View source for Ediacaran biota

{{Short description|Life of the Ediacaran period}}
{{Other uses|Ediacara (disambiguation){{!}}Ediacara}}
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{{use dmy dates|date=December 2022}}
{{Featured article}}
[[File:Ediacaran sea.png|thumb|upright=1.25|Life in the Ediacaran Period as imagined by researchers in 1980.]]
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The '''Ediacaran''' ({{IPAc-en|ˌ|iː|d|i|ˈ|æ|k|ər|ə|n}}; formerly '''Vendian''') '''biota''' is a [[Taxonomy (biology)|taxonomic]] period classification that consists of all life forms that were present on Earth during the [[Ediacaran]] Period ({{circa| 635–538.8 [[myr|Mya]]}}). These were enigmatic tubular and frond-shaped, mostly [[sessility (zoology)|sessile]], organisms.<ref name=NAT-20201028>{{cite journal |last=Watson |first=Traci |date=28 October 2020 |title=These bizarre ancient species are rewriting animal evolution |type=news |journal=[[Nature (journal)|Nature]] |volume=586 |issue=7831 |pages=662–665 |doi=10.1038/d41586-020-02985-z |doi-access=free |pmid=33116283 |bibcode=2020Natur.586..662W}}</ref><ref name="StratChart 2022">{{cite report |title=Stratigraphic chart 2022 |date=February 2022 |publisher=[[International Stratigraphic Commission]] |url=https://stratigraphy.org/ICSchart/ChronostratChart2022-02.pdf |access-date=22 April 2022 |archive-date=2 April 2022 |archive-url=https://web.archive.org/web/20220402100018/https://stratigraphy.org/ICSchart/ChronostratChart2022-02.pdf |url-status=live }}</ref> [[Trace fossil]]s of these organisms have been found worldwide, and represent the earliest known complex [[multicellular organism]]s. The term "Ediacara biota" has received criticism from some scientists due to its alleged inconsistency, arbitrary exclusion of certain fossils, and inability to be precisely defined.<ref>{{cite journal |last1=MacGabhann |first1=Breandán Anraoi |date=January 2014 |title=There is no such thing as the 'Ediacara Biota' |url=https://www.sciencedirect.com/science/article/pii/S1674987113001096 |journal=Geoscience Frontiers |volume=5 |issue=1 |pages=53–62 |doi=10.1016/j.gsf.2013.08.001 |bibcode=2014GeoFr...5...53M |access-date=12 March 2023 |hdl=20.500.11820/23ba9403-9b3f-484e-8a0f-21587c6baf67 |s2cid=56111824 |hdl-access=free |archive-date=13 March 2023 |archive-url=https://web.archive.org/web/20230313054311/https://www.sciencedirect.com/science/article/pii/S1674987113001096 |url-status=live }}</ref>

The Ediacaran biota may have undergone [[evolutionary radiation]] in a proposed event called the [[Avalon explosion]], {{Ma|575}}.<ref>{{cite press release |title=Two explosive evolutionary events shaped early history Of multicellular life |date=January 2008 |website=[[Science Daily]] |url=https://www.sciencedaily.com/releases/2008/01/080103144451.htm |access-date=28 February 2018 |archive-date=7 July 2017 |archive-url=https://web.archive.org/web/20170707000732/https://www.sciencedaily.com/releases/2008/01/080103144451.htm |url-status=live }}</ref><ref>{{cite journal | last1=Shen | first1=Bing | last2=Dong | first2=Lin | last3=Xiao | first3=Shuhai | last4=Kowalewski | first4=Michał | year=2008 | title=The Avalon explosion: Evolution of Ediacara morphospace | journal=[[Science (journal)|Science]] | volume=319 | issue=5859 | pages=81–84 | doi=10.1126/science.1150279 | pmid=18174439 | bibcode=2008Sci...319...81S | s2cid=206509488 }}</ref> This was after the Earth had thawed from the [[Cryogenian]] period's [[Snowball Earth|extensive glaciation]]. This biota largely disappeared with the rapid increase in [[biodiversity]] known as the [[Cambrian explosion]]. Most of the currently existing [[body plan]]s of [[animal]]s first appeared in the [[fossil|fossil record]] of the [[Cambrian]] rather than the Ediacaran. For macroorganisms, the Cambrian biota appears to have almost completely replaced the organisms that dominated the Ediacaran fossil record, although relationships are still a matter of debate.

The organisms of the Ediacaran Period first appeared around {{Ma|600}} and flourished until the cusp of the [[Cambrian]] {{Ma|538.8}}, when the characteristic communities of fossils vanished. A diverse Ediacaran community was discovered in 1995 in [[Sonora]], Mexico, and is approximately 555&nbsp;million years in age, roughly coeval with Ediacaran fossils of the [[Ediacara Hills]] in [[South Australia]] and the [[White Sea]] on the coast of [[Russia]].<ref>{{cite journal | last=McMenamin | first=M.A.S. | author-link= Mark A. S. McMenamin | date=14 May 1996 | title=Ediacaran biota from Sonora, Mexico | pmc=39393 | journal=[[Proceedings of the National Academy of Sciences of the United States of America]] | volume=93 | issue=10 | pages=4990–4993 | pmid=11607679 | doi=10.1073/pnas.93.10.4990 | doi-access=free | bibcode=1996PNAS...93.4990M}}</ref><ref>{{cite book | last=McMenamin | first=M.A.S. | author-link=Mark A. S. McMenamin | year=2018 | title=Deep Time Analysis: A Coherent View of the History of Life | publisher=Springer Geology | isbn = 978-3-319-74255-7 | place = Cham, Switzerland }}</ref><ref>{{cite conference |first=Guy |last=Narbonne |year=2008 |title=The Gaskiers glaciation as a significant divide in Ediacaran history and stratigraphy |series=Abstracts |conference=33rd [[International Geological Congress]] |place=Oslo |url=http://www.cprm.gov.br/33IGC/1342961.html |archive-url=https://web.archive.org/web/20131013121217/http://www.cprm.gov.br/33IGC/1342961.html |archive-date=13 October 2013 }}</ref> While rare fossils that may represent survivors have been found as late as the [[Middle Cambrian]] (510–500&nbsp;Mya), the earlier fossil communities [[End-Ediacaran extinction|disappear from the record at the end of the Ediacaran]] leaving only curious fragments of once-thriving [[ecosystem]]s.<ref name=ConwayMorris1993/> Multiple hypotheses exist to explain the disappearance of this biota, including [[preservation bias]], a changing environment, the advent of [[predation|predators]] and competition from other life-forms. A sampling, reported in 2018, of late Ediacaran strata across the scattered remnants of [[Baltica]] {{nobr|(< 560 Mya)}} suggests the flourishing of the organisms coincided with conditions of low overall productivity with a very high percentage produced by bacteria, which may have led to high concentrations of dissolved organic material in the oceans.<ref>{{Cite journal |last1=Bekker |first1=Andrey |last2=Sokur |first2=Tetyana |last3=Shumlyanskyy |first3=Leonid  |last4=Christopher K. Junium |last5=Podkovyrov |first5=Victor |last6=Kuznetsov |first6=Anton |last7=Love |first7=Gordon D. |last8=Pehr |first8=Kelden |display-authors=6 |date=4 May 2018 |title=Ediacara biota flourished in oligotrophic and bacterially dominated marine environments across Baltica |journal=Nature Communications |lang=en |volume=9 |issue=1 |page=1807 |doi=10.1038/s41467-018-04195-8 |pmid=29728614 |issn=2041-1723 |pmc=5935690 |bibcode=2018NatCo...9.1807P}}</ref>

Determining where Ediacaran organisms fit in the [[tree of life (biology)|tree of life]] has proven challenging; it is not even established that most of them were animals, with suggestions that they were [[lichens]] (fungus-alga symbionts), [[algae]], [[protists]] known as [[foraminifera]], [[fungi]] or [[microbial]] colonies, or hypothetical intermediates between plants and animals.<ref name=Pflug /> The morphology and habit of some taxa (e.g. ''[[Funisia dorothea]]'') suggest relationships to [[Porifera]] or [[Cnidaria]] (e.g. ''[[Auroralumina]]'').<ref>{{cite journal | last1=Droser | first1=M.L. | last2=Gehling | first2=J.G. | date=21 March 2008 | title=Synchronous aggregate growth in an abundant new Ediacaran tubular organism | journal=Science | volume=319 | issue=5870 | pages=1660–1662 | doi=10.1126/science.1152595 | pmid=18356525 | bibcode=2008Sci...319.1660D | s2cid=23002564 }}</ref><ref>{{cite journal |last1=Dunn |first1=F.S. |last2=Kenchington |first2=C.G. |last3=Parry |first3=L.A. |last4=Clark |first4=J.W. |last5=Kendall |first5=R.S. |last6=Wilby |first6=P.R. |date=25 July 2022 |title=A crown-group cnidarian from the Ediacaran of Charnwood Forest, UK |journal=Nature Ecology & Evolution |volume=6 |issue=8 |pages=1095–1104 |doi=10.1038/s41559-022-01807-x |pmid=35879540 |pmc=9349040 |bibcode=2022NatEE...6.1095D }}</ref><ref>{{cite news |last=Amos |first=Jonathan |date=25 July 2022 |title=Ancient fossil is earliest known animal predator |website=bbc.co.uk |publisher=[[BBC News]] |url=https://www.bbc.co.uk/news/science-environment-62291954 |access-date=7 August 2022 |archive-date=14 October 2022 |archive-url=https://web.archive.org/web/20221014194820/https://www.bbc.co.uk/news/science-environment-62291954 |url-status=live }}</ref> ''[[Kimberella]]'' may show a similarity to [[mollusc]]s, and other organisms have been thought to possess [[bilateral symmetry]], although this is controversial. Most [[Macrofossil|macroscopic fossil]]s are [[morphology (biology)|morphologically]] distinct from later life-forms: they resemble discs, tubes, mud-filled bags or quilted mattresses. Due to the difficulty of deducing evolutionary relationships among these organisms, some [[palaeontologist]]s have suggested that these represent completely extinct lineages that do not resemble any living organism. Palaeontologist [[Adolf Seilacher]] proposed a separate subkingdom level category '''Vendozoa''' (now renamed '''[[Vendobionta]]''')<ref name=Seilacher1992/> in the Linnaean hierarchy for the Ediacaran biota. If these enigmatic organisms left no descendants, their strange forms might be seen as <!-- is reference to Guy Narbonne intended? --> a "failed experiment" in multicellular life, with later multicellular life evolving independently from unrelated single-celled organisms.<ref>{{cite book | last=Narbonne | first=Guy |date=June 2006 | title=The Origin and Early Evolution of Animals | department=Department of Geological Sciences and Geological Engineering | publisher=Queen's University | url=http://geol.queensu.ca/people/narbonne/recent_pubs1.html | access-date=2016-09-08 |archive-url=https://web.archive.org/web/20150724081804/http://geol.queensu.ca/people/narbonne/recent_pubs1.html |archive-date=2015-07-24}}</ref> A 2018 study confirmed that one of the period's most-prominent and iconic fossils, ''[[Dickinsonia]]'', included [[cholesterol]],<ref name=Bobrov-Hope-etal-2018>{{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=21 September 2018 |title=Ancient steroids establish the Ediacaran fossil Dickinsonia as one of the earliest animals |journal=[[Science (journal)|Science]] |lang=en |volume=361 |issue=6408 |pages=1246–1249 |doi=10.1126/science.aat7228 |doi-access=free |issn=0036-8075 |pmid=30237355 |bibcode=2018Sci...361.1246B|hdl=1885/230014 |hdl-access=free }}</ref> suggesting affinities to animals, fungi, or red algae.<ref>{{cite journal |last=Gold |first=D.A. |year=2018 |title=The slow rise of complex life as revealed through biomarker genetics |journal=Emerging Topics in Life Sciences |volume=2 |issue=2 |pages=191–199 |doi=10.1042/etls20170150 |pmid=32412622 |s2cid=90887224}}</ref>

{{Graphical timeline
<!-- Change this to help=on if you need instructions on editing this timeline -->
|help=off

|title=The Ediacara biota in context
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|plot-colour=#ffffff

|from=-655
|to=-490
|scale-increment=10
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<!--Eras-->
|legend1=[[Neoproterozoic]]
<br />(last [[Era (geology)|era]] of the [[Precambrian]])
|legend1-colour={{period color|neoproterozoic}}
|bar1-from=-655
|bar1-to=-538.8
|bar1-left=.0
|bar1-right=.1
|bar1-colour={{period color|neoproterozoic}}

|legend2=[[Palaeozoic]]
<br />(first era of the [[Phanerozoic]])
|legend2-colour={{period color|paleozoic}}
|bar2-from=-538.8
|bar2-to=-490
|bar2-left=0
|bar2-right=.1
|bar2-colour={{period color|palaeozoic}}

<!--Periods-->
|bar3-text='''[[Cryogenian]]'''
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|bar3-colour={{period color|cryogenian}}

<!--Dividing line-->
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|bar23-left=0.1

|bar4-from=-635
|bar4-to=-538.8
|bar4-left=.1
|bar4-colour={{period color|Ediacaran}}
|bar4-border-width=.0
|bar4-text='''[[Ediacaran]]'''
|bar4-nudge-down=6.7

|bar24-from=-539.0
|bar24-to=-538.6
|bar24-colour=black

|bar5-text='''[[Cambrian]]'''
|bar5-from=-538.8
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|bar5-left=.1
|bar5-colour={{period color|cambrian}}

|bar25-from=-490.3
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<!--Organisms-->
|bar21-from=-610
|bar21-to=-555
|bar21-left=0.85
|bar21-right=0.95
|bar21-colour=#007777
|note21=''[[Aspidella]]''<br />discs
|note21-at=-585
|note21-colour=#007777
|note21-remove-arrow=yes
|note21-nudge-left=5.4

|bar22-from=-575
|bar22-to=-545
|bar22-left=0.77
|bar22-right=.87
|bar22-colour=#777700
|note22=''Charnia''
|note22-at=-560
|note22-colour=#777700
|note22-nudge-left=5.5
|note22-remove-arrow=yes

<!--Notes-->
|note1=Last Ediacaran communities
|note1-at=-538.8
|note1-colour=green

|note2=Last putative Ediacaran
|note2-at=-500
|note2-colour=green

|note3=[[Fossil embryos|Embryos]]?
|note3-at=-632.5
|note3-nudge-up=0.25
|note3-colour=green

|note4=Last [[snowball Earth|extensive]] [[glaciation]]
|note4-at=-635
|note4-nudge-down=0.5

|note5=First Ediacaran megafossil
|note5-at=-610
|note5-colour=green

|note6=[[Gaskiers glaciation (geology)|Gaskiers<br />glaciation]]
|note6-at=-584.2

|note7=[[Avalon explosion]]
|note7-at=-575

|caption=Axis scale: million years
<br />References: Waggoner (1998),<ref name=Waggoner1998t>
{{cite journal
 | last = Waggoner | first = Ben
 | year = 1998
 | title = Interpreting the earliest Metazoan fossils: What can we learn?
 | journal = [[Integrative and Comparative Biology]]
 | volume = 38 | issue = 6 | pages = 975–982
 | issn = 1540-7063
 | doi = 10.1093/icb/38.6.975 | doi-access = free
}}
</ref> Hofmann, Narbonne, & Aitken (1990)<ref>
{{cite journal
 | last1 = Hofmann  | first1 = H.J.
 | last2 = Narbonne | first2 = G.M.
 | last3 = Aitken   | first3 = J.D.
 | year=1990
 | title=Ediacaran remains from intertillite beds in northwestern Canada
 | journal=[[Geology (journal)|Geology]]
 | volume=18  | issue=12  | pages=1199–1202
 | bibcode = 1990Geo....18.1199H
 | doi=10.1130/0091-7613(1990)018<1199:ERFIBI>2.3.CO;2
}}
</ref>
}}

==History==
{{Life timeline}}
The first Ediacaran fossils discovered were the disc-shaped ''[[Aspidella]] terranovica'' in 1868. Their discoverer, Scottish geologist [[Alexander Murray (geologist)|Alexander Murray]], found them useful aids for correlating the age of rocks around [[Newfoundland (island)|Newfoundland]].<ref name=Gehling1999a /> However, since they lay below the "Primordial Strata" of the [[Cambrian]] that was then thought to contain the very first signs of animal life, a proposal four years after their discovery by [[Elkanah Billings]] that these simple forms represented fauna was dismissed by his peers. Instead, they were interpreted as [[fumarole|gas escape]] structures or inorganic [[concretion]]s.<ref name=Gehling1999a/> No similar structures elsewhere in the world were then known and the one-sided debate soon fell into obscurity.<ref name=Gehling1999a>{{cite journal|title=The First Named Ediacaran Body Fossil, ''Aspidella terranovica'' |first1=James G. |last1=Gehling |last2=Narbonne |first2=Guy M. |last3=Anderson |first3=Michael M. |year=2000 |journal=Palaeontology |volume=43 |issue=3 |page=429 |doi=10.1111/j.0031-0239.2000.00134.x |doi-access=free |bibcode=2000Palgy..43..427G }}</ref> In 1933, [[Georg Gürich]] discovered specimens in [[Namibia]] but assigned them to the Cambrian Period.<ref name=Gurich1933>{{cite journal |last=Gürich |first=G. |year=1933 |title=Die Kuibis-Fossilien der Nama-Formation von Südwestafrika | journal=Paläontologische Zeitschrift |volume=15 |issue=2–3 |pages=137–155 |language=de |doi=10.1007/bf03041648 |bibcode=1933PalZ...15..137G |s2cid=130968715 }}</ref> In 1946, [[Reg Sprigg]] noticed "jellyfishes" in the [[Ediacara Hills]] of Australia's [[Flinders Ranges]], which were at the time believed to be Early Cambrian.<ref name=Sprigg1947>{{cite journal |last=Sprigg |first=R. C. |year=1947 |title=Early Cambrian "jellyfishes" of Ediacara, South Australia and Mount John, Kimberly District, Western Australia |journal=Transactions of the Royal Society of South Australia |volume=73 |pages=72–99}}</ref>

[[File:oldest multi-cellular animal.jpg|thumb|left|Palaeontologist Guy Narbonne examining Ediacaran fossils in Newfoundland]]

It was not until the British discovery of the iconic ''[[Charnia]]'' that the [[Precambrian]] was seriously considered as containing life. This [[frond]]-shaped fossil was found in England's [[Charnwood Forest]] first by a 15&nbsp;year-old girl in 1956 ([[Tina Negus]], who was not believed<ref name=Mason-2007-Disc>{{cite web |last=Mason |first=Roger |year=2007 |title=The discovery of Charnia masoni |website=[[University of Leicester]] |url=http://www.le.ac.uk/gl/charnia2007/AbstractBooklet2007r.pdf |access-date=5 April 2016 |archive-date=8 March 2021 |archive-url=https://web.archive.org/web/20210308141852/https://www.le.ac.uk/gl/charnia2007/AbstractBooklet2007r.pdf |url-status=dead }}</ref>{{efn|
"In April 1957, I went rock-climbing in Charnwood Forest with two friends, Richard Allen and Richard Blachford ('Blach'), fellow students at Wyggeston Grammar School, Leicester. I was already interested in geology and knew that the rocks of the Charnian Supergroup were Precambrian although I had not heard of the Australian fossils.
:
Richard Allen and I agree that Blach (who died in the early 1960s) drew my attention to the leaf-like fossil holotype now on display in Leicester City Museum. I took a rubbing and showed it to my father, who was Minister of the Great Meeting Unitarian Chapel in East Bond Street, taught part-time at University College (soon to be Leicester University) and thus knew Trevor Ford. We took Trevor to visit the fossil site and convinced him that it was a genuine fossil. His publication of the discovery in the ''Journal of the Yorkshire Geological Society'' established the genus Charnia and aroused worldwide interest. ... I was able to report the discovery because of my father's encouragement and the enquiring approach fostered by my science teachers. Tina Negus saw the frond before I did but no one took her seriously."<ref name=Mason-2007-Disc/>
}}) and then the next year by a group of three schoolboys including 15&nbsp;year-old [[Roger Mason (geologist)|Roger Mason]].<ref>{{cite web |url=http://www.le.ac.uk/gl/charnia2007/Poster-flyer2007.pdf |title=Leicester's fossil celebrity: Charnia and the evolution of early life |access-date=2007-06-22 |archive-date=6 October 2022 |archive-url=https://web.archive.org/web/20221006144805/https://www.le.ac.uk/gl/charnia2007/Poster-flyer2007.pdf |url-status=dead }}</ref><ref>{{cite web |url=http://www.charnia.org.uk/newsletter/2007/discovery_charnia_2007.htm |title=The discovery of ''Charnia'' |author=Ford, Trevor |archive-url=https://web.archive.org/web/20110723120011/http://www.charnia.org.uk/newsletter/2007/discovery_charnia_2007.htm |archive-date=2011-07-23}}</ref><ref>{{cite web |title=An account of the discovery of ''Charnia'' |author=Negus, Tina |url=http://www.charnia.org.uk/newsletter/2007/discovery_charnia_2007.htm |archive-url=https://web.archive.org/web/20110723120011/http://www.charnia.org.uk/newsletter/2007/discovery_charnia_2007.htm |archive-date=2011-07-23}}</ref> Due to the detailed [[geological map]]ping of the [[British Geological Survey]], there was no doubt these fossils sat in Precambrian rocks. Palaeontologist [[Martin Glaessner]] finally, in 1959, made the connection between this and the earlier finds<ref>{{Cite journal| last=Sprigg |first=R. C.| year=1991| title=Martin F Glaessner: Palaeontologist extraordinaire| journal =Mem. Geol. Soc. India| volume =20| pages =13–20}}</ref><ref>{{cite journal | last=Glaessner |first=M.F. |author-link=Martin Glaessner | year=1959  | title=The oldest fossil faunas of South Australia | journal=International Journal of Earth Sciences | volume=47 | issue=2 | pages=522–531 | doi=10.1007/BF01800671 |bibcode=1959GeoRu..47..522G | s2cid=140615593 }}</ref> and with a combination of improved dating of existing specimens and an injection of vigour into the search, many more instances were recognised.<ref>{{cite magazine | last=Glaessner |first=Martin F. |author-link=Martin Glaessner | year=1961 | title=Precambrian animals | magazine=[[Scientific American]] | volume=204 | issue=3 | pages=72–78 | doi=10.1038/scientificamerican0361-72 | bibcode=1961SciAm.204c..72G}}</ref>

All specimens discovered until 1967 were in coarse-grained [[sandstone]] that prevented preservation of fine details, making interpretation difficult. [[Shiva Balak Misra|S.B. Misra]]'s discovery of fossiliferous [[Volcanic ash|ash]]-beds at the [[Mistaken Point]] assemblage in Newfoundland changed all this as the delicate detail preserved by the fine ash allowed the description of features that were previously undiscernible.<ref>{{Cite journal |last=Misra |first=S.B. |author-link=Shiva Balak Misra |year=1969 |title=Late Precambrian(?) fossils from southeastern Newfoundland |journal=Geol. Soc. Am. Bull. |volume=80 |issue=11 |pages=2133–2140 |doi=10.1130/0016-7606(1969)80[2133:LPFFSN]2.0.CO;2 |bibcode=1969GSAB...80.2133M }}</ref><ref>{{cite web | title=Mistaken Point fossil assemblage | department=The Miller Museum of Geology | publisher=[[Queen's University, Canada|Queen's University]] |place=Kingston, Ontario, Canada | url=http://geol.queensu.ca/museum/index.php?option=com_content&view=article&id=54&Itemid=61 | archive-url=https://archive.today/20130115133256/http://geol.queensu.ca/museum/index.php?option=com_content&view=article&id=54&Itemid=61 | archive-date=January 15, 2013}}</ref> It was also the first discovery of Ediacarans in deep water sediments.<ref>{{cite book |last1=Narbonne |first1=G.M. |year=2007 |title=The Rise of Animals |publisher=Johns Hopkins University Press |isbn=978-0-8018-8679-9 |page=55}}</ref>

Poor communication, combined with the difficulty in correlating globally distinct [[formation (geology)|formation]]s, led to a plethora of different names for the biota.
In 1960 the French name "Ediacarien" – after the Ediacara Hills – was added to the competing terms "Sinian" and "Vendian"<ref name=Termier1960>{{cite journal | last1=Termier |first1= H. | last2=Termier |first2=G. | year=1960 | title=L'Édiacarien, premier étage paléontologique | journal=Revue générale des sciences pures et appliquées | issue=3–4 | pages=175–192 | volume=67 | language = fr }}</ref> for terminal-Precambrian rocks, and these names were also applied to the life-forms. "Ediacaran" and "Ediacarian" were subsequently applied to the epoch or period of [[geologic time scale|geological time]] and its corresponding rocks. In March 2004, the [[International Union of Geological Sciences]] ended the inconsistency by formally naming the terminal [[period (geology)|period]] of the [[Neoproterozoic]] after the Australian locality.<ref name=Knoll2006>{{cite journal | last1=Knoll | first1=Andy H. | last2=Walter |first2=M. |last3=Narbonne |first3=G. |last4=Christie-Blick |first4=N. | year=2006 | title=The Ediacaran period: A new addition to the geologic time scale | journal=Lethaia | volume=39 | pages=13–30 | doi=10.1080/00241160500409223 | bibcode=2006Letha..39...13K | url=http://www.stratigraphy.org/bak/ediacaran/Knoll_et_al_2004a.pdf | archive-url=https://web.archive.org/web/20070221084915/http://geol.queensu.ca/people/narbonne/KnollWalterNarbonneChristieBlick_Lethaia_2006.pdf | archive-date=2007-02-21}}</ref>

The term "Ediacaran biota" and similar ("Ediacara" / "Ediacaran" / "Ediacarian" / "Vendian" and "fauna" / "biota") has, at various times, been used in a geographic, stratigraphic, taphonomic, or biological sense, with the latter the most common in modern literature.<ref>{{cite journal |last=MacGabhann |first= Breandán Anraoi |year=2014 |title=There is no such thing as the 'Ediacara Biota' |journal=Geosciences Frontiers |volume=5 |issue=1 |pages=53–62|doi= 10.1016/j.gsf.2013.08.001 |bibcode= 2014GeoFr...5...53M }}</ref>

==Preservation==
{{Main|Ediacaran type preservation}}

===Microbial mats===
[[Image:Cyanobacterial-algal mat.jpg|thumb|left|Modern [[cyanobacterial]]-algal mat, salty lake on the [[White Sea]] seaside]]
[[Microbial mat]]s are areas of sediment stabilised by the presence of colonies of microbes that secrete sticky fluids or otherwise bind the sediment particles. They appear to migrate upwards when covered by a thin layer of sediment but this is an illusion caused by the colony's growth; individuals do not, themselves, move. If too thick a layer of sediment is deposited before they can grow or reproduce through it, parts of the colony will die leaving behind fossils with a characteristically wrinkled ("elephant skin") and tubercular texture.<ref name=Runnegar1992>{{Cite book | last1=Runnegar |first1=B.N. | last2=Fedonkin |first2=M.A. | editor-last=Schopf |editor-first=W.J. |editor2-last=Klein |editor3-last=C. | year=1992 | chapter=Proterozoic metazoan body fossils | title=The Proterozoic Biosphere | publisher=Cambridge University Press | pages=369–388 | isbn=978-0-521-36615-1 | oclc=23583672}}</ref>

Some Ediacaran strata with the texture characteristics of microbial mats contain fossils, and Ediacaran fossils are almost always found in beds that contain these microbial mats. Although microbial mats were once widespread before the [[Cambrian substrate revolution]], the evolution of grazing organisms vastly reduced their numbers.<ref name=Zhuravlev2001>{{cite book | last1=Burzin | first1=M.B. | last2=Debrenne | first2=F. | last3=Zhuravlev | first3=A.Y. | year=2001 | chapter=Evolution of shallow-water level-bottom communities | editor-last=Zhuravlev | editor-first=A. Y. | editor2-last=Riding | editor2-first=R. | title=The Ecology of the Cambrian Radiation | publisher=Columbia University Press | location=New York, NY | isbn=978-0-231-50516-1 | oclc=51852000 | pages=216–237 | chapter-url=https://www.questia.com/PM.qst?a=o&docId=100738360 | access-date=26 August 2017 | archive-date=18 November 2007 | archive-url=https://web.archive.org/web/20071118231450/http://www.questia.com/PM.qst?a=o&docId=100738360 | url-status=dead }}</ref> These communities are now limited to inhospitable [[refugium (population biology)|refugia]], such as the [[stromatolites]] found in [[Hamelin Pool Marine Nature Reserve]] in [[Shark Bay]], [[Western Australia]], where the salt levels can be twice those of the surrounding sea.<ref>{{cite journal |last1=Burns |first1=B.P. |last2=Goh |first2=F. |last3=Allen |first3=M. |last4=Neilan |first4=B.A. |year=2004 |title=Microbial diversity of extant stromatolites in the hypersaline marine environment of Shark Bay, Australia |journal=Environmental Microbiology |volume=6 |issue=10 |pages=1096–1101 |doi=10.1111/j.1462-2920.2004.00651.x |pmid=15344935|bibcode=2004EnvMi...6.1096B }}</ref>

=== Fossilization ===

[[File:Charniodiscus.png|thumb|upright|The fossil ''[[Charniodiscus]]'' is barely distinguishable from the "elephant skin" texture on this cast.]]

