = Kempe|first1 = A.|last2 = Wirth|first2 = R.|last3 = Altermann|first3 = W.|last4 = Stark|first4 = R.|last5 = Schopf|first5 = J.|last6 = Heckl|first6 = W.|journal = Precambrian Research|volume = 140|issue = 1–2|pages = 36–54|bibcode = 2005PreR..140...36K}}</ref><ref>{{cite journal |doi = 10.1016/j.precamres.2005.05.006|title = Combined micro-Fourier transform infrared (FTIR) spectroscopy and micro-Raman spectroscopy of Proterozoic acritarchs: A new approach to Palaeobiology|year = 2005|last1 = Marshall|first1 = C.|last2 = Javaux|first2 = E.|last3 = Knoll|first3 = A.|last4 = Walter|first4 = M.|journal = Precambrian Research|volume = 138|issue = 3–4|pages = 208–224|bibcode = 2005PreR..138..208M}}</ref><ref>{{cite journal |doi = 10.4202/app.2008.0060|title = Spore-Like Bodies in Some Early Paleozoic Acritarchs: Clues to Chlorococcalean Affinities|year = 2009|last1 = Kaźmierczak|first1 = Józef|last2 = Kremer|first2 = Barbara|journal = Acta Palaeontologica Polonica|volume = 54|issue = 3|pages = 541–551|doi-access = free}}</ref><ref>{{cite journal |doi = 10.1666/09-134.1|title = Confocal laser scanning microscopy and Raman imagery of the late Neoproterozoic Chichkan microbiota of South Kazakhstan|year = 2010|last1 = Schopf|first1 = J. William|last2 = Kudryavtsev|first2 = Anatoliy B.|last3 = Sergeev|first3 = Vladimir N.|journal = Journal of Paleontology|volume = 84|issue = 3|pages = 402–416| bibcode=2010JPal...84..402S |s2cid = 130041483}}</ref> have shown some acritarchs are fossilized [[microalgae]]. In the end, it may well be, as Moczydłowska et al. suggested in 2011, that many acritarchs will, in fact, turn out to be algae.<ref>{{cite journal |doi = 10.1111/j.1475-4983.2011.01054.x|title = Proterozoic phytoplankton and timing of Chlorophyte algae origins|year = 2011|last1 = Moczydłowska|first1 = Małgorzata|last2 = Landing|first2 = ED|last3 = Zang|first3 = Wenlong|last4 = Palacios|first4 = Teodoro|journal = Palaeontology|volume = 54|issue = 4|pages = 721–733| bibcode=2011Palgy..54..721M |doi-access = free}}</ref><ref name=Chamberlain2016>{{cite journal |doi = 10.3390/geosciences6040057|title = A Mineralized Alga and Acritarch Dominated Microbiota from the Tully Formation (Givetian) of Pennsylvania, USA|year = 2016|last1 = Chamberlain|first1 = John|last2 = Chamberlain|first2 = Rebecca|last3 = Brown|first3 = James|journal = Geosciences|volume = 6|issue = 4|page = 57|bibcode = 2016Geosc...6...57C|doi-access = free}} [[File:CC-BY icon.svg|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].</ref>

[[File:Microfossil Morphologies-1.png|thumb|upright=1.3|Three main types of [[Archean]] cell morphologies]]

===Archean cells===
{{see also|Archean life in the Barberton Greenstone Belt}}

Cells can be preserved in the [[rock record]] because their cell walls are made of proteins which convert to the organic material [[kerogen]] as the cell breaks down after death. Kerogen is [[insoluble]] in mineral [[acids]], [[base (chemistry)|base]]s, and [[organic solvents]].<ref>{{cite journal|last=Philp|first=R.P.|author2=Calvin, M. |title=Possible origin for insoluble organic (kerogen) debris in sediments from insoluble cell-wall materials of algae and bacteria|journal=Nature|year=1976|volume=262|pages=134–136 |doi=10.1038/262134a0|issue=5564|bibcode = 1976Natur.262..134P |s2cid=42212699}}</ref> Over time, it is mineralised into [[graphite]] or graphite-like [[carbon]], or degrades into oil and gas hydrocarbons.<ref>{{cite journal|last=Tegelaar|first=E.W.|author2=deLeeuw, J.W.|author3=Derenne, S.|author4=Largeau, C. |title=A reappraisal of kerogen formation|journal=Geochimica et Cosmochimica Acta|year=1989|volume=53|issue=11|pages=3103–3106 |doi=10.1016/0016-7037(89)90191-9|bibcode=1989GeCoA..53.3103T}}</ref> There are three main types of cell morphologies. Though there is no established range of sizes for each type, spheroid microfossils can be as small as about 8&nbsp;[[micrometre]]s, filamentous microfossils have diameters typically less than 5&nbsp;micrometres and have a length that can range from tens of micrometres to 100&nbsp;micrometres, and spindle-like microfossils can be as long as 50&nbsp;micrometres.<ref name=Walsh>{{cite journal|last=Walsh|first=M.|title=Microfossils and possible microfossils from the early Archean Onverwacht Group, Barberton mountain land, South Africa |journal=[[Precambrian Research]]|year=1991|volume=54|issue=2–4|pages=271–293 |pmid=11540926 |doi=10.1016/0301-9268(92)90074-X}}</ref><ref>{{cite journal|author=Oehler, D.Z. |author2=Robert, F. |author3=Mostefaoui, S. |author4=Meibom, A. |author5=Selo, M. |author6=McKay, D.S.|title=Chemical Mapping of Proterozoic Organic Matter at Submicron Spatial Resolution|journal=Astrobiology|year=2006|volume=6|issue=6|pages=838–850 |pmid=17155884 |doi=10.1089/ast.2006.6.838|bibcode = 2006AsBio...6..838O |hdl=2060/20060028086 |hdl-access=free }}</ref>

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