Editing Maotianshan Shales (section)

== Chengjiang fauna ==
[[File:Haikouella lanceolata China.jpg|thumb|''[[Haikouella lanceolata]]'', Maotianshan Shales, Chengjiang County, Yunnan Province]]
{{further|Paleobiota of the Maotianshan Shales}}
The Chengjiang biota comprises an extremely diverse faunal assembly, with some 185 species described in the literature as of June 2006. Of these, nearly half are arthropods, few of which had the hard, mineral-reinforced exoskeletons characteristic of all later arthropoda; only about 3% of the organisms known from Chengjiang have hard shells. Most of those are the trilobites (of which there are five species), all of which have been found with traces of legs, antennae, and other soft body parts, an exceedingly rare occurrence in the fossil record. Phylum [[Porifera]] (sponges; 15 species) and [[Priapulida]] (16 species) are also well represented. Other phyla represented are [[Brachiopoda]], [[Chaetognatha]], [[Cnidaria]], [[Ctenophora]], [[Echinodermata]], [[Hyolitha]], [[Nematomorpha]], [[Phoronida]], and [[Chordata]]. Possible [[Mollusca|molluscs]] include ''[[Wiwaxia]]''.<ref>{{Cite journal | doi = 10.1017/S0016756814000648| title = First report of ''Wiwaxia'' from the Cambrian Chengjiang Lagerstätte| journal = [[Geological Magazine]]| pages = 378–382| volume = 152 | issue = 2| year = 2015| last1 = Zhao | first1 = F. C. | last2 = Smith | first2 = M. R. | last3 = Yin | first3 = Z.-J. | last4 = Zeng | first4 = H. | last5 = Hu | first5 = S.-X | last6 = Li | first6 = G.-X. | last7 = Zhