Editing Cloudinidae

{{Short description|Group of extinct aquatic animals}}
{{automatic taxobox
| fossil_range = {{Fossil range |555|529|refs=<ref name="Yang2016">{{cite journal|doi=10.1016/j.precamres.2016.09.016|title=Transitional Ediacaran–Cambrian small skeletal fossil assemblages from South China and Kazakhstan: Implications for chronostratigraphy and metazoan evolution|journal=Precambrian Research|volume=285|pages=202–215|year=2016|last1=Yang|first1=Ben|last2=Steiner|first2=Michael|last3=Zhu|first3=Maoyan|last4=Li|first4=Guoxiang|last5=Liu|first5=Jianni|last6=Liu|first6=Pengju|bibcode=2016PreR..285..202Y}}</ref>}}
| image = Cloudina.svg
| image_upright = 0.5
| taxon = Cloudinidae
| authority = Hahn and Pflug, 1985
| subdivision_ranks = Species
| subdivision = {{nested taxon list
| ''Cloudina ''| Germs, 1972 |{{species list
  | Cl. hartmannae|Germs 1972
  | Cl. riemkeae  |Germs 1972
  | Cl. lucianoi  |Beurlen & Sommer, 1957) Zaine & Fairchild, 1985
  | Cl. sinensis  |Zhang, Li et Dung, 1992
  | Cl. carinata  |Cortijo, Musa, Jensena et Palacios, 2009
  | Cl. ningqiangensis  |Cai ''et al.'', 2017
  | Cl. xuanjiangpingensis  |Cai ''et al.'', 2017
  }}
| ''Conotubus'' | Zhang and Lin 1986 |{{species list
  | Co. hemiannulatus |Zhang and Lin 1986
  | (others?)
  }}
|''Acuticocloudina'' |Hahn and Pflug, 1985
}}
| synonyms = * ''Aulophycus lucianoi'' <small>Beurlen & Sommer 1957</small> = ''C. waldei'' <small>Hahn & Pflug, 1985</small> = '''''C. lucianoi''''' <small>Zaine & Fairchild, 1985</small>
}}

The '''cloudinids''', an early [[metazoan]] [[Family (biology)|family]] containing the [[genus|genera]] '''''Acuticocloudina''''', '''''Cloudina''''' and '''''Conotubus''''', lived in the late [[Ediacaran]] [[Period (geology)|period]] about 550 million years ago<ref name="NYT-20200110">{{cite news|url=https://www.nytimes.com/2020/01/10/science/fossil-guts-intestines.html|title=Fossil Reveals Earth's Oldest Known Animal Guts - The find in a Nevada desert revealed an intestine inside a creature that looks like a worm made of a stack of ice cream cones.|last=Joel|first=Lucas|date=10 January 2020|work=[[The New York Times]]|access-date=10 January 2020}}</ref><ref name="NAT-20200110" /> and became extinct at the base of the [[Cambrian]].<ref name="Yang2016">{{cite journal|doi=10.1016/j.precamres.2016.09.016|title=Transitional Ediacaran–Cambrian small skeletal fossil assemblages from South China and Kazakhstan: Implications for chronostratigraphy and metazoan evolution|journal=Precambrian Research|volume=285|pages=202–215|year=2016|last1=Yang|first1=Ben|last2=Steiner|first2=Michael|last3=Zhu|first3=Maoyan|last4=Li|first4=Guoxiang|last5=Liu|first5=Jianni|last6=Liu|first6=Pengju|bibcode=2016PreR..285..202Y}}</ref> They formed millimetre-scale conical [[fossil]]s consisting of [[calcareous]] cones nested within one another; the appearance of the organism itself remains unknown. The name ''Cloudina'' honors the 20th-century geologist and paleontologist [[Preston Cloud]].<ref name=Description />