The preservation of Ediacaran fossils is of interest, since as soft-bodied organisms they would normally not fossilize. Further, unlike later soft-bodied fossil biota such as the [[Burgess Shale]] or [[Solnhofen Limestone]], the Ediacaran biota is not found in a restricted environment subject to unusual local conditions: they are global. The processes that were operating must therefore have been systemic and worldwide. Something about the Ediacaran Period permitted these delicate creatures to be left behind; the fossils may have been preserved by virtue of rapid covering by ash or sand, trapping them against the mud or microbial mats on which they lived.<ref name="Narbonne1998">{{cite magazine |last=Narbonne |first=Guy M. |year=1998 |title=The Ediacara biota: A terminal Neoproterozoic experiment in the evolution of life |magazine=[[GSA Today]] |volume=8 |issue=2 |pages=1–6 |issn=1052-5173 |url=https://www.geosociety.org/gsatoday/archive/8/2/pdf/gt9802.pdf}}</ref> Their preservation was possibly enhanced by the high concentration of silica in the oceans before silica-secreting organisms such as sponges and diatoms became prevalent.<ref>{{cite journal |last1=Tarhan |first1=Lidya G. |last2=Hood |first2=Ashleigh v.S. |last3=Droser |first3=Mary L. |last4=Gehling |first4=James G. |last5=Briggs |first5=Derek E.G. |year=2016 |title=Exceptional preservation of soft-bodied Ediacara Biota promoted by silica-rich oceans |journal=Geology |volume=44 |issue=11 |page=951 |doi=10.1130/G38542.1 |bibcode=2016Geo....44..951T}}</ref> Ash beds provide more detail and can readily be dated to the nearest million years or better using [[radiometric dating]].<ref>{{cite book |last1=Bowring |first1=S.A. |last2=Martin |first2=M.W. |year=2001 |chapter=Calibration of the Fossil Record |title =Palæobiology II: A synthesis |editor1=Briggs  |editor2=Crowther |isbn=978-0-632-05149-6 |oclc=51481754 |publisher=Blackwell publishing group |chapter-url=http://www.blackwellpublishing.com/book.asp?ref=9780632051496 |access-date=2007-06-21 |archive-url=https://web.archive.org/web/20070929155954/http://www.blackwellpublishing.com/book.asp?ref=9780632051496 |archive-date=2007-09-29}}</ref> However, it is more common to find Ediacaran fossils under sandy beds deposited by storms or in [[turbidite]]s formed by high-energy bottom-scraping ocean currents.<ref name="Narbonne1998"/> Soft-bodied organisms today rarely fossilize during such events, but the presence of widespread microbial mats probably aided preservation by stabilising their impressions in the sediment below.<ref>{{Cite journal |author=Gehling, J.G. |year=1987 |title=Earliest known echinoderm – A new Ediacaran fossil from the Pound Subgroup of South Australia |journal=Alcheringa |volume=11 |issue=4 |pages=337–345 |doi=10.1080/03115518708619143|bibcode=1987Alch...11..337G }}</ref>

=== Scale of preservation ===

The rate of cementation of the overlying substrate relative to the rate of decomposition of the organism determines whether the top or bottom surface of an organism is preserved. Most disc-shaped fossils decomposed before the overlying sediment was cemented, whereupon ash or sand slumped in to fill the void, leaving a cast of the organism's underside. Conversely, [[Pneu structure|quilted fossils]] tended to decompose ''after'' the cementation of the overlying sediment; hence their upper surfaces are preserved. Their more resistant nature is reflected in the fact that, in rare occasions, quilted fossils are found ''within'' storm beds as the high-energy sedimentation did not destroy them as it would have the less-resistant discs. Further, in some cases, the [[bacteria]]l [[precipitation (chemistry)|precipitation]] of minerals formed a "death mask", ultimately leaving a positive, cast-like impression of the organism.<ref name=Gehling1999b>{{Cite journal |last=Gehling |first=J. G. |date=1999-02-01 |title=Microbial mats in terminal Proterozoic siliciclastics; Ediacaran death masks |journal=PALAIOS |volume=14 |issue=1 |pages=40–57 |url=https://pubs.geoscienceworld.org/sepm/palaios/article-abstract/14/1/40/99706/microbial-mats-in-terminal-proterozoic?redirectedFrom=fulltext |doi=10.2307/3515360 |jstor=3515360 |url-access=subscription |bibcode=1999Palai..14...40G |archive-date=28 December 2023 |access-date=8 June 2019 |archive-url=https://web.archive.org/web/20231228120756/https://pubs.geoscienceworld.org/sepm/palaios/article-abstract/14/1/40/99706/microbial-mats-in-terminal-proterozoic?redirectedFrom=fulltext |url-status=live }}</ref><ref>{{cite journal |last1=Liu |first1=Alexander G. |year=2016 |title=Framboidal pyrite shroud confirms the 'death mask' model for moldic preservation of Ediacaran soft-bodied organisms |journal=PALAIOS |volume=31 |issue=5 |pages=259–274 |bibcode=2016Palai..31..259L |doi=10.2110/palo.2015.095 |hdl=1983/535d288a-68ee-4481-8553-6b7d2e45dacb |hdl-access=free |s2cid=132601490 |url=https://research-information.bristol.ac.uk/files/67154984/Resubmission_Merged_PDF.pdf |archive-date=30 April 2019 |access-date=8 August 2018 |archive-url=https://web.archive.org/web/20190430061337/https://research-information.bristol.ac.uk/files/67154984/Resubmission_Merged_PDF.pdf |url-status=live }}</ref>

==Morphology==
{| class="wikitable floatright"
|-
! colspan="2" style="text-align:center; background:#7b7;"| Forms of Ediacaran fossil
|-
| style="width:250px;"| The earliest discovered potential embryo, preserved within an acanthomorphic [[acritarch]]. The term 'acritarch' describes a range of unclassified cell-like fossils.
| style="width:150px;"| [[File:Doushantou Embryo Yinetal2007.jpg|150px|The earliest discovered potential embryo, preserved within an acanthomorphic acritarch.]]
|-
| style="width:250px;"|''Tateana inflata'' ('''[[Cyclomedusa]]' radiata'') were originally believed to have been Medusoids, although recent research suggests that they were holdfasts of [[Petalonamae|Petalonamids]].
| style="width:150px;"|[[File:Cyclomedusa cropped.jpg|150px|''Tateana inflata'' (= '''Cyclomedusa' radiata'') is attachment disk of unknown organism]]
|-
| style="width:250px;"|A cast of ''[[Charnia]]'', the first accepted complex Precambrian organism. ''Charnia'' was once interpreted as a relative of the [[sea pen]]s.
| style="width:150px;"|[[File:Charnia Spun.jpg|150px|A cast of Charnia]]
|-
| style="width:250px;"|''[[Dickinsonia]]'' displays the characteristic quilted appearance of Ediacaran enigmata.
| style="width:150px;"|[[File:DickinsoniaCostata.jpg|150px|A cast of Dickinsonia]]
|-
| style="width:250px; vertical-align:top;"|''[[Spriggina]]'' was originally interpreted as [[annelid]] or [[arthropod]]. However, lack of known limbs, and glide reflected [[Isomer (Proarticulata)|isomers]] instead of true [[Segmentation (biology)|segments]], rejects any such classification despite some superficial resemblance.
| style="width:150px;"|[[File:Spriggina Floundensi 4.png|150px|Spriggina may be one of the predators that led to the demise of the Ediacaran fauna]]
|-
| style="width:250px;"|Late Ediacaran ''[[Archaeonassa]]''-type trace fossils are commonly preserved on the top surfaces of sandstone strata.
| style="width:150px;"|[[File:Ediacaran trace fossil.jpg|150px|Late Ediacaran Archaeonassa-type trace fossils are commonly preserved on the top surfaces of sandstone strata]]
|-
| style="width:250px;"|''[[Epibaion]] waggoneris'', chain of trace platforms and the imprint of the body of ''[[Yorgia]] waggoneri'' (right), which created these traces on microbial mat.
| style="width:150px;"|[[File:Yorgia trace.jpg|150px|''[[Yorgia]]'' chain of trace platforms terminate by the body of the animal (right).]]
|}

The Ediacaran biota exhibited a vast range of [[morphology (biology)|morphological]] characteristics. Size ranged from millimetres to metres; complexity from "blob-like" to intricate; rigidity from sturdy and resistant to jelly-soft. Almost all forms of [[symmetry (biology)#Bilateral symmetry|symmetry]] were present. These organisms differed from earlier, mainly microbial, fossils in having an organised, differentiated multicellular construction and centimetre-plus sizes.<ref name="Narbonne1998" />

These disparate morphologies can be broadly grouped into [[wastebasket taxon|form taxa]]:

; "Embryos" : Recent discoveries of Precambrian multicellular life have been dominated by reports of embryos, particularly from the [[Doushantuo Formation]] in China. Some finds<ref name="Chen2004">{{Cite journal | last1=Chen |first1=J-Y | date=Jul 2004 | title=Small Bilaterian Fossils from 40 to 55 Million Years Before the Cambrian | journal=Science | volume=305 | issue=5681 | pages=218–222 | doi=10.1126/science.1099213 | pmid=15178752 | last2=Bottjer | first2=DJ | last3=Oliveri | first3=P | last4=Dornbos | first4=SQ | last5=Gao | first5=F | last6=Ruffins | first6=S | last7=Chi | first7=H | last8=Li | first8=CW | last9=Davidson | first9=EH |s2cid=115443209 | bibcode=2004Sci...305..218C | doi-access=free }}</ref> generated intense media excitement<ref>For example, {{cite web|url=http://www.nbcnews.com/id/5112628|title=Fossil may be ancestor of most animals|access-date=2007-06-22|work=NBC News|date=2004-06-03|archive-date=23 November 2019|archive-url=https://web.archive.org/web/20191123041212/http://www.nbcnews.com/id/5112628|url-status=live}}, {{cite web|url=http://www.astrobio.net/exclusive/1005/earliest-bilateral-fossil-discovered|title=Earliest Bilateral Fossil Discovered|access-date=2007-06-22|author=Leslie Mullen|work=Astrobiology Magazine|date=2004-06-05|archive-url=https://web.archive.org/web/20110628183833/http://www.astrobio.net/exclusive/1005/earliest-bilateral-fossil-discovered|archive-date=2011-06-28|url-status=usurped}}</ref> though some have claimed they are instead inorganic structures formed by the precipitation of minerals on the inside of a hole.<ref name=BengtsonBudd2004 /> Other "embryos" have been interpreted as the remains of the giant [[sulfur]]-reducing bacteria akin to ''[[Thiomargarita]]'',<ref name=Bailey2007>e.g. {{Cite journal | last1=Bailey |first1=J. V. | last2=Joye |first2=S. B. |last3=Kalanetra |first3=K. M. |last4=Flood |first4=B. E. |last5=Corsetti |first5=F. A. | date=Jan 2007 | title=Evidence of giant sulphur bacteria in Neoproterozoic phosphorites | journal=Nature | volume=445 | issue=7124 | pages=198–201 | doi=10.1038/nature05457 | pmid=17183268 |bibcode=2007Natur.445..198B |s2cid=4346066 }}, summarised by {{Cite journal | last=Donoghue |first=P.C.J. |date=Jan 2007 | title=Embryonic identity crisis | journal=Nature | volume=445 | issue=7124 | pages=155–156 | doi=10.1038/nature05520 | pmid=17183264 |bibcode=2007Natur.445..155D |s2cid=28908035 }}</ref> a view that, while it had enjoyed a notable gain of supporters<ref name=BaileyvsXiao>Xiao ''et al.''.'s response to Bailey ''et al.''.'s original paper :<br/>
{{cite journal | last1=Xiao |first1=S. | last2=Zhou |first2=C. |last3=Yuan |first3=X. | date=Apr 2007 | title=Palaeontology: undressing and redressing Ediacaran embryos | journal=Nature | volume=446 | issue=7136 | pages=E9–E10 | doi=10.1038/nature05753 | pmid=17410133 |bibcode=2007Natur.446....9X |s2cid=4406666 }}
And Bailey ''et al.''.'s reply: {{Cite journal |author1=Bailey, J. V. |author2=Joye, S. B. |author3=Kalanetra, K. M. |author4=Flood, B. E. |author5=Corsetti, F. A. | year=2007 | title=Palaeontology: Undressing and redressing Ediacaran embryos (Reply) | journal=Nature | volume=446 | issue=7136 | pages=E10–E11 | doi=10.1038/nature05754 |bibcode=2007Natur.446...10B | s2cid=25500052 }}</ref><ref name=Knolletal2006>{{Cite journal |author1=Knoll, A. H. |author2=Javaux, E. J. |author3=Hewitt, D. |author4=Cohen, P. |date =Jun 2006 |title =Eukaryotic organisms in Proterozoic oceans |journal =Philosophical Transactions of the Royal Society B |volume =361 |issue =1470 |pages =1023–1038 |doi =10.1098/rstb.2006.1843 |pmid =16754612 |pmc =1578724}}</ref> as of 2007, has since suffered following further research comparing the potential Doushantuo embryos' morphologies with those of ''Thiomargarita'' specimens, both living and in various stages of decay.<ref>{{cite journal |first1=J.A. |last1=Cunningham |first2=C.-W. |last2=Thomas |first3=S. |last3=Bengtson |first4=F. |last4=Marone |first5=M. |last5=Stampanoni |first6=F.R. |last6=Turner |first7=J.V. |last7=Bailey |first8=R.A. |last8=Raff |first9=E.C.|last9=Raff |display-authors=6 |date=2012-05-07 |title=Experimental taphonomy of giant sulphur bacteria: implications for the interpretation of the embryo-like Ediacaran Doushantuo fossils |journal=Proceedings of the Royal Society of London B: Biological Sciences |volume=279 |issue=1734 |pages=1857–1864 |issn=0962-8452 |pmc=3297454 |pmid=22158954 |doi=10.1098/rspb.2011.2064}}</ref> A recent discovery of comparable Ediacaran fossil embryos from the Portfjeld Formation in Greenland has significantly expanded the paleogeographical occurrence of Doushantuo-type fossil "embryos" with similar biotic forms now reported from differing paleolatitudes.<ref>{{Cite journal |last1=Willman |first1=Sebastian |last2=Peel |first2=John S. |last3=Ineson |first3=Jon R. |last4=Schovsbo |first4=Niels H. |last5=Rugen |first5=Elias J. |last6=Frei|first6=Robert |display-authors=3 |date=2020-11-06 |title=Ediacaran Doushantuo-type biota discovered in Laurentia |journal=Communications Biology |volume=3 |issue=1 |page=647 |doi=10.1038/s42003-020-01381-7 |doi-access=free |pmid=33159138 |pmc=7648037 |issn=2399-3642}}</ref> 
: Microfossils dating from {{Ma|632.5}} – just 3&nbsp;million years after the end of the Cryogenian glaciations – may represent embryonic 'resting stages' in the life cycle of the earliest known animals.<ref name=Leiming2007>{{cite journal | author1=Leiming, Y. |author2=Zhu, M. |author3=Knoll, A. |author4=Yuan, X. |author5=Zhang, J. |author6= Hu, J. |display-authors=3 |date=2007-04-05 | title=Doushantuo embryos preserved inside diapause egg cysts | journal=[[Nature (journal)|Nature]] | volume=446 | issue=7136 | pages=661–663 | doi=10.1038/nature05682 | pmid=17410174 |bibcode=2007Natur.446..661Y |s2cid=4423006 }}</ref> An alternative proposal is that these structures represent adult stages of the multicellular organisms of this period.<ref name="Newman2006">{{cite journal |author1=Newman, S.A. |author2=Forgacs, G. |author3=Müller, G.B. |year=2006 |title =Before programs: The physical origination of multicellular forms |journal=Int. J. Dev. Biol. |volume=50 |issue=2–3 |pages=289–299 |doi=10.1387/ijdb.052049sn |pmid=16479496 |doi-access=free }}</ref> Microfossils of ''[[Caveasphaera]]'' are thought to foreshadow the evolutionary origin of animal-like embryology.<ref>{{cite journal |last1=Yin |first1=Zongjun |last2=Vargas |first2=Kelly |last3=Cunningham |first3=John |last4=Bengtson |first4=Stefan |last5=Zhu |first5=Maoyan |last6=Marone |first6=Federica |last7=Donoghue |first7=Donoghue |display-authors=3 |date=16 Dec 2019 |title=The Early Ediacaran Caveasphaera Foreshadows the Evolutionary Origin of Animal-like Embryology |journal=Current Biology |volume=29 |issue=24 |pages=4307–4314.e2 |doi=10.1016/j.cub.2019.10.057 |pmid=31786065 |s2cid=208332041 |doi-access=free |bibcode=2019CBio...29E4307Y |hdl=1983/13fb76e4-5d57-4e39-b222-14f8a8fae303 |hdl-access=free }}</ref>