Cloudinids comprise two genera: ''Cloudina'' itself is mineralized, whereas ''Conotubus'' is at best weakly mineralized, whilst sharing the same "funnel-in-funnel" construction.<ref>{{cite journal|doi=10.1130/G38157.1|title=The end of the Ediacaran: Two new exceptionally preserved body fossil assemblages from Mount Dunfee, Nevada, USA|journal=Geology|volume=44|issue=11|pages=911|year=2016|last1=Smith|first1=E.F.|last2=Nelson|first2=L.L.|last3=Strange|first3=M.A.|last4=Eyster|first4=A.E.|last5=Rowland|first5=S.M.|last6=Schrag|first6=D.P.|last7=MacDonald|first7=F.A.|bibcode=2016Geo....44..911S}}</ref>

Cloudinids had a wide geographic range, reflected in the present distribution of localities in which their fossils are found, and are an abundant component of some deposits. They never appear in the same layers as soft-bodied [[Ediacaran biota]], but the fact that some sequences contain cloudinids and Ediacaran biota in alternating layers suggests that these groups had different environmental preferences. It has been suggested that cloudinids lived embedded in [[microbial mat]]s, growing new cones to avoid being buried by silt. However no specimens have been found embedded in mats, and their mode of life is still an unresolved question.

The [[Taxonomy (biology)|classification]] of the cloudinids has proved difficult: they were initially regarded as [[polychaete]] worms, and then as coral-like [[cnidarian]]s on the basis of what look like [[Budding|buds]] on some specimens. Current scientific opinion is divided between classifying them as polychaetes and regarding it as unsafe to classify them as members of any broader grouping. In 2020, a new study of pyritized specimens from the [[Wood Canyon Formation]] in Nevada showed the presence of [[Nephrozoa]]n type [[Gastrointestinal tract|guts]], the oldest on record, supporting the [[bilateria]]n interpretation.<ref name="NAT-20200110">{{cite journal |author=Schiffbauer, James D. |display-authors=et al. |title=Discovery of bilaterian-type through-guts in cloudinomorphs from the terminal Ediacaran Period |date=10 January 2020 |journal=[[Nature Communications]] |volume=11 |number=205 |pages=205 |doi=10.1038/s41467-019-13882-z |pmid=31924764 |pmc=6954273 |bibcode=2020NatCo..11..205S }}</ref>

Cloudinids are important in the history of animal evolution for two reasons. They are among the earliest and most abundant of the [[small shelly fossils]] with [[Mineralization (biology)|mineralized]] [[skeleton]]s, and therefore feature in the debate about why such skeletons first appeared in the Late Ediacaran. The most widely supported answer is that their shells are a defense against predators, as some ''Cloudina'' specimens from China bear the marks of multiple attacks, which suggests they survived at least a few of them. The holes made by predators are approximately proportional to the size of the ''Cloudina'' specimens, and ''[[Sinotubulites]]'' fossils, which are often found in the same beds, have so far shown no such holes. These two points suggest that predators attacked in a selective manner, and the [[evolutionary arms race]] which this indicates is commonly cited as a cause of the [[Cambrian explosion]] of animal [[Biodiversity|diversity]] and complexity.

==Morphology==
[[File:Cloudina internal 01.png|thumb|left | 100px | Cutaway diagram of ''Cloudina'' showing "living space" within the shell.]]
''Cloudina'' varies in size from a diameter of 0.3 to 6.5&nbsp;mm, and 8 to 150&nbsp;mm in length.<ref name=Description>{{cite journal
| doi=10.2475/ajs.272.8.752
| author=Germs, G.J.B. | title=New shelly fossils from Nama Group, South West Africa
| journal=American Journal of Science |date=October 1972 | volume=272 | pages=752–761
| issue=8
| bibcode=1972AmJS..272..752G}}</ref>  Fossils consist of a series of stacked vase-like [[calcite]] tubes, whose original mineral composition is unknown,<ref name="Porter2007">{{cite journal
| journal=Science | date= 1 June 2007 |volume= 316 |issue=5829 |doi= 10.1126/science.1137284
| title= Seawater Chemistry and Early Carbonate Biomineralization |author=Porter, S.M.
| pages = 1302 | pmid= 17540895 | bibcode=2007Sci...316.1302P
| s2cid= 27418253 }}</ref> but inferred to be high-magnesium calcite.<ref>1. Zhuravlev, A.Y., Wood, R.A., and Penny, A.M. (2015). Ediacaran skeletal metazoan interpreted as a lophophorate. Proc. R. Soc. B 282, 20151860. Available at: http://rspb.royalsocietypublishing.org/lookup/doi/10.1098/rspb.2015.1860.</ref> Each cone traps a significant pore space beneath it, and stacks eccentrically in the one below. This results in a ridged external appearance.  The overall tube is curved or sinuous, and occasionally branches. The tube walls are 8 to 50 micrometers thick, usually lying in the range 10 to 25 μm.<ref name="Grant1990" /> Although it used to be thought that the tubes had test-tube like bases,<ref name="Description" /> detailed three-dimensional reconstruction has shown that the tubes had an open base.<ref name="Miller" /> There is evidence that the tube was flexible.<ref name="Brain2001" />

==Classification==
''Cloudina'' was originally classified in 1972 as a member of the Cribricyathea, a class known from the Early Cambrian.<ref name="Description" /> Glaessner (1976) accepted this classification and also
proposed that ''Cloudina'' was similar to the [[annelid]] worms, particularly [[serpulid]] [[polychaete]]s.<ref>{{cite journal
| author=Glaessner, M. F. | year=1976
| title=Early Phanerozoic annelid worms and their geological and biological significance
| journal=Journal of the Geological Society | volume=132 | pages=259–275
| doi=10.1144/gsjgs.132.3.0259
| issue=3
| bibcode=1976JGSoc.132..259G| s2cid=130795227
}}</ref> However, Hahn & Pflug (1985) and Conway Morris ''et al.''. (1990) doubted both Germs' and Glaessner's suggested relationships, and were unwilling to classify it to anything more than its own [[Family (biology)|family]], Cloudinidae.<ref>{{cite journal
|author1=Hahn, G. |author2=H. D. Pflug | year=1985
| title=Die Cloudinidae n. fam., Kalk-Röhren aus dem Vendium und Unter-Kambrium
| journal=Senckenbergiana Lethaea | volume=65 | pages=413–431
}}</ref><ref name=Conway1990 /> Some specimens of ''Cloudina hartmannae'' display budding,<ref name=Description /> which implies asexual reproduction.<ref name=Hua2005>{{cite journal
 | author = Hua, H. |author2=Chen, Z.|author3=Yuan, X.|author4=Zhang, L.|author5=Xiao, S. | year = 2005
 | title = Skeletogenesis and asexual reproduction in the earliest biomineralizing animal Cloudina
 | journal = Geology | volume = 33 | issue = 4 | pages = 277–280 | doi = 10.1130/G21198.1
 |bibcode = 2005Geo....33..277H }}</ref> On this basis Grant (1990) classified  ''Cloudina'' as a coral-like [[cnidarian]].<ref name="Grant1990" /> Since the tubes had an open base, creating a single living space rather than a series of separate chambers, ''Cloudina'' is more likely to be a [[stem group]] polychaete worm,<ref name=Miller /> in other words an evolutionary "aunt" or "cousin" of more recent polychaetes. This interpretation is reinforced by the even distribution of bore-holes made by predators.<ref name=HUA2003 /><ref name=Bengtson1992 />  However, as with so many [[Ediacaran]] life forms, there is great debate surrounding its position in the tree of life, and classification between the [[kingdom (biology)|kingdom]] and family level may be unwise.<ref name=Grant1990>{{cite journal | author = Grant, S.W. | year = 1990 | title = Shell structure and distribution of Cloudina, a potential index fossil for the terminal Proterozoic | journal = American Journal of Science | issue = 290–A | pages = 261–294 | url = http://lib.bioinfo.pl/pmid:11538690 | access-date = 2008-07-19 | pmid = 11538690 | volume = 290-A | archive-url = https://web.archive.org/web/20110522041703/http://lib.bioinfo.pl/pmid:11538690 | archive-date = 2011-05-22 | url-status = dead }}</ref><ref name=Conway1990 /><ref name=VinnZaton2012>{{cite journal
 | author = Vinn, O.
 | author2 = Zatoń, M.
 | year = 2012
 | title = Inconsistencies in proposed annelid affinities of early biomineralized organism Cloudina (Ediacaran): structural and ontogenetic evidences
 | journal = Carnets de Géologie
 | volume = CG2012_A03
 | pages = 39–47
 | doi = 10.4267/2042/46095
 | doi-access = 
 }}</ref>
<!--   ******* No ref for this, can't find one The two species of ''Cloudina'' are only distinguished on the basis of diameter, and it is possible that they in fact represent male and female forms of the same species.********  -->