; Discs : Circular fossils, such as ''[[Ediacaria]]'', ''[[Cyclomedusa]]'', and ''[[Rugoconites]]'' led to the initial identification of Ediacaran fossils as [[cnidaria]], which include jellyfish and corals.<ref name=Sprigg1947 /> Further examination has provided alternative interpretations of all disc-shaped fossils: not one is now confidently recognised as a jellyfish. Alternate explanations include [[holdfast (biology)|holdfast]]s and [[protist]]s;<ref name=McMenamin1998/> the patterns displayed where two meet have led to many 'individuals' being identified as microbial colonies,<ref name=Dima2001/><ref name=Grezhdankin2007>{{cite journal |author1=Grazhdankin, D. |author2=Gerdes, G. |year=2007 |title=Ediacaran microbial colonies |journal=Lethaia |volume=40 |issue=3 |pages=201–210 |doi=10.1111/j.1502-3931.2007.00025.x|bibcode=2007Letha..40..201G }}</ref> and yet others may represent scratch marks formed as stalked organisms spun around their holdfasts.<ref name=Jensen2002>{{Cite journal | last1=Jensen | first1=S. | last2=Gehling | first2=J. G. | last3=Droser | first3=M. L. | last4=Grant | first4=S. W. F. | year=2002 | title=A scratch circle origin for the medusoid fossil Kullingia | journal=Lethaia | volume=35 | issue=4 | pages=291–299 | doi=10.1080/002411602320790616 | doi-broken-date=13 May 2025 | bibcode=2002Letha..35..291J | url=http://earthsciences.ucr.edu/docs/Soren_scratch_2002.pdf | citeseerx=10.1.1.535.2625 | archive-date=3 October 2011 | access-date=8 December 2008 | archive-url=https://web.archive.org/web/20111003153554/http://earthsciences.ucr.edu/docs/Soren_scratch_2002.pdf | url-status=live }}</ref>

; Bags : Fossils such as ''[[Pteridinium]]'' preserved within sediment layers resemble "mud-filled bags". The scientific community is a long way from reaching a consensus on their interpretation.<ref name=UndergroundInNamibia>(a) The only current description, far from universal acceptance, appears as: {{cite journal |author1=Grazhdankin, D. |author2=Seilacher, A. |author2-link=Adolf Seilacher |year=2002 |title=Underground Vendobionta from Namibia |journal=Palaeontology |volume=45 |issue=1 |pages=57–78 |doi=10.1111/1475-4983.00227 |doi-access=free|bibcode=2002Palgy..45...57G }}</ref>

; Toroids : The fossil ''Vendoglossa tuberculata'' from the Nama Group, Namibia, has been interpreted as a dorso-ventrally compressed stem-group metazoan, with a large gut cavity and a transversely ridged [[ectoderm]]. The organism is in the shape of a flattened torus, with the long axis of its toroidal body running through the approximate center of the presumed gut cavity.<ref>{{Cite book |author=McMenamin, M.A.S. |author-link= Mark A. S. McMenamin |year=2009 |title=Paleotorus: The Laws of Morphogenetic Evolution |publisher=Meanma Press |isbn=978-1-893882-18-8}}</ref>

; Quilted organisms : The organisms considered in Seilacher's revised definition of the Vendobionta<ref name="Seilacher1992">{{cite journal | author=Seilacher, A. | author-link=Adolf Seilacher | year=1992 | title=Vendobionta and Psammocorallia: lost constructions of Precambrian evolution | journal=Journal of the Geological Society, London | volume=149 | issue=4 | pages=607–613 | url=http://jgs.lyellcollection.org/cgi/content/abstract/149/4/607 | doi=10.1144/gsjgs.149.4.0607 | bibcode=1992JGSoc.149..607S | s2cid=128681462 | url-access=subscription | archive-date=9 March 2009 | access-date=21 June 2007 | archive-url=https://web.archive.org/web/20090309105405/http://jgs.lyellcollection.org/cgi/content/abstract/149/4/607 | url-status=live }}</ref> share a "quilted" appearance and resembled an inflatable [[mattress]]. Sometimes these quilts would be torn or ruptured prior to preservation: Such damaged specimens provide valuable clues in the reconstruction process. For example, the three (or more) petaloid fronds of ''[[Swartpuntia]] germsi'' could only be recognised in a posthumously damaged specimen – usually multiple fronds were hidden as burial squashed the organisms flat.<ref>{{cite journal |last1=Narbonne |first1=Guy M. |last2=Saylor |first2=Beverly Z. |last3=Grotzinger |first3=John P. |year=1997 |title=The Youngest Ediacaran Fossils from Southern Africa |s2cid=28211337 |journal=[[Journal of Paleontology]] |volume=71 |issue=6 |pages=953–967 |doi= 10.1017/s0022336000035940|pmid=11541433 |jstor=1306595 |bibcode=1997JPal...71..953N }}</ref> These organisms appear to form two groups: the [[fractal]] [[rangeomorph]]s and the simpler [[erniettomorphs]].<ref name=Xiao2009>{{Cite journal| last1=Xiao| last2= Laflamme | first1=S.| first2=M. | date=January 2009 | title=On the eve of animal radiation: phylogeny, ecology and evolution of the Ediacara biota | journal=[[Trends in Ecology and Evolution]] | volume=24 | issue=1 | pages=31–40 | pmid=18952316 | doi=10.1016/j.tree.2008.07.015| bibcode= 2009TEcoE..24...31X }}</ref> Including such fossils as the iconic ''[[Charnia]]'' and ''[[Swartpuntia]]'', the group is both the most iconic of the Ediacaran biota and the most difficult to place within the existing [[tree of life]]. Lacking any mouth, gut, reproductive organs, or indeed any evidence of internal anatomy, their lifestyle was somewhat peculiar by modern standards; the most widely accepted hypothesis holds that they sucked nutrients out of the surrounding seawater by osmotrophy<ref>{{cite journal |author=McMenamin, M. |author-link=Mark A. S. McMenamin |year=1993 |title=Osmotrophy in fossil protoctists and early animals |journal=Invertebrate Reproduction and Development |volume=22 |issue=1–3 |pages=301–304}}</ref> or [[osmosis]].<ref name=Laflamme2009>{{cite journal | last1=Laflamme | first1=M. | last2=Xiao | first2=S. | last3=Kowalewski | first3=M. | year=2009 | title=Osmotrophy in modular Ediacara organisms | journal=Proceedings of the National Academy of Sciences | volume=106 | issue=34 | pages=14438–14443 | bibcode=2009PNAS..10614438L | pmid=19706530 | pmc=2732876 | doi=10.1073/pnas.0904836106 | doi-access=free }}</ref> However, others argue against this.<ref>{{cite journal | last1=Liu | first1=Alexander G. | last2=Kenchington | first2=Charlotte G. | last3=Mitchell | first3=Emily G. | year=2015 | title=Remarkable insights into the paleoecology of the Avalonian Ediacaran macrobiota | journal=Gondwana Research | volume=27 | issue=4 | pages=1355–1380 | bibcode=2015GondR..27.1355L | doi=10.1016/j.gr.2014.11.002 | doi-access=free | hdl=1983/ef181134-4023-4747-8137-ed9da7a97771 | hdl-access=free }}</ref>

; Non-Vendobionts 

: Possible [[stem group|early forms]] of [[Extant taxon|living]] [[phylum|phyla]], excluding them from some definitions of the Ediacaran biota. The earliest such fossil is the reputed bilaterian ''[[Vernanimalcula]]'' claimed by some, however, to represent the infilling of an egg-sac or [[acritarch]].<ref name=BengtsonBudd2004>{{cite journal |last1=Bengtson |first1=S. |last2=Budd |first2=G. |date=19 November 2004 |title=Comment on "Small bilaterian fossils from 40 to 55&nbsp;million years before the Cambrian" |journal=[[Science (journal)|Science]] |volume=306 |issue=5700 |page=1291 |doi=10.1126/science.1101338 |doi-access=free |pmid=15550644}}</ref><ref name="Chen, et al.2004">{{Cite journal|journal=Science |date=19 November 2004 |volume=306 |page=1291 |doi=10.1126/science.1102328 |title=Response to Comment on "Small Bilaterian Fossils from 40 to 55 Million Years Before the Cambrian" |author=Chen, J.-Y. |issue=5700 |pmid=15550644 |doi-access=free }}</ref> In 2020, ''[[Ikaria wariootia]]'' was claimed to represent one of the oldest organisms with anterior and posterior differentiation.<ref>{{Cite journal |last1=Evans |first1=Scott D. |last2=Hughes |first2=Ian V. |last3=Gehling |first3=James G. |last4=Droser |first4=Mary L. |date=2020-04-07 |title=Discovery of the oldest bilaterian from the Ediacaran of South Australia |journal=Proceedings of the National Academy of Sciences |volume=117 |issue=14 |pages=7845–7850 |doi=10.1073/pnas.2001045117  |doi-access=free |issn=0027-8424 |pmid=32205432 |pmc=7149385 |bibcode=2020PNAS..117.7845E}}</ref> Later examples are almost universally accepted as bilaterians and include the mollusc-like ''[[Kimberella]]'',<ref name=Fedonkin1997>{{Cite journal | author=Fedonkin, M.A. |author2=Waggoner, B.M. |date=Nov 1997 | title=The Late Precambrian fossil Kimberella is a mollusc-like bilaterian organism | journal=Nature | volume=388 | issue=6645 | pages=868–871 | doi=10.1038/42242 | bibcode=1997Natur.388..868F|s2cid=4395089 | doi-access=free }}</ref> ''[[Spriggina]]'' (pictured)<ref name=McMenamin2003>{{cite conference | first=M.A.S. | last=McMenamin | author-link=Mark A. S. McMenamin | year=2003 | title=''Spriggina'' is a Trilobitoid Ecdysozoan | conference=Seattle Annual Meeting of the GSA | url=http://gsa.confex.com/gsa/2003AM/finalprogram/abstract_62056.htm | access-date=2007-06-21 | archive-date=30 August 2008 | archive-url=https://web.archive.org/web/20080830080220/http://gsa.confex.com/gsa/2003AM/finalprogram/abstract_62056.htm | url-status=dead }}</ref> and the shield-shaped ''[[Parvancorina]]''<ref>{{cite journal | author=Glaessner, M.F. | year=1980 | title=''Parvancorina'' – an arthropod from the late Precambrian of South Australia | journal=Ann. Nat. Hist. Mus. Wien. | volume=83 | pages=83–90 }}</ref> whose affinities are currently debated.<ref>For a reinterpretation, see {{cite journal |author1=Ivantsov, A.Y. |author2=Malakhovskaya, Y.E. |author3=Serezhnikova, E.A. |year=2004 |title=Some problematic fossils from the Vendian of the southeastern White Sea region |journal=[[Paleontological Journal]] |volume=38 |issue=1 |pages=1–9 |url=http://www.vend.paleo.ru/pub/Ivantsov_et_al_2004_eng.pdf |access-date=2007-06-21 |archive-url=https://web.archive.org/web/20070704183946/http://www.vend.paleo.ru/pub/Ivantsov_et_al_2004_eng.pdf |archive-date=2007-07-04}}</ref> A suite of fossils known as the [[small shelly fossil]]s are represented in the Ediacaran, most famously by ''[[Cloudinid|Cloudina]]''<ref name=Germs1972>{{cite journal | author=Germs, G.J.B. | date=October 1972 | title=New shelly fossils from Nama Group, South West Africa | journal=[[American Journal of Science]] | volume=272 | issue=8 | pages=752–761 | url=http://www.ajsonline.org/cgi/reprint/272/8/752 | doi=10.2475/ajs.272.8.752 | bibcode=1972AmJS..272..752G | url-access=subscription | archive-date=27 September 2007 | access-date=21 June 2007 | archive-url=https://web.archive.org/web/20070927005047/http://www.ajsonline.org/cgi/reprint/272/8/752 | url-status=live }}</ref> a shelly tube-like fossil that often shows evidence of predatory boring, suggesting that, while predation may not have been common in the Ediacaran Period, it was at least present.<ref name="Hua2003BoringsInCloudinaShells">{{Cite journal |author = Hua, H. |author2=Pratt, B.R. |author3=Zhang, L.U.Y.I. | year = 2003 | journal = PALAIOS | title = Borings in Cloudina Shells: Complex Predator-Prey Dynamics in the Terminal Neoproterozoic | doi = 10.1669/0883-1351(2003)018<0454:BICSCP>2.0.CO;2 | volume = 18 | issn = 0883-1351 | issue = 4–5 |page=454 |bibcode=2003Palai..18..454H |s2cid=131590949 }}</ref><ref name="Bengtson1992PredatorialBorings">{{cite journal | author = Bengtson, S. |author2=Zhao, Y. | date = 1992-07-17 | title = Predatorial Borings in Late Precambrian Mineralized Exoskeletons | journal = Science | volume = 257 | issue = 5068 | pages = 367–9 | doi = 10.1126/science.257.5068.367 | pmid = 17832833 |bibcode = 1992Sci...257..367B |s2cid=6710335 }}</ref> Organic microfossils known as [[small carbonaceous fossil]]s are found in Ediacaran sediments, including the spiral-shaped ''[[Cochleatina]]'' which spans the Ediacaran–Cambrian boundary.<ref>{{Cite journal |last1=Slater |first1=Ben J.|last2=Harvey |first2=Thomas H. P. |last3=Bekker |first3=Andrey |last4=Butterfield |first4=Nicholas J. |year=2020 |title=Cochleatina: An enigmatic Ediacaran–Cambrian survivor among small carbonaceous fossils (SCFs)|journal=Palaeontology |volume=63 |issue=5 |pages=733–752 |issn=1475-4983 |doi=10.1111/pala.12484 |doi-access=free |bibcode=2020Palgy..63..733S }}</ref> ''Ediacaria'' also survived well into the Cambrian. Representatives of modern taxa existed in the Ediacaran, some of which are recognisable today. [[Sponge]]s, red and green [[alga|algæ]], [[protist]]s and [[bacteria]] are all easily recognisable with some pre-dating the Ediacaran by nearly three billion years. Possible arthropods have also been described.<ref name=Ivantsov2006>{{cite conference |author =Ivantsov A.Yu. |date=17–21 July 2006 |title=New find of Cambrian type arthropoda from the Vendian of the White Sea, Russia |conference=The Second International Palaeontological Congress |place=Beijing, China |type=abstract |url=http://www.igcp512.org/documents/IPC-T2-Abstracts.pdf |archive-url=https://web.archive.org/web/20090225144529/http://www.igcp512.org/documents/IPC-T2-Abstracts.pdf |archive-date=2009-02-25}}</ref> Surface trails left by ''[[Treptichnus]]'' bear similarities to modern [[Priapulida|priapulids]]. Fossils of the hard-shelled [[foraminifera]] ''[[Platysolenites]]'' are known from the latest Ediacaran of western [[Siberia]], coexisting with ''Cloudina'' and ''[[Namacalathus]]''.<ref>{{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) |journal=Russian Geology and Geophysics |lang=en |volume=49 |issue=12 |pages=932–939 |doi=10.1016/j.rgg.2008.06.012 |issn=1068-7971 |bibcode=2008RuGG...49..932K |url=http://www.sciencedirect.com/science/article/pii/S106879710800206X|url-access=subscription }}</ref>