==Ecology==
[[File:Cloudina NT.jpg|thumb| Restoration of ''Cloudina hartmannae'' with speculative mouth parts]]
''Cloudina'' is frequently found in association with [[stromatolites]], which are limited to shallow water; their [[isotope analysis|isotopic composition]]<ref>Ca/Mg ratios</ref> suggests that water temperatures were relatively cool. They have also been found in normal sea-floor sediments, suggesting that they were not only restricted to dwelling on microbial mounds.<ref name=domke2009>{{Walcott 2009|domke}}</ref> On the other hand, ''Cloudina'' has never been found in the same layers as the soft-bodied [[Ediacara biota]], but ''Cloudina'' and Ediacara biota have been found in alternating layers. This suggests that the two groups of organisms had different environmental preferences.<ref name="Miller" />

In many ''Cloudina'' specimens the ridges formed by the cones are of varying width, which suggests the organisms grew at a variable rate. [[Adolf Seilacher]] suggests that they adhered to [[microbial mat]]s, and that the growth phases represented the organism keeping pace with sedimentation—growing through new material deposited on it that would otherwise bury it. Kinks in the developing tube are easily explained by the mat falling slightly from the horizontal.<ref name=Seilacher1999>{{cite journal
 | author = Seilacher, A. | year = 1999 | title = Biomat-related lifestyles in the Precambrian
 | journal = PALAIOS | volume = 14 | issue = 1 | pages = 86–93
  | doi = 10.2307/3515363
 | jstor = 3515363
| bibcode = 1999Palai..14...86S }}</ref> Because of its small size, ''Cloudina'' would be expected to be found ''in situ'' in the microbial mat, especially if, as Seilacher suggests, sedimentation built up around it during its lifetime.  But all the many specimens discovered to date have only been found having been washed out of their places of growth. A further argument against Seilacher's hypothesis is that the predatory borings found in many specimens are not concentrated at what would be the top end, as one would expect if the animal was mainly buried. An alternative is that the organism dwelt on seaweeds,<ref name=Miller>{{Cite web
 | author = Miller, A.J.
 | year = 2004
 | title = A Revised Morphology of Cloudina with Ecological and Phylogenetic Implications
 | url = http://ajm.pioneeringprojects.org/files/CloudinaPaper_Final.pdf
 | access-date = 2007-04-24
 }}</ref> but until a specimen unquestionably ''in situ'' is discovered, its mode of life remains open to debate.