; Filaments
: Filament-shaped structures in Precambrian fossils have been observed on many occasions. [[Frondose]] fossils in Newfoundland have been observed to have developed filamentous bedding planes, inferred to be [[stolon]]ic outgrowths.<ref>{{cite journal |last1=Liu |first1=Alexander G. |last2=Dunn |first2=Frances S. |date=2020-04-06 |title=Filamentous Connections between Ediacaran Fronds |journal=[[Current Biology]] |language=English |volume=30 |issue=7 |pages=1322–1328.e3 |doi=10.1016/j.cub.2020.01.052 |doi-access=free |issn=0960-9822 |pmid=32142705|bibcode=2020CBio...30E1322L }}</ref> A study of Brazilian Ediacaran fossils found filamentous microfossils, suggested to be eukaryotes or large [[Microbial metabolism|sulfur-oxidizing-bacteria]] (SOBs).<ref>{{Cite journal|last1=Becker-Kerber|first1=Bruno|last2=de Barros|first2=Gabriel Eduardo Baréa|last3=Paim|first3=Paulo Sergio Gomes|last4=Prado|first4=Gustavo M. E. M.|last5=da Rosa|first5=Ana Lucia Zucatti|last6=El Albani|first6=Abderrazak|last7=Laflamme|first7=Marc|date=2021-01-13|title=In situ filamentous communities from the Ediacaran (approx. 563 Ma) of Brazil|url= |journal=Proceedings of the Royal Society B: Biological Sciences |volume=288 |issue=1942 |page=20202618 |doi=10.1098/rspb.2020.2618 |pmc=7892400 |pmid=33402067}}</ref> Fungus-like filaments found in the Doushantuo Formation have been interpreted as eukaryotes and possibly fungi, providing possible evidence for the evolution and terrestrialization of fungi ~635 Ma.<ref>{{Cite journal |last1=Gan |first1=Tian |last2=Luo |first2=Taiyi |last3=Pang |first3=Ke |last4=Zhou |first4=Chuanming |last5=Zhou |first5=Guanghong |last6=Wan |first6=Bin |last7=Li |first7=Gang |last8=Yi|first8=Qiru |last9=Czaja |first9=Andrew D. |last10=Xiao |first10=Shuhai |display-authors=6 |date=2021-01-28|title=Cryptic terrestrial fungus-like fossils of the early Ediacaran Period |journal=Nature Communications |lang=en |volume=12 |issue=1 |pages=641 |doi=10.1038/s41467-021-20975-1 |doi-access=free |pmid=33510166 |pmc=7843733 |bibcode=2021NatCo..12..641G |issn=2041-1723}}</ref>

; [[Trace fossil]]s : With the exception of some very simple [[Skolithos|vertical burrows]]<ref name=Fedonkin_1985>{{Cite book |first=M.A. |last=Fedonkin |year=1985 |chapter=Paleoichnology of Vendian Metazoa |editor1=Sokolov, B.S. |editor2=Iwanowski, A.B. |title=Vendian System: Historical–Geological and Paleontological Foundation |location=Moscow, RU |publisher=Nauka |volume=1&nbsp;Paleontology |pages=112–116 |language=ru}}</ref> the only Ediacaran burrows are horizontal, lying on or just below the surface of the seafloor. Such burrows have been taken to imply the presence of motile organisms with heads, which would probably have had a bilateral symmetry. This could place them in the [[bilateria|bilateral]] [[clade]] of [[animal]]s<ref>{{Cite book | author=Fedonkin, M.A. | year=1992 | chapter= Vendian faunas and the early evolution of Metazoa | title=Origin and early evolution of the Metazoa | editor=Lipps, J.H. | editor2=Signor, P.W. | pages=87–129 | isbn=978-0-306-44067-0 | publisher=Plenum | chapter-url=https://books.google.com/books?id=gUQMKiJOj64C&pg=PP1 | access-date=2007-03-08}}</ref> but they could also have been made by simpler organisms feeding as they slowly rolled along the sea floor.<ref name=Matz2008>{{cite journal |last1=Matz |first1=V. |last2=Frank |first2=M. |last3=Marshall |first3=J. |first4=A. |last5=Johnsen |first5=S. |date=Dec 2008 |title=Giant deep-sea protist produces bilaterian-like traces |journal=[[Current Biology]] |volume=18 |issue=23 |pages=1849–1854 |issn=0960-9822 |pmid=19026540| last4=Widder| doi=10.1016/j.cub.2008.10.028 |s2cid=8819675 |doi-access=free|bibcode=2008CBio...18.1849M }}</ref> Putative "burrows" dating as far back as {{Ma|1100|million&nbsp;years}} may have been made by animals that fed on the undersides of microbial mats, which would have shielded them from a chemically unpleasant ocean;<ref name=Seilacher1998>{{Cite journal | author=Seilacher, A. | author-link=Adolf Seilacher | author2=Bose, P.K. |author3=Pflüger, F. | date=1998-10-02 | title=Triploblastic animals more than 1&nbsp;billion years ago: Trace fossil evidence from India | journal=[[Science (journal)|Science]] | volume=282 | issue=5386 | pages=80–83 | doi=10.1126/science.282.5386.80 | pmid=9756480 |bibcode=1998Sci...282...80S }}</ref> however their uneven width and tapering ends make a biological origin so difficult to defend<ref name=Budd2000>{{Cite journal | author=Budd, G. E. | author2=Jensen, S. | year=2000 | title=A critical reappraisal of the fossil record of the bilaterian phyla | journal=Biological Reviews | volume=75 | issue=2 | pages=253–295 | doi=10.1111/j.1469-185X.1999.tb00046.x | url=http://www.journals.cambridge.org/abstract_S000632310000548X | access-date=2007-06-27 | pmid=10881389 | s2cid=39772232 | archive-date=15 September 2019 | archive-url=https://web.archive.org/web/20190915160434/https://www.cambridge.org/core/journals/biological-reviews/article/critical-reappraisal-of-the-fossil-record-of-the-bilaterian-phyla/84D1DF6738A47E565B400A50590E15E2 | url-status=dead | url-access=subscription }}</ref> that even the original proponent no longer believes they are authentic.<ref>{{Cite journal | doi=10.1126/science.1166220 | title=Paleontology: Reading Behavior from the Rocks | year=2008 | author=Jensen, S. | journal=Science | volume=322 | issue=5904 | pages=1051–1052 | s2cid=129734373 }}</ref>

: The burrows observed imply simple behaviour, and the complex efficient feeding traces common from the start of the Cambrian are absent. Some Ediacaran fossils, especially discs, have been interpreted tentatively as trace fossils but this hypothesis has not gained widespread acceptance. As well as burrows, some trace fossils have been found directly associated with an Ediacaran fossil. ''[[Yorgia]]'' and ''[[Dickinsonia]]'' are often found at the end of [[fossil trackway|long pathway]]s of trace fossils matching their shape;<ref name=Ivantsov2002>{{Cite journal |author =Ivantsov, A. Y. |author2 =Malakhovskaya, Y. E. |year =2002 |title =Giant Traces of Vendian Animals |journal =Doklady Earth Sciences |volume =385 |issue =6 |pages =618–622 |language =ru |url =http://vend.paleo.ru/pub/Ivantsov_et_Malakhovskaya_2002-e.pdf |archive-url =https://web.archive.org/web/20070704183947/http://vend.paleo.ru/pub/Ivantsov_et_Malakhovskaya_2002-e.pdf |archive-date=2007-07-04}}</ref> these fossils are thought to be associated with [[cilium|ciliary]] feeding but the precise method of formation of these disconnected and overlapping fossils largely remains a mystery.<ref name=Oslo_2008>{{cite conference |first=A.Yu. |last=Ivantsov |year=2008 |url=http://www.cprm.gov.br/33IGC/1323085.html |title=Feeding traces of the Ediacaran animals |series=HPF-17 Trace fossils : Ichnological concepts and methods |conference=International Geological Congress |place=Oslo |access-date=7 July 2009 |archive-date=18 January 2020 |archive-url=https://web.archive.org/web/20200118235203/http://www.cprm.gov.br/33IGC/1323085.html |url-status=dead }}</ref> The potential [[mollusc]] ''Kimberella'' is associated with scratch marks, perhaps formed by a [[radula]].<ref name=Fedonkin2007>According to<br/>
{{The Rise and Fall of the Ediacaran Biota |author=Fedonkin, M.A. |author2=Simonetta, A |author3=Ivantsov, A.Y. |chapter=New data on ''Kimberella'', the Vendian mollusc-like organism (White sea region, Russia): palaeoecological and evolutionary implications |pages=157–179 |doi=10.1144/SP286.12}}
:
For a more cynical perspective see<br/>
{{Cite journal |last=Butterfield |first=N.J. |date=Dec 2006 |title=Hooking some stem-group "worms": Fossil lophotrochozoans in the Burgess Shale |journal=BioEssays |volume=28 |issue=12 |pages=1161–1166 |issn=0265-9247 |pmid=17120226 |doi=10.1002/bies.20507 |s2cid=29130876}}
</ref>

==Classification and interpretation==
[[File:Diorama of the Ediacaran biota at the Field Museum in Chicago.jpg|thumb|A reconstruction of the Ediacaran biota at the [[Field Museum of Natural History|Field Museum]] in Chicago]]
Classification of the Ediacarans is inevitably difficult, hence a variety of theories exist as to their placement on the tree of life.

[[Martin Glaessner]] proposed in ''The Dawn of Animal Life'' (1984) that the Ediacaran biota were recognizable [[crown group]] members of modern phyla, but were unfamiliar because they had yet to evolve the characteristic features we use in modern classification.<ref name=Glaessner1984>{{Cite book | title=The Dawn of Animal Life: A Biohistorical Study | author=Glaessner, M. F. | year=1984 | isbn=978-0-521-31216-5 | publisher=Cambridge University Press | oclc=9394425 | url-access=registration | url=https://archive.org/details/dawnofanimallife0000glae }}</ref>

In 1998 [[Mark A. S. McMenamin|Mark McMenamin]] claimed Ediacarans did not possess an [[embryo]]nic stage, and thus could not be animals. He believed that they independently evolved a [[nervous system]] and [[brain]]s, meaning that "the path toward intelligent life was embarked upon more than once on this planet".<ref name=McMenamin1998/>

In 2018 analysis of ancient [[sterol]]s was taken as evidence that one of the period's most-prominent and iconic fossils, ''[[Dickinsonia]]'', was an early animal.<ref name=Bobrov-Hope-etal-2018/>

=== Cnidarians ===

[[File:Virgularia sp. (Purple sea pen).jpg|upright|thumb|A [[sea pen]], a modern cnidarian bearing a passing resemblance to ''[[Charnia]]'']]

Since the most primitive [[eumetazoans]]—multi-cellular animals with tissues—are [[cnidarians]], and the first recognized Ediacaran fossil ''[[Charnia]]'' looks very much like a [[sea pen]], the first attempt to categorise these fossils designated them as [[jellyfish]] and [[sea pen]]s.<ref>{{Cite journal |author1=Donovan, Stephen K. |author2=Lewis, David N. |year=2001 |title=Fossils explained 35. The Ediacaran biota |journal=Geology Today |volume=17 |issue =3 |pages=115–120 |doi=10.1046/j.0266-6979.2001.00285.x |s2cid=128395097 }}</ref> However, more recent discoveries have established that many of the circular forms formerly considered "cnidarian medusa" are actually holdfasts – sand-filled vesicles occurring at the base of the stem of upright frond-like Ediacarans. A notable example is the form known as ''[[Charniodiscus]]'', a circular impression later found to be attached to the long 'stem' of a frond-like organism that now bears the name.<ref>{{cite journal |last=Ford |first=T.D. |year=1958 |title=The Pre-cambrian fossils of Charnwood Forest |journal=Proceedings of the Yorkshire Geological Society |volume=31 |issue=3 |pages=211–217 |doi=10.1144/pygs.31.3.211 |bibcode=1958PYGS...31..211F }}</ref><ref>Discussed at length in {{cite journal |last1=Laflamme |first1=M. |last2=Narbonne |first2=G. M. |last3=Anderson |first3=M. M. |year=2004 |title=Morphometric analysis of the Ediacaran frond ''Charniodiscus'' from the Mistaken Point Formation, Newfoundland |journal=Journal of Paleontology |volume=78 |issue=5 |pages=827–837 |doi=10.1666/0022-3360(2004)078<0827:MAOTEF>2.0.CO;2 |bibcode=2004JPal...78..827L |citeseerx=10.1.1.544.5084 |s2cid=85862666 }}</ref>

The link between frond-like Ediacarans and sea pens has been thrown into doubt by multiple lines of evidence; chiefly the derived nature of the most frond-like pennatulacean octocorals, their absence from the fossil record before the Tertiary, and the apparent cohesion between segments in Ediacaran frond-like organisms.<ref>{{cite journal |last=Williams |first=G.C. |year=1997 |title=Preliminary assessment of the phylogenetics of pennatulacean octocorals, with a reevaluation of Ediacaran frond-like fossils, and a synthesis of the history of evolutionary thought regarding the sea pens |journal=Proceedings of the Sixth International Conference of Coelenterate Biology |pages=497–509}}</ref> Some researchers have suggested that an analysis of "growth poles" discredits the pennatulacean nature of Ediacaran fronds.<ref>{{Cite journal |last1=Antcliffe |first1=J. B. |author2=Brasier, M. D. |year=2007 |title=Charnia and sea pens are poles apart |journal=Journal of the Geological Society |volume=164 |issue=1 |pages=49–51 |doi=10.1144/0016-76492006-080 |url=http://jgs.geoscienceworld.org/cgi/reprint/164/1/49 |bibcode=2007JGSoc.164...49A |s2cid=130602154 |url-access=subscription |archive-date=23 August 2007 |access-date=9 April 2007 |archive-url=https://web.archive.org/web/20070823001601/http://jgs.geoscienceworld.org/cgi/reprint/164/1/49 |url-status=live }}</ref><ref name=Antcliffe2007>{{Cite journal |last1=Antcliffe |first1=J. B.  |author2=Brasier, M. D. |year=2007 |title=Charnia At 50: Developmental Models For Ediacaran Fronds |journal=Palaeontology |volume=51 |issue=1 |pages=11–26 |doi=10.1111/j.1475-4983.2007.00738.x |s2cid=83486435 |doi-access=free }}</ref>

===Protozoans===

[[File:xenophyophore.jpg|thumb|right|A single-celled xenophyophore in the [[Galapagos Rift]]]]