The tubes often appear to form colonies, although they are sometimes found in more isolated situations. The frequent appearance of large and sometimes single-species colonies has been attributed to the lack of significant predation.<ref name=Description /> On the other hand, in some locations up to 20% of ''Cloudina'' fossils contain [[predator]]y borings ranging from 15 to 400&nbsp;μm in diameter.<ref name="HUA2003">{{Cite journal|author=Hua, H.|author2=Pratt, B.R.|author3=Zhang, L.U.Y.I.|year=2003|title=Borings in Cloudina Shells: Complex Predator-Prey Dynamics in the Terminal Neoproterozoic|journal=PALAIOS|volume=18|issue=4–5|pages=454|bibcode=2003Palai..18..454H|doi=10.1669/0883-1351(2003)018<0454:BICSCP>2.0.CO;2|s2cid=131590949 |issn=0883-1351}}<!--| access-date = 2007-04-24--></ref><ref name=Bengtson1992 /> The boreholes are rather evenly distributed along the tube length, and some tubes had been bored multiple times—hence the organism could survive attacks, since predators do not attack empty shells. This may indicate that the animal could vary its position in the tube in response to predation, or that it occupied the full length—but not the full width—of the tube. The even distribution is perhaps difficult to reconcile with an [[infauna]]l lifestyle, mainly buried in a microbial mat, and adds weight to Miller's suggestion that the animal lived on seaweeds or in a reef environment. If modern-day molluscs are a suitable analogy, the size distribution of the borings suggests that the predator was similar in size to ''Cloudina''.<ref name="Brain2001">{{cite journal|author=Brain, CK|year=2001|title=Some observations on Cloudina, a terminal Proterozoic index fossil from Namibia|journal=Journal of African Earth Sciences|volume=33|issue=3|pages=475–480|bibcode=2001JAfES..33..475B|doi=10.1016/S0899-5362(01)00083-5}}<!--| access-date = 2007-04-24--></ref>

Fossil findings in the [[Nama Group]], [[Namibia]], suggest that ''Cloudina'' was one of the first reef-building animals,<ref name="natnews2014">{{Cite journal | doi = 10.1038/nature.2014.15470| title = Earliest skeletal animals were reef builders| journal = Nature| year = 2014| last1 = Morrison | first1 = J. | s2cid = 130499063}}</ref><ref name="penny2014">{{cite journal | doi = 10.1126/science.1253393 | pmid=24970084 | title=Ediacaran metazoan reefs from the Nama Group, Namibia | journal=Science | date=2014 | volume=344 | issue=6191 | pages=1504–1506 | first=A. M. | last=Penny|bibcode = 2014Sci...344.1504P | url=https://www.pure.ed.ac.uk/ws/files/16689099/Ediacaran_metazoan_reefs_Revised_1_.pdf |archive-url=https://ghostarchive.org/archive/20221010/https://www.pure.ed.ac.uk/ws/files/16689099/Ediacaran_metazoan_reefs_Revised_1_.pdf |archive-date=2022-10-10 |url-status=live | hdl=20.500.11820/44c8eba4-ec59-46d8-b868-b98c8ef1a113 | s2cid=206556938 | hdl-access=free }}</ref> but machine-learning facilitated 3D tomography indicates that the 'reef-forming' fossils are in fact simply aggregations of solitary individuals.<ref>{{Cite journal | title=Multiscale approach reveals that Cloudina aggregates are detritus and not in situ reef constructions| journal=Proceedings of the National Academy of Sciences| volume=115| issue=11| pages=E2519–E2527| date=2018-02-22| doi=10.1073/pnas.1719911115| pmid=29483244| pmc=5856547| last1=Mehra| first1=Akshay| last2=Maloof| first2=Adam| bibcode=2018PNAS..115E2519M| doi-access=free}}</ref>

==Fossil locations==
''Cloudina'' occurred in [[calcium carbonate]] rich areas of [[stromatolite]] reefs. It is found in association with ''[[Namacalathus]]'', which like ''Cloudina'' was "weakly skeletal" and solitary, and ''[[Namapoikia]]'', which was "robustly skeletal" and formed sheets on open surfaces.<ref>[http://gsa.confex.com/gsa/2005AM/finalprogram/abstract_90560.htm Neoproterozoic Microbial-Metazoan Reefs, Nama Region, Namibia] {{Webarchive|url=https://web.archive.org/web/20160307034553/http://gsa.confex.com/gsa/2005AM/finalprogram/abstract_90560.htm |date=2016-03-07 }} - abstract retrieved January 13, 2007</ref>