[[Adolf Seilacher]] has suggested that in the Ediacaran, animals take over from giant [[protist]]s as the dominant life form.<ref>{{Cite journal |last1=Seilacher |first1=Adolf |author1-link=Adolf Seilacher |author2=Grazhdankin, D. |author3=Legouta, A. |year=2003 |title=Ediacaran biota: The dawn of animal life in the shadow of giant protists |journal=Paleontological Research |volume=7 |issue=1 |pages=43–54 |doi=10.2517/prpsj.7.43 |doi-access=free |bibcode=2003PalRe...7...43S |url=https://ci.nii.ac.jp/naid/110002695304/ |archive-date=5 August 2020 |access-date=13 June 2025 |archive-url=https://web.archive.org/web/20200805094835/https://ci.nii.ac.jp/naid/110002695304/ |url-status=live }}</ref> The modern [[xenophyophore]]s are giant single-celled protozoans found throughout the world's oceans, largely on the [[abyssal plain]]. Genomic evidence suggests that the xenophyophores are a specialised group of [[Foraminifera]].<ref>{{cite journal |last1=Pawlowski |first1=J. |last2=Holzmann |first2=M. |last3=Fahrni |first3=J. |last4=Richardson |first4=S.L. |date=2003 |title=Small subunit ribosomal DNA suggests that the xenophyophorean Syringammina corbicula isa Foraminiferan |url=https://www.scopus.com/record/display.url?eid=2-s2.0-0346965975&origin=inward&txGid=F4CB51D4D3484F134ACC334A40E7CEFF.aqHV0EoE4xlIF3hgVWgA%3a2 |journal=Journal of Eukaryotic Microbiology |volume=50 |issue=6 |pages=483–487 |doi=10.1111/j.1550-7408.2003.tb00275.x |pmid=14733441 |s2cid=39906626|url-access=subscription }}</ref>

=== Unique phyla ===

Seilacher has suggested that the Ediacaran organisms represented a unique and extinct grouping of related forms descended from a common ancestor ([[clade]]) and created the [[kingdom (biology)|kingdom]] Vendozoa,<ref>{{Cite book |last=Seilacher |first=Adolf |author-link=Adolf Seilacher |year=1984 |chapter=Late Precambrian and early Cambrian metazoa: Preservational or real extinctions? |title=Patterns of Change in Earth Evolution |editor1=Holland, H.D. |editor2=Trendall, A.F. |pages=159–168 |isbn=978-0-387-12749-1 |location=Heidelberg, Germany |publisher=Springer-Verlag |oclc=11202424}}</ref><ref name=Seilacher1989>{{cite journal |last=Seilacher |first=Adolf |author-link=Adolf Seilacher |year=1989 |title=Vendozoa: Organismic construction in the Proterozoic biosphere |journal=Lethaia |volume=17 |issue=3 |pages=229–239 |doi=10.1111/j.1502-3931.1989.tb01332.x|bibcode=1989Letha..22..229S }}</ref> named after the now-obsolete [[Vendian]] era. He later excluded fossils identified as [[metazoa]]ns and relaunched the [[phylum (biology)|phylum]] "Vendobionta", which he described as "quilted" [[cnidarians]] lacking [[cnidocyte|stinging cell]]s. This absence precludes the current cnidarian method of feeding, so Seilacher suggested that the organisms may have survived by [[symbiosis]] with [[photosynthesis|photosynthetic]] or [[chemoautotrophic]] organisms.<ref>{{cite journal |last1=Buss |first1=L.W. |last2=Seilacher |first2=Adolf |author2-link=Adolf Seilacher |year=1994 |title=The phylum Vendobionta: A sister group of the Eumetazoa? |journal=Paleobiology |volume=20 |issue=1 |pages=1–4 |doi=10.1017/S0094837300011088|jstor=2401145 |bibcode=1994Pbio...20....1B |s2cid=89131248 }}</ref> [[Mark A. S. McMenamin|Mark McMenamin]] saw such feeding strategies as characteristic for the entire biota, and referred to the marine biota of this period as a "Garden of Ediacara".<ref>{{cite journal |last=McMenamin |first=Mark A.S. |author-link= Mark A. S. McMenamin |year=1986 |title=The Garden of Ediacara |journal=PALAIOS |volume=1 |issue=2 |pages=178–182 |doi=10.2307/3514512|jstor=3514512 |bibcode=1986Palai...1..178M }}</ref>

===Lichen hypothesis===
[[File:Ediacaran petrography.jpg|thumb|Greg Retallack's analysis of thin sections and substrates of a variety of Ediacaran fossils.<ref name="Retallack2016b"/> His findings have been disputed by other scientists.<ref name="Jones 2013"/><ref name="Xiao 2013"/><ref name="Switek 2012"/>]]

[[Greg Retallack]] has proposed that Ediacaran organisms were [[lichen]]s.<ref>{{Cite journal |last=Retallack |first=G. J. |year =1994 |title=Were the Ediacaran fossils lichens? |journal =Paleobiology |volume =20 |issue =4 |pages =523–544 |access-date =2007-03-08 |url =http://www.uoregon.edu/~gregr/Papers/fossil%20lichens.pdf |archive-url =https://web.archive.org/web/20090225144529/http://www.uoregon.edu/~gregr/Papers/fossil%20lichens.pdf |archive-date=2009-02-25|doi =10.1017/S0094837300012975 |bibcode=1994Pbio...20..523R |s2cid =129180481 }}</ref><ref name="Retallack2013">{{Cite journal | author=Retallack, G. J. | year=2013 | title=Ediacaran life on land | journal=Nature | volume=493 | issue=7430 | pages=89–92 | doi=10.1038/nature11777|bibcode=2013Natur.493...89R | pmid=23235827| s2cid=205232092 }}</ref> He argues that thin sections of Ediacaran fossils show lichen-like compartments and [[hypha]]-like wisps of ferruginized clay,<ref name="Retallack2016b">{{Cite journal |last=Retallack |first=G. J. | year=2016 | title=Ediacaran fossils in thin section | journal=Alcheringa | volume=40 | issue=4 | pages=583–600 | doi=10.1080/03115518.2016.1159412|bibcode=2016Alch...40..583R | s2cid=132274535 }}</ref> and that Ediacaran fossils have been found in strata that he interprets as desert soils.<ref name="Retallack2013"/><ref>{{Cite journal  |last=Retallack |first=G. J.  | year=2012 | title=Were Ediacaran siliciclastics of South Australia coastal or deep marine? | journal=Sedimentology | volume=59 | issue=4 | pages=1208–1236 | doi=10.1111/j.1365-3091.2011.01302.x |s2cid=129547681 |bibcode=2012Sedim..59.1208R }}</ref>

The suggestion has been disputed by other scientists; some have described the evidence as ambiguous and unconvincing, for instance noting that ''Dickinsonia'' fossils have been found on rippled surfaces (suggesting a marine environment), while trace fossils like ''Radulichnus'' could not have been caused by needle ice as Retallack has proposed.<ref name="Jones 2013">{{cite journal | title=Soil or sea for ancient fossils | last=Jones |first=Nicola | journal=Nature Geoscience | date=February 2013 | volume=6 | page=84 | bibcode=2013NatGe...6...84J | doi=10.1038/ngeo1713 | issue=2 | doi-access=free }}</ref><ref name="Xiao 2013">{{cite journal | title=Muddying the waters | last=Xiao |first=Shuhai H. |journal=Nature | year=2013 | volume=493 | pages=28–29 | doi=10.1038/nature11765 | pmid=23235825 | issue=7430 | doi-access=free }}</ref><ref name="Switek 2012">{{cite journal |last=Switek |first=Brian |title=Controversial claim puts life on land 65 million years early |journal=Nature |date=12 December 2012 |doi=10.1038/nature.2012.12017 |s2cid=130305901 |url=https://www.nature.com/news/controversial-claim-puts-life-on-land-65-million-years-early-1.12017 |access-date=19 November 2013|url-access=subscription }}</ref> Ben Waggoner notes that the suggestion would place the root of the [[Cnidaria]] back from around 900 mya to between 1500 mya and 2000 mya, contradicting much other evidence.<ref name=Waggoner1995>{{Cite journal | last=Waggoner | first=B. M. | year=1995 | title=Ediacaran Lichens: A Critique | journal=Paleobiology | volume=21 | issue=3 | pages=393–397 | doi = 10.1017/S0094837300013373 | jstor=2401174 | bibcode=1995Pbio...21..393W | s2cid=82550765 }}</ref><ref name=Waggoner2004>{{Cite journal | last1=Waggoner |first1=Ben M. |last2=Collins |first2=Allen G. | year=2004 | title=''Reductio Ad Absurdum'': Testing The Evolutionary Relationships Of Ediacaran And Paleozoic Problematic Fossils Using Molecular Divergence Dates | journal=Journal of Paleontology | volume=78 | issue=1 | pages=51–61 | doi=10.1666/0022-3360(2004)078<0051:RAATTE>2.0.CO;2 |bibcode=2004JPal...78...51W |s2cid=8556856 |url=https://repository.si.edu/bitstream/handle/10088/21610/iz_Waggoner_Collins_JP2004.pdf }}</ref> Matthew Nelsen, examining phylogenies of [[Ascomycota|ascomycete]] fungi and [[Chlorophyta|chlorophyte]] algae (components of lichens), calibrated for time, finds no support for the hypothesis that lichens predated the [[vascular plant]]s.<ref>{{Cite journal | last=Nelsen |first=Matthew P. | year=2019 | title=No support for the emergence of lichens prior to the evolution of vascular plants | journal=Geobiology | volume=18 | issue=1 | pages=3–13 | doi=10.1111/gbi.12369 | pmid=31729136 |bibcode=2020Gbio...18....3N | doi-access=free }}</ref>

===Other interpretations===
Several classifications have been used to accommodate the Ediacaran biota at some point,<ref name="Waggoner1998">{{cite journal |author=Waggoner, Ben |year=1998 |title=Interpreting the earliest metazoan fossils: What can we learn? |journal=Integrative and Comparative Biology |volume=38 |issue=6 |pages=975–982 |doi=10.1093/icb/38.6.975 |doi-access =free }}</ref> from [[algae]],<ref>{{Cite journal | author=Ford, T.D. | year=1958 | title=Pre-Cambrian fossils from Charnwood Forest | journal=Proceedings of the Yorkshire Geological Society | volume=31 | issue=6 | pages=211–217 | doi=10.1046/j.1365-2451.1999.00007.x| s2cid=130109200 }}</ref> to [[protozoans]],<ref>{{cite conference | author=Zhuralev | year=1992 | title=Were Vend-Ediacaran multicellulars metazoa? | conference=29th International Geological Congress |place=Kyoto, Japan | volume=2 | page=339 }}</ref> to [[fungi]]<ref>{{Cite journal |author1=Peterson, K.J. |author2= Waggoner B. |author3=Hagadorn, J.W. | year=2003 | title=A fungal analog for Newfoundland Ediacaran fossils? | journal=[[Integrative and Comparative Biology]] | volume=43 | issue=1 | pages=127–136 | doi=10.1093/icb/43.1.127 | pmid=21680417 | doi-access=free }}</ref> to [[bacteria]]l or [[microbe|microbial]] colonies,<ref name=Dima2001>{{cite conference | author=Grazhdankin, D. |date=5–8 November 2001 | title=Microbial origin of some of the Ediacaran fossils | conference=GSA Annual Meeting | pages=177 | url=http://gsa.confex.com/gsa/2001AM/finalprogram/abstract_21602.htm | access-date=2007-03-08 | archive-url=https://web.archive.org/web/20140911063210/https://gsa.confex.com/gsa/2001AM/finalprogram/abstract_21602.htm | archive-date=2014-09-11}}</ref> to hypothetical intermediates between plants and animals.<ref name=Pflug>{{cite journal | author=Pflug | year=1973 | title=Zur fauna der Nama-Schichten in Südwest-Afrika. IV. Mikroscopische anatomie der petalo-organisme | journal=Palaeontographica | issue=B144 | pages=166–202 | lang=de}}</ref>

A new extant genus discovered in 2014, ''[[Dendrogramma]]'', which at the time of discovery appeared to be a [[basal metazoan]] but of unknown taxonomic placement, had been noted to have similarities with the Ediacaran fauna.<ref name=jko>{{cite journal |last1=Just |first1=J. |last2=Kristensen |first2=R. M. |last3=Olesen |first3=J. |year=2014 |title=''Dendrogramma'', new genus, with two new non-bilaterian species from the marine bathyal of southeastern Australia (Animalia, Metazoa ''incertae sedis'') – with similarities to some medusoids from the Precambrian Ediacara |journal=PLOS ONE |volume=9 |issue=9 |page = e102976 |doi=10.1371/journal.pone.0102976 |doi-access=free |bibcode=2014PLoSO...9j2976J |pmid=25184248 |pmc=4153628}}</ref> It has since been found to be a [[siphonophore]], possibly even sections of a more complex species.<ref>Gough, Myles (7 June 2016). "Origin of mystery deep-sea mushroom revealed". BBC News. Retrieved 7 June 2016.</ref>

== Origin ==

It took almost 4&nbsp;billion years from the formation of the Earth for Ediacaran fossils to first appear, 655&nbsp;million years ago. While putative fossils are reported from {{Ma|3460}},<ref name=Schopf1987>{{Cite journal |author=Schopf, J. W. |author2=Packer, B. M. |date=1987-07-03 |title=Early Archean (3.3-billion to 3.5-billion-year-old) microfossils from Warrawoona Group, Australia |journal=Science |volume=237 |issue=4810 |pages=70–73 |doi=10.1126/science.11539686 |url=http://www.sciencemag.org/cgi/content/abstract/237/4810/70 |access-date=2007-05-21 |pmid=11539686 |bibcode=1987Sci...237...70S |url-access=subscription |archive-date=1 October 2007 |archive-url=https://web.archive.org/web/20071001105323/http://www.sciencemag.org/cgi/content/abstract/237/4810/70 |url-status=live }}</ref><ref name=Hofmann1999>{{Cite journal |author1=Hofmann, H. J. |author2=Grey, K. |author3=Hickman, A. H. |author4=Thorpe, R. I. |date=1999-08-01 |title=Origin of 3.45 Ga coniform stromatolites in Warrawoona Group, Western Australia |journal=Bulletin of the Geological Society of America |volume=111 |issue=8 |pages=1256–1262 |doi=10.1130/0016-7606(1999)111<1256:OOGCSI>2.3.CO;2 |bibcode=1999GSAB..111.1256H }}</ref> the first uncontroversial evidence for life is found {{Ma|2700}},<ref name=Archer2006>{{Cite journal |author=Archer, C. |author2=Vance, D. |date=2006-03-01 |title=Coupled Fe and S isotope evidence for Archean microbial Fe (III) and sulfate reduction |journal=Geology |volume=34 |issue=3 |pages=153–156 |doi=10.1130/G22067.1 |bibcode=2006Geo....34..153A }}</ref> and cells with nuclei certainly existed by {{Ma|1200}}.<ref name=Butterfield2000>{{cite journal |author=Butterfield, Nicholas J. |year=2000 |title=''Bangiomorpha pubescens'' n. gen., n. sp.: implications for the evolution of sex, multicellularity, and the Mesoproterozoic/Neoproterozoic radiation of eukaryotes |journal=Paleobiology |volume=26 |issue=3 |pages=386–404 |s2cid=36648568 |doi=10.1666/0094-8373(2000)026<0386:BPNGNS>2.0.CO;2 |bibcode=2000Pbio...26..386B |url=https://www.bioone.org/doi/pdf/10.1017/jpa.2016.124 |url-access=subscription }}</ref>

It could be that no special explanation is required: the slow process of evolution simply required 4 billion years to accumulate the necessary adaptations. Indeed, there does seem to be a slow increase in the maximum level of complexity seen over this time, with more and more [[evolution of complexity|complex forms of life evolving]] as time progresses, with traces of earlier semi-complex life such as ''[[Nimbia occlusa|Nimbia]]'', found in the {{Ma|610|million year old}} Twitya formation,<ref name=Fedonkin1980>{{Cite journal |author=Fedonkin, M. A. |year=1980 |title=New representatives of the Precambrian coelenterates in the northern Russian platform |journal=Paleontologicheskii Zhurnal |issn=0031-031X |pages=7–15 |language=ru}}</ref> and older rocks dating to {{Ma|770}} in Kazakhstan.<ref name="Meert2010">{{cite journal |last1=Meert |first1=J.G. |last2=Gibsher |first2=A.S. |last3=Levashova |first3=N.M. |last4=Grice |first4=W.C. |last5=Kamenov |first5=G.D. |last6=Rybanin |first6=A. |year=2010 |title=Glaciation and ~770 Ma Ediacara (?) Fossils from the Lesser Karatau Microcontinent, Kazakhstan |journal=Gondwana Research |volume=19 |issue=4 |pages=867–880 |doi=10.1016/j.gr.2010.11.008 |bibcode=2011GondR..19..867M }}</ref> 

[[File:AntarcticaDomeCSnow.jpg|thumb|Global [[ice sheet]]s might have delayed or prevented the establishment of multicellular life.]]