First found in the [[Nama Group]] in [[Namibia]],<ref name=Description /> ''Cloudina'' has also been reported in [[Oman]],<ref name=Conway1990>{{cite journal| author = Conway Morris, S.|author2=Mattes, B.W.|author3=Chen, M.| year = 1990| title = The early skeletal organism Cloudina: new occurrences from Oman and possibly China| journal = American Journal of Science| volume = 290| pages = 245–260}}</ref> [[China]]'s [[Dengying Formation]],<ref name=Conway1990 /><ref name=Bengtson1992>{{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> [[Canada]],<ref name=Hofmann2001>{{cite journal
 | author = Hofmann, H.J.
 |author2=Mountjoy, E.W.
 | date = 2001-12-01
 | title = Namacalathus-Cloudina assemblage in Neoproterozoic Miette Group (Byng Formation), British Columbia: Canada's oldest shelly fossils
 | journal = Geology
 | volume = 29
 | issue = 12
 | pages = 1091–1094
 | doi = 10.1130/0091-7613(2001)029<1091:NCAINM>2.0.CO;2
 | issn = 0091-7613
 |bibcode = 2001Geo....29.1091H 
 }}</ref> [[Uruguay]],<ref name=Gaucher1998>{{cite journal
 | author = Gaucher, C.
 |author2=Sprechmann, P.
 | year = 1998
 | title = Grupo Arroyo del Soldado: paleontologia, edad y correlaciones (Vendiano-Cámbrico Inferior, Uruguay)
 | journal = Actas II Congreso Uruguaya de Geologia, Montevideo, Sociedad Uruguaya de Geologia — Facultad de Ciencias
 | pages = 183–187
 | language=es
 }}</ref><ref name=Gaucher2000>{{cite book
 | author = Gaucher, C.
 | year = 2000
 | title = Sedimentology, palaeontology, and stratigraphy of the Arroyo del Soldado Group (Vendian to Cambrian, Uruguay)
 }}</ref> [[Argentina]],<ref>by Yochelson and Herrera, 1974; they could have mistaken them for ''Salterella''. See Grant 1990 for reference and discussion.</ref> [[Antarctica]],<ref name="Yochelson1977">{{cite journal|author=Yochelson, E.L.|author2=Stump, E.|year=1977|title=Discovery of Early Cambrian Fossils at Taylor Nunatak, Antarctica|journal=[[Journal of Paleontology]]|volume=51|issue=4|pages=872–875|issn=0022-3360|jstor=1303753}}<!--| access-date = 2007-05-18--></ref> [[Brazil]],<ref>{{Cite journal |last=Oliveira |first=Rick Souza de |last2=Nogueira |first2=Afonso César Rodrigues |last3=Romero |first3=Guilherme Raffaeli |last4=Truckenbrodt |first4=Werner |last5=da Silva Bandeira |first5=José Cavalcante |date=December 2019 |title=Ediacaran ramp depositional model of the Tamengo Formation, Brazil |url=https://linkinghub.elsevier.com/retrieve/pii/S0895981119300197 |journal=[[Journal of South American Earth Sciences]] |language=en |volume=96 |pages=102348 |doi=10.1016/j.jsames.2019.102348 |access-date=7 July 2024 |via=Elsevier Science Direct}}</ref><ref name=Zaine1985>{{cite journal
 | author = Zaine, M.F.
 |author2=Fairchild, T.R.
 | year = 1985
 | title = Comparison of Aulophycus lucianoi Beurlen & Sommer from Ladario (MS) and the genus Cloudina Germs, Ediacaran of Namibia
 | journal = Anais da Academia Brasileira de Ciências
 | volume = 57
 | pages = 130
 }}</ref> [[Nevada]],<ref name=HAGADORN2000>{{Cite journal
 | author = Hagadorn, J.W.
 |author2=Waggoner, B.
 | year = 2000
 | title = Ediacaran fossils from the southwestern Great Basin, United States
 | url = http://jpaleontol.geoscienceworld.org/cgi/content/abstract/74/2/349
 | journal = [[Journal of Paleontology]]
 | doi = 10.1666/0022-3360(2000)074<0349:EFFTSG>2.0.CO;2
 | volume = 74
 | pages = 349
 | issn = 0022-3360
 | issue = 2
 |s2cid=130774342
 }}</ref> central [[Spain]], northwest [[Mexico]] and [[California]],<ref name=Grant1990 />
in west and south [[Siberia]]. The ''Cloudina'' fossils found in association with late Precambrian-Early Cambrian [[Anabarites|anabaritids]] SSF and tubular agglutinated skeletal fossils ''[[Platysolenites]]'' and ''[[Spirosolenites]]'' in Siberia.<ref name='Kontorovich2008'>{{cite journal
 | title = A section of Vendian in the east of West Siberian Plate (based on data from the Borehole Vostok 3)
 | year = 2008
 | journal = Russian Geology and Geophysics
 | volume = 49
 | pages = 932
 | doi = 10.1016/j.rgg.2008.06.012
 | last1 = Kontorovich
 | first1 = A.
 | last2 = Varlamov
 | first2 = A.
 | last3 = Grazhdankin
 | first3 = D.
 | last4 = Karlova
 | first4 = G.
 | last5 = Klets
 | first5 = A.
 | last6 = Kontorovich
 | first6 = V.
 | last7 = Saraev
 | first7 = S.
 | last8 = Terleev
 | first8 = A.
 | last9 = Belyaev
 | first9 = S.
 | display-authors= 8
 | issue = 12
 | bibcode = 2008RuGG...49..932K
}}</ref><ref name="Zhuravlev 2009">{{cite journal|author=Andrey Yu. Zhuravlev |author2=Jose Antonio Gamez Vintaned |author3=Andrey Yu. Ivantsov |date=September 2009|title=First finds of problematic Ediacaran fossil ''Gaojiashania'' in Siberia and its origin|journal=Geological Magazine|volume=146|issue=5|pages=775–780| url=http://geolmag.geoscienceworld.org/cgi/content/abstract/146/5/775 | doi=10.1017/S0016756809990185|bibcode=2009GeoM..146..775Z|s2cid=140569611 }}</ref>
<!-- ********* duplicated
and although it is never in the same bed as "Vendozoan-type" (soft-bodied) [[Ediacaran biota|Ediacaran fossils]], it is sometimes interbedded with them, suggesting that the two classes of fossil may have occupied different habitats in close proximity.
********** --><!--
--><!-- Unreferenced **********
 This co-existence stands against [[Mark McMenamin]]'s hypothesis that the advent of skeletonisation caused the extinction of soft-bodied Ediacaran forms; however the disappearance of ''Cloudina'' at the [[Ediacaran]] - Cambrian boundary suggests that an [[extinction event]] may have occurred, which may have been related to the subsequent [[Cambrian explosion]] of life-forms. Although no Cloudinid body fossils have been found after the Ediacaran period, it has been suggested that the enigmatic trace fossils ''[[Salterella]]'' and ''[[Cornulites]]'' were formed by Cloudinids.  ********* -->