On the early Earth, reactive elements, such as [[iron]] and [[uranium]], existed in a [[redox|reduced]] form that would react with any free oxygen produced by [[photosynthesis]]ing organisms. Oxygen would not be able to build up in the [[atmosphere]] until all the iron had rusted (producing [[banded iron formation]]s), and all the other reactive elements had been oxidised. [[Donald Canfield]] detected records of the first significant quantities of atmospheric oxygen just before the first Ediacaran fossils appeared<ref name=Canfield1996>{{Cite journal |last1=Canfield |first1=D.E. |author2=Teske, A. |date=July 1996 |title=Late Proterozoic rise in atmospheric oxygen concentration inferred from phylogenetic and sulphur-isotope studies |journal=Nature |volume=382 |issue=6587 |pages=127–132 |doi=10.1038/382127a0 |pmid=11536736 |bibcode=1996Natur.382..127C |s2cid=4360682 }}</ref> – and the presence of atmospheric oxygen was soon heralded as a possible trigger for the Ediacaran [[adaptive radiation|radiation]].<ref name=Canfield2007>{{Cite journal |last1=Canfield |first1=D.E. |author2=Poulton, S.W. |author3=Narbonne, G.M. |date=2007-01-05 |title=Late-Neoproterozoic Deep-Ocean Oxygenation and the Rise of Animal Life |journal=Science |volume=315 |issue=5808 |pages=92–95 |pmid=17158290 |bibcode=2007Sci...315...92C |doi=10.1126/science.1135013 |s2cid=24761414|doi-access=free }}</ref> Oxygen seems to have accumulated in two pulses; the rise of small, sessile (stationary) organisms seems to correlate with an early oxygenation event, with larger and mobile organisms appearing around the second pulse of oxygenation.<ref name=Fike2006>{{cite journal |last1=Fike |first1=D.A. |author2=Grotzinger, J. P. |author3=Pratt, L.M. |author4=Summons, R.E. |date=December 2006 |title=Oxidation of the Ediacaran ocean |journal=Nature |volume=444 |issue=7120 |pages=744–7 |doi=10.1038/nature05345 |pmid=17151665 |bibcode=2006Natur.444..744F |s2cid=4337003 |url=https://authors.library.caltech.edu/36885/7/nature05345-s1.doc }}</ref> However, the assumptions underlying the reconstruction of atmospheric composition have attracted some criticism, with widespread anoxia having little effect on life where it occurs in the Early Cambrian and the Cretaceous.<ref name=Butterfield2009>{{Cite journal |last1=Butterfield |first1=N.J. |year=2009 |title=Oxygen, animals and oceanic ventilation: An alternative view |journal=Geobiology |volume=7 |issue=1 |pages=1–7 |pmid=19200141  |s2cid=31074331 |doi=10.1111/j.1472-4669.2009.00188.x|bibcode=2009Gbio....7....1B }}</ref>

[[Glacial period|Periods of intense cold]] have also been suggested as a barrier to the evolution of multicellular life.
The earliest known embryos, from China's [[Doushantuo Formation]], appear just a million years after the Earth emerged from a [[Snowball Earth|global glaciation]], suggesting that ice cover and cold oceans may have prevented the emergence of multicellular life.<ref>{{cite conference |author=Narbonne, Guy M. |date=September 2003 |chapter=Life after Snowball: The Mistaken Point biota and the origin of animal ecosystems |conference=Seattle Annual Meeting of the GSA |title=Geological Society of America Abstracts with Programs |volume=35 |issue=6 |page=516 |chapter-url=http://gsa.confex.com/gsa/2003AM/finalprogram/abstract_57850.htm |access-date=2007-06-22 |archive-url=https://web.archive.org/web/20120206215600/http://gsa.confex.com/gsa/2003AM/finalprogram/abstract_57850.htm |archive-date=2012-02-06}}</ref> 

In early 2008, a team analysed the range of basic body structures ("disparity") of Ediacaran organisms from three different fossil beds: Avalon in Canada, {{ma|575}} to {{ma|565}}; White Sea in Russia, {{ma|560}} to {{ma|550}}; and Nama in Namibia, {{ma|550}} to {{ma|542}}, immediately before the start of the Cambrian. They found that, while the White Sea assemblage had the most species, there was no significant difference in disparity between the three groups, and concluded that before the beginning of the Avalon timespan these organisms must have gone through their own evolutionary "explosion", which may have been similar to the famous [[Cambrian explosion]].<ref>{{Cite journal|title=The Avalon Explosion: Evolution of Ediacara Morphospace |date=4 January 2008 |volume=319|issue=5859 |pages=81–84 |doi=10.1126/science.1150279 |author=Shen, B. |author2=Dong, L. |author3=Xiao, S. |author4=Kowalewski, M. |journal=Science |pmid=18174439 |department=Science |bibcode=2008Sci...319...81S |s2cid=206509488 }}</ref>

=== Preservation bias ===

The paucity of Ediacaran fossils after the Cambrian could simply be due to conditions no longer favoring the fossilization of Ediacaran organisms, which may have continued to thrive unpreserved for a considerable time.<ref name=Runnegar1992/> However, if they were common, more than the occasional specimen<ref name=ConwayMorris1993>{{Cite journal |last=Conway Morris |first=Simon |author-link=Simon Conway Morris |year=1993 |title=Ediacaran-like fossils in Cambrian Burgess Shale–type faunas of North America |journal=Palaeontology |volume=36 |issue=31–0239 |pages=593–635}}</ref><ref>{{Cite journal |last1=Jensen |first1=S.R. |last2=Gehling |first2=J.G. |last3=Droser |first3=M. L. |year=1998 |title=Ediacara-type fossils in Cambrian sediments |journal=Nature |volume=393 |issue=6685 |pages=567–569 |doi=10.1038/31215 |bibcode=1998Natur.393..567J |s2cid=205001064|hdl=10662/19945 |hdl-access=free }}</ref> might be expected in exceptionally [[taphonomy|preserved fossil]] assemblages (Konservat-[[Lagerstatten|Lagerstätten]]) such as the [[Burgess Shale]] and [[Maotianshan shales|Chengjiang]].<ref name=Shu>{{Cite journal |author1=Shu, D.-G |author2=Conway Morris, S. |author2-link=Simon Conway Morris |author3=Han, J |author4=Li, Y |author5=Zhang, X.-L. |author6=Hua, H |author7=Zhang, Z.-F. |author8=Liu, J.-N. |author9=Guo, J.-F. |author10=Yasui, K. |author11=Yao, Y. |display-authors=3 |date=2006-05-05 |title=Lower Cambrian Vendobionts from China and Early Diploblast Evolution |journal=Science |volume=312 |issue=5774 |pages=731–4 |doi=10.1126/science.1124565 |url=http://science-mag.aaas.org/cgi/content/abstract/312/5774/731 |pmid=16675697 |bibcode=2006Sci...312..731S |s2cid=1235914 |url-access=subscription |archive-date=18 November 2007 |access-date=28 April 2007 |archive-url=https://web.archive.org/web/20071118222057/http://science-mag.aaas.org/cgi/content/abstract/312/5774/731 |url-status=live }}</ref> Although no reports of Ediacara-type organisms in the Cambrian period are widely accepted at present, a few disputed reports have been made, as well as unpublished observations of 'vendobiont' fossils from 535&nbsp;Ma Orsten-type deposits in China.<ref>{{Cite conference|title=Dwarfed vendobionts from the Cambrian Kuanchuanpu Formation in South China|url=https://www.researchgate.net/publication/305402705}}</ref>

=== Predation and grazing ===

[[File:Kimberella crop.jpg|thumb|''[[Kimberella]]'' might have had a predatory or grazing lifestyle.]]

It has been suggested that by the Early Cambrian, organisms higher in the [[trophic level|food chain]] caused the microbial mats to largely disappear. If these grazers first appeared as the Ediacaran biota started to decline, then it may suggest that they destabilised the microbial mats in a "[[Cambrian substrate revolution]]", leading to displacement or detachment of the biota; or that the destruction of the microbial [[substrate (marine biology)|substrate]] destabilized the ecosystem, causing extinctions.<ref name="BottjerEtAl2000CambrianSubstrateRevolution">{{cite magazine |last1=Bottjer |first1=D.J. |author2=Hagadorn, J.W. |author3=Dornbos, S.Q. |title=The Cambrian substrate revolution |magazine=GSA Today |volume=10 |issue=9 |date=September 2000 |url=https://www.geosociety.org/gsatoday/archive/10/9/pdf/i1052-5173-10-9-1.pdf |access-date=2008-06-28 |pages=1–9 |archive-date=7 October 2022 |archive-url=https://web.archive.org/web/20221007115106/https://www.geosociety.org/gsatoday/archive/10/9/pdf/i1052-5173-10-9-1.pdf |url-status=live }}</ref><ref name=Seilacher1994>{{cite book |last1=Seilacher |first1=Adolf |author1-link=Adolf Seilacher |last2=Pflüger |first2=F. |year=1994 |chapter=From biomats to benthic agriculture: A biohistoric revolution |editor-last=Krumbein |editor-first=W. E. |editor2-last=Peterson |editor2-first=D. M. |editor3-last=Stal |editor3-first=L. J. |title=Biostabilization of Sediments |publisher=Bibliotheks-und Informationssystem der Carl von Ossietzky Universität Oldenburg |pages=97–105 |isbn=3-8142-0483-2 }}</ref>

Alternatively, skeletonized animals could have fed directly on the relatively undefended Ediacaran biota.<ref name=McMenamin1998>{{cite book |last=McMenamin |first=M. |author-link=Mark A. S. McMenamin |year=1998 |title=The Garden of Ediacara |location=New York, NY |publisher=Columbia University Press |isbn=978-0-231-10559-0 |oclc=228271905}}</ref>
However, if the interpretation of the Ediacaran age ''[[Kimberella]]'' as a grazer is correct then this suggests that the biota had already had limited exposure to "predation".<ref name=Fedonkin1997/>

=== Competition ===

[[File:Waptia.jpg|thumb|Cambrian animals such as ''[[Waptia]]'' might have competed with, or fed upon, Ediacaran life-forms.]]

Increased competition due to the evolution of key innovations among other groups, perhaps as a response to predation, may have driven the Ediacaran biota from their niches.<ref name="Stanley1973">{{Cite journal |last=Stanley |first=S. M. |year=1973 |title=An ecological theory for the sudden origin of multicellular life in the Late Precambrian |journal=PNAS |volume=70 |issue=5 |pages=1486–1489 |pmid=16592084 |doi=10.1073/pnas.70.5.1486 |pmc=433525 |bibcode=1973PNAS...70.1486S |doi-access=free }}</ref> However, the supposed "competitive exclusion" of [[brachiopod]]s by [[Bivalvia|bivalve molluscs]] was eventually deemed to be a coincidental result of two unrelated trends.<ref>{{Cite journal |last1=Gould |first1=Stephen J. |author-link=Stephen Jay Gould |author2=Calloway, C.B. |year=1980 |title=Clams and brachiopods – ships that pass in the night |journal=Paleobiology |volume=6 |issue=4 |pages=383–396 |jstor=2400538 |doi=10.1017/s0094837300003572 |bibcode=1980Pbio....6..383G |s2cid=132467749 }}</ref>

=== Change in environmental conditions ===

Great changes were happening at the end of the Precambrian and the start of the Early Cambrian. The breakup of the [[Rodinia|supercontinent]]s,<ref>{{Cite journal |last1=McKerrow |first1=W.S. |author2=Scotese, C.R. |author3=Brasier, M.D. |year=1992 |title=Early Cambrian continental reconstructions |journal=Journal of the Geological Society, London |volume=149 |issue=4 |pages=599–606 |doi=10.1144/gsjgs.149.4.0599 |bibcode=1992JGSoc.149..599M |s2cid=129389099 }}</ref> rising sea levels (creating shallow, "life-friendly" seas),<ref>{{Cite journal |author=Hallam, A. |author-link=Anthony Hallam |year=1984 |title=Pre-Quaternary sea-level changes |journal=Annual Review of Earth and Planetary Sciences |volume=12 |pages=205–243 |doi=10.1146/annurev.ea.12.050184.001225 |bibcode=1984AREPS..12..205H }}</ref> a nutrient crisis,<ref name=Brasier1992a>{{Cite journal |author=Brasier, M.D. |year=1992 |title=Background to the Cambrian explosion |journal=Journal of the Geological Society, London |volume=149 |issue=4 |pages=585–587 |doi=10.1144/gsjgs.149.4.0585 |bibcode=1992JGSoc.149..585B |s2cid=129794777 }}</ref> fluctuations in atmospheric composition, including oxygen and carbon dioxide levels,<ref name=Brasier1992b>{{Cite journal |last=Brasier |first=M.D. |year=1992 |title=Global ocean-atmosphere change across the Precambrian-Cambrian transition |journal=Geological Magazine |volume=129 |issue=2 |pages=161–168 |doi=10.1017/S0016756800008256 |bibcode=1992GeoM..129..161B |s2cid=140652883 }}</ref> and changes in [[ocean chemistry]]<ref name=Lowenstein2001>{{cite journal |last1=Lowenstein |first1=T.K. |author2=Timofeeff, M.N. |author3=Brennan, S.T. |author4=Hardie, L.A. |author5=Demicco, R.V. |year=2001 |title=Oscillations in Phanerozoic Seawater Chemistry: Evidence from Fluid Inclusions |journal=Science |volume=294 |issue=5544 |pages=1086–1089 |pmid=11691988  |s2cid=2680231 |doi=10.1126/science.1064280 |bibcode=2001Sci...294.1086L }}</ref> (promoting [[biomineralisation]]) could all have played a part.<ref>{{Cite journal |last1=Bartley |first1=J.K. |author2=Pope, M. |author3=Knoll, A.H. |author4=Semikhatov, M. A. |author5=Petrov, P.Y.U. |year=1998 |title=A Vendian-Cambrian boundary succession from the northwestern margin of the Siberian Platform: stratigraphy, palaeontology, chemostratigraphy and correlation |journal=Geological Magazine |volume=135 |issue=4 |pages=473–494 |doi=10.1144/gsjgs.155.6.0957 |pmid=11542817 |bibcode=1998JGSoc.155..957P |s2cid=129884125 }}</ref>