==Paleontological importance==
Although not the first [[Small shelly fossils|small shelly fossil]] to be found, ''Cloudina'' is one of the earliest and most abundant.<ref name="Bengtson2004">{{cite book |contribution=Early skeletal fossils |author=Bengtson, S. |editor1=Lipps, J.H. |editor2=Waggoner, B.M. |title=Neoproterozoic – Cambrian Biological Revolutions |year=2004 |series=Paleontological Society Papers |volume=10 |pages=67–78 |url=http://www.nrm.se/download/18.4e32c81078a8d9249800021554/Bengtson2004ESF.pdf |archive-url=https://ghostarchive.org/archive/20221010/http://www.nrm.se/download/18.4e32c81078a8d9249800021554/Bengtson2004ESF.pdf |archive-date=2022-10-10 |url-status=live |access-date=2008-07-18 |df=dmy-all |doi=10.1017/S1089332600002345}}</ref> The evolution of external shells in the Late [[Ediacaran]] is thought to be a defence against predators, marking the start of an evolutionary arms race.<ref name="Bengtson2004"/><ref name="Dzik2007VerdunSyndrome">{{cite journal |author=Dzik, J. |title=The Verdun Syndrome: Simultaneous origin of protective armour and infaunal shelters at the Precambrian–Cambrian Transition |journal=Geological Society, London, Special Publications |year=2007 |volume=286 |issue=1 |pages=405–414 |url=http://www.paleo.pan.pl/people/Dzik/Publications/Verdun.pdf |archive-url=https://ghostarchive.org/archive/20221010/http://www.paleo.pan.pl/people/Dzik/Publications/Verdun.pdf |archive-date=2022-10-10 |url-status=live |access-date=2008-07-30 |df=dmy-all |doi=10.1144/SP286.30 |bibcode=2007GSLSP.286..405D |citeseerx=10.1.1.693.9187|s2cid=33112819 }}</ref> While predatory borings are common in ''Cloudina'' specimens, no such borings have been found in ''[[Sinotubulites]]'', a similar shelly fossil sometimes found in the same beds. In addition, the diameters of borings in ''Cloudina'' are proportional to the sizes of specimens, which suggests that predators were selective about the size of their prey. These two indications that predators attacked selectively suggest the possibility of [[speciation]] in response to predation, which is often postulated as a potential cause of the [[Cambrian explosion|rapid diversification of animals in the Early Cambrian]].<ref name=Bengtson1992/>
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Can't find ref for idea that interleaving casts doubt on McMenamin that the advent of skeletonization caused the extinction of soft-bodied Ediacaran forms
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The fact that beds containing ''Cloudina'' and other shelly fossils interleave with beds containing soft-bodied [[Ediacara biota]] casts doubt on [[Mark McMenamin | McMenamin]]'s hypothesis that the advent of skeletonization caused the extinction of soft-bodied Ediacaran forms.<ref name="McMenamin1986">{{cite book |author=McMenamin M. |year=1986 |title=The Garden of Ediacara |isbn=978-0-231-10559-0 |access-date=2007-03-08 |df=dmy-all |publisher=Columbia Univ. Press |location=New York, NY}}</ref> However there is evidence of an end-Ediacaran [[mass extinction|extinction event]], which may account for the disappearance of both ''Cloudina'' and most of the Ediacara biota, and which may have been related to the subsequent [[Cambrian explosion]] of life-forms.<ref>{{cite journal |title=Decoding the Ediacaran Enigma |author1=Brasier, M. |author2=Antcliffe, J. |journal=Science |date=20 August 2004 |volume=305 |issue=5687 |doi=10.1126/science.1102673 |url=http://www.sciencemag.org/cgi/content/summary/305/5687/1115?ck=nck |access-date=2008-07-18 |df=dmy-all |pages=1115–7 |pmid=15326344}}</ref>
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==See also==
* ''[[Anabarites]]''
* ''[[Corumbella]]''
* ''[[Saarina]]''
* ''[[Sinotubulites]]''
* ''[[Somatohelix]]''
* [[List of Ediacaran genera]]


==References==
{{Reflist|25em}}

==External links==
{{commonscat|Cloudina}}

{{Taxonbar|from=Q509074}}
{{good article}}

[[Category:Prehistoric marine animals]]
[[Category:Ediacaran life]]
[[Category:Taxa described in 1985]]
[[Category:Prehistoric animal families]]