==Assemblages==
Late Ediacaran macrofossils are recognized globally in at least 52 formations and a variety of [[deposition (geology)|depositional]] conditions.<ref name=Evans2022>{{Cite journal |last1=Evans |first1=Scott D. |last2=Tu |first2=Chenyi |last3=Rizzo |first3=Adriana |last4=Surprenant |first4=Rachel L. |last5=Boan |first5=Phillip C. |last6=McCandless |first6=Heather |last7=Marshall |first7=Nathan |last8=Xiao |first8=Shuhai |last9=Droser |first9=Mary L. |date=15 November 2022 |title=Environmental drivers of the first major animal extinction across the Ediacaran White Sea-Nama transition |journal=Proceedings of the National Academy of Sciences |language=en |volume=119 |issue=46 |pages=e2207475119 |doi=10.1073/pnas.2207475119 |doi-access=free |issn=0027-8424 |pmc=9674242 |pmid=36343248|bibcode=2022PNAS..11907475E }}</ref> Each formation is commonly grouped into three main types, known as [[Faunal assemblage|assemblages]] and named after typical localities. Each assemblage tends to occupy its own time period and region of morphospace, and after an initial burst of diversification (or extinction) changes little for the rest of its existence.<ref name=Erwin2008/>

{{Ediacaran assemblages graphical timeline}}

===Avalon assemblage===
{{main|Avalon assemblage}}
The Avalon assemblage is defined at [[Mistaken Point]] one the [[Avalon Peninsula]] of Canada, the oldest locality with a large quantity of Ediacaran fossils.<ref>{{cite book | author=Benus | date=May 1988 | title=Trace fossils, small shelly fossils and the Precambrian-Cambrian boundary | volume=463 | pages=81 | publisher=University of the State of New York | isbn=978-1-55557-178-8 }}</ref>
The assemblage is easily dated because it contains many fine ash-beds, which are a good source of [[zircon]]s used in the uranium-lead method of [[radiometric dating]]. These fine-grained ash beds also preserve exquisite detail. Constituents of this biota appear to survive through until the extinction of all Ediacarans at the base of the Cambrian.<ref name=Erwin2008>{{Cite journal | author=Erwin, Douglas H. |date=May 2008 | title=Wonderful Ediacarans, Wonderful Cnidarians? | journal=Evolution & Development | volume=10 | issue=3 | pages=263–264 | doi=10.1111/j.1525-142X.2008.00234.x | pmid=18460087|s2cid=205674433 }}</ref>

One interpretation of the biota is as deep-sea-dwelling [[rangeomorph]]s<ref>{{Cite journal | author=Clapham, Matthew E. | author2=Narbonne, Guy M. | author3=Gehling, James G. | year=2003 | title=Paleoecology of the oldest known animal communities: Ediacaran assemblages at Mistaken Point, Newfoundland | journal=Paleobiology | volume=29 | issue=4 | pages=527–544 | doi=10.1666/0094-8373(2003)029<0527:POTOKA>2.0.CO;2 | bibcode=2003Pbio...29..527C | s2cid=45514650 | url=http://paleobiol.geoscienceworld.org/cgi/content/abstract/29/4/527 | url-access=subscription | archive-date=23 November 2007 | access-date=22 June 2007 | archive-url=https://web.archive.org/web/20071123215731/http://paleobiol.geoscienceworld.org/cgi/content/abstract/29/4/527 | url-status=live }}</ref> such as ''[[Charnia]]'', all of which share a [[fractal]] growth pattern. They were probably preserved ''in situ'' (without post-mortem transportation), although this point is not universally accepted. The assemblage, while less diverse than the White Sea or Nama assemblages, resembles [[Carboniferous]] suspension-feeding communities, which may suggest [[filter feeder|filter feeding]] as the assemblage is often found in water too deep for photosynthesis.<ref>{{cite journal| author=Clapham, M.E. |author2=Narbonne, G.M. | year=2002| volume=30| issue=7| pages=627–630| doi=10.1130/0091-7613(2002)030<0627:EET>2.0.CO;2| journal=Geology | title=Ediacaran epifaunal tiering |bibcode=2002Geo....30..627C }}</ref>

===White Sea assemblage===
{{main|White Sea assemblage}}
The White Sea or Ediacaran assemblage is named after Russia's [[White Sea]] or Australia's [[Ediacara Hills]] and is marked by much higher diversity than the Avalon or Nama assemblages.<ref name=Evans2022/> In Australia, they are typically found in red gypsiferous and calcareous paleosols formed on [[loess]] and flood deposits in an arid cool temperate paleoclimate.<ref name=Retallack2013/> Most fossils are preserved as imprints in microbial beds,<ref>{{cite report | author=Retallack G. J. | year=2012 | title=Criteria for distinguishing microbial mats and earths |series=Special Paper | volume=101 | pages=136–152 | publisher=Society of Economic Paleontologists and Mineralogists |location=Tulsa}}</ref> but a few are preserved ''within'' sandy units.<ref name=Grazhdankin2004>{{Cite journal | author=Grazhdankin, Dima | year=2004 | title=Patterns of distribution in the Ediacaran biotas: facies versus biogeography and evolution | journal=[[Paleobiology (journal)|Paleobiology]] | volume=30 | issue=2 | pages=203–221 | doi=10.1666/0094-8373(2004)030<0203:PODITE>2.0.CO;2 | bibcode=2004Pbio...30..203G | s2cid=129376371 | url=http://paleobiol.geoscienceworld.org/cgi/reprint/30/2/203.pdf | archive-date=26 July 2011 | access-date=10 April 2007 | archive-url=https://web.archive.org/web/20110726092936/http://paleobiol.geoscienceworld.org/cgi/reprint/30/2/203.pdf | url-status=live }} (Source of data for Timeline synthesis, p. 218. Further citations available in caption to Fig. 8.)</ref><ref name=Erwin2008/>

===Nama assemblage===
{{main|Nama assemblage}}
The Nama assemblage is best represented in [[Namibia]]. It is marked by extreme biotic turnover, with rates of extinction exceeding rates of origination for the whole period.<ref name=Evans2022/> Three-dimensional preservation is most common, with organisms preserved in sandy beds containing internal bedding. Dima Grazhdankin believes that these fossils represent burrowing organisms,<ref name=UndergroundInNamibia /> while Guy Narbonne maintains they were surface dwellers.<ref>{{cite journal | last=Narbonne | first=Guy M. |year=2005 |title=The Ediacara biota: Neoproterozoic origin of animals and their ecosystems |journal=Annual Review of Earth and Planetary Sciences |volume=33 | pages=421–442 |doi=10.1146/annurev.earth.33.092203.122519 |url=http://geol.queensu.ca/people/narbonne/NarbonneAREPS2005Final.pdf |via=[[Queen's University, Canada]] |access-date=2009-01-03 |bibcode=2005AREPS..33..421N |archive-url=https://web.archive.org/web/20070221084932/http://geol.queensu.ca/people/narbonne/NarbonneAREPS2005Final.pdf |archive-date=2007-02-21
}}</ref> These beds are sandwiched between units comprising interbedded sandstones, siltstones and [[shale]]s—with microbial mats, where present, usually containing the fossils. The environment is interpreted as [[sand bar]]s formed at the mouth of a [[river delta|delta]]'s [[distributary|distributaries]].<ref name=Grazhdankin2004/> Mattress-like vendobionts (''[[Ernietta]]'', ''[[Pteridinium]]'', ''[[Rangea]]'') in these sandstones form a very different assemblage from vermiform fossils (''[[Cloudina]]'', ''[[Namacalathus]]'') of Ediacaran "wormworld" in marine [[Dolomite (rock)|dolomite]] of Namibia.<ref>{{cite magazine |last=Schiffbauer |first=J.F. |year=2016 |title=The Latest Ediacaran Wormworld Fauna: Setting the Ecological Stage for the Cambrian Explosion |s2cid=52204161 |volume=26 |issue=11 |pages=4–11 |magazine=[[GSA Today]] |doi=10.1130/GSATG265A.1 |hdl=1807/77824 |hdl-access=free }}</ref>

=== Significance of assemblages ===

Since they are globally distributed – described on all continents except [[Antarctica]] – geographical boundaries do not appear to be a factor;<ref>{{cite journal |last1=Waggoner |first1=Ben |year=1999 |title=Biogeographic analyses of the Ediacara biota: A conflict with paleotectonic reconstructions |journal=[[Paleobiology (journal)|Paleobiology]] |volume=25 |issue=4 |pages=440–458 |doi=10.1017/S0094837300020315 |jstor=2666048 |bibcode=1999Pbio...25..440W |s2cid=130817983 }}</ref> the same fossils are found at all palaeolatitudes (the latitude where the fossil was created, accounting for [[continental drift]] - an application of [[paleomagnetism]]) and in separate [[sedimentary basin]]s.<ref name=Grazhdankin2004/> An analysis of one of the White Sea fossil beds, where the layers cycle from continental seabed to inter-tidal to estuarine and back again a few times, found that a specific set of Ediacaran organisms was associated with each environment.<ref name="Grazhdankin2004"/> However, while there is some delineation in organisms adapted to different environments, the three assemblages are more distinct temporally than paleoenvironmentally.<ref>{{Cite journal |last1=Boag |first1=Thomas H. |last2=Darroch |first2=Simon A.F. |last3=Laflamme|first3=Marc|year=2016 |title=Ediacaran distributions in space and time: testing assemblage concepts of earliest macroscopic body fossils |journal=[[Paleobiology (journal)|Paleobiology]] |volume=42 |issue=4 |pages=574–594 |doi=10.1017/pab.2016.20|bibcode=2016Pbio...42..574B }}</ref> Because of this, the three assemblages are often separated by temporal boundaries rather than environmental ones (timeline at right).

As the Ediacaran biota represent an early stage in multicellular life's history, it is unsurprising that not all possible [[guild (ecology)|modes of life]] are occupied. It has been estimated that of 92 potentially possible modes of life – combinations of feeding style, tiering and motility — no more than a dozen are occupied by the end of the Ediacaran. Just four are represented in the Avalon assemblage.<ref name=Bambach2007>{{cite journal |last1=Bambach |first1=R.K. |author2=Bush, A.M. |author3=Erwin, D.H. |year=2007 |title=Autecology and the filling of Ecospace: Key metazoan radiations |journal=Palæontology |volume=50 |issue=1 |pages=1–22 |doi=10.1111/j.1475-4983.2006.00611.x |doi-access=free |bibcode=2007Palgy..50....1B }}</ref>

==See also==
{{commons category|Ediacaran biota}}
* [[Cambrian explosion]]
* [[Large ornamented Ediacaran microfossil]]
* [[List of Ediacaran genera]]
* [[Abiogenesis]]
* [[Huainan biota]]
* [[Francevillian biota]], another, much earlier [[Precambrian]] possibly pluricellular biota.

==Notes==
{{notelist}}

==References==
{{reflist|25em}}

==Further reading==
* {{Cite book|title=Palæobiology II: A synthesis |editor=[[Derek Briggs]] |editor2=Peter Crowther |isbn=978-0-632-05147-2 |year=2001 |pages=Chapter 1 |publisher=Blackwell Science |location=Malden, MA |oclc=43945263}} — Excellent further reading for the keen – includes many interesting chapters with macroevolutionary theme.
* {{cite book |author=McMenamin, M.A.S. |author-link=Mark A. S. McMenamin |year=1998 |title=The Garden of Ediacara: Discovering the first complex life |isbn=978-0-231-10558-3 |publisher=Columbia University Press |location=New York |oclc=3758852}} — A popular science account of these fossils, with a particular focus on the [[Namibian]] fossils.
* {{cite magazine |author-link=Rachel Wood (geologist) |last=Wood |first=R.A. |date=June 2019 |title=The rise of animals: New fossils and analyses of ancient ocean chemistry reveal the surprisingly deep roots of the [[Cambrian explosion]] |magazine=[[Scientific American]] |volume=320 |issue=6 |pages=24–31}}

==External links==
* {{cite news |first=Traci |last=Watson |date=28 October 2020 |title=These bizarre ancient species are rewriting animal evolution |journal=[[Nature (journal)|Nature]] |department=News |type=review |url=https://www.nature.com/articles/d41586-020-02985-z |access-date=2022-12-18 |quote=Early fossils with guts, segmented bodies and other sophisticated features reveal a revolution in animal life – before the Cambrian explosion.}} — Ediacaran biota review article, with nice illustrations
* {{cite web |title=The Ediacaran assemblage |year=2010 |website=peripatus.gen.nz |url=http://www.peripatus.gen.nz/paleontology/Ediacara.html |archive-url=https://web.archive.org/web/20101010035019/http://www.peripatus.gen.nz/paleontology/Ediacara.html |archive-date=2010-10-10}} — Thorough, though slightly out-of-date, description 
* {{cite web |title=Database of Ediacaran biota |date=July 2010 |website=complex-life.org |url=http://www.complex-life.org/database |archive-url=https://web.archive.org/web/20110725191154/http://www.complex-life.org/database |archive-date=2011-07-25}} — compilation up to 7/2010
*  {{cite web |title=The oldest complex animal fossils |year=2007 |publisher=[[Queen's University, Canada|Queen's University]] |place=Kingston, Ontario |url=http://geol.queensu.ca/museum/exhibits/ediac/drook |archive-url=https://web.archive.org/web/20070528175308/http://geol.queensu.ca/museum/exhibits/ediac/drook/ |archive-date=2007-05-28}}
* {{cite web |title=Ediacaran fossils of Canada |year=2007 |publisher=[[Queen's University, Canada|Queen's University]] |place=Kingston, Ontario |url=http://geol.queensu.ca/museum/exhibits/ediac/ediac.html |archive-url=https://web.archive.org/web/20070405091608/http://geol.queensu.ca/museum/exhibits/ediac/ediac.html |archive-date=2007-04-05}} 
* {{cite news |title=Earth's oldest animal ecosystem held in fossils at Nilpena Station in SA outback |date=5 August 2013 |publisher=[[ABC News (Australia)|ABC News]] |url=https://www.abc.net.au/news/2013-08-03/sa-pastoral-property-nilpena-holds-animal-fossils/4862432 |access-date=6 August 2013}}
* {{cite AV media |title=Meet the fossils |series=''[[Landline (TV series)|Landline]]'' |date=3 August 2013 |medium=TV program audio & transcript |publisher=[[Australian Broadcasting Corporation]] |url=https://www.abc.net.au/tv/programs/landline/old-site/content/2013/s3817544.htm |access-date=28 December 2018}} — ABC TV show on Ediacaran fossils at Nilpena
{{Spoken Wikipedia|Ediacara biota.ogg|date=2009-08-29}}
* {{In Our Time| Ediacara Biota|b00lh2s3|Ediacara_Biota}}, 2009, radio program

{{DEFAULTSORT:Ediacaran biota}}
[[Category:Ediacaran life| ]]
[[Category:Ediacaran|Biota]]
[[Category:Proterozoic life]]
[[Category:Precambrian paleobiotas]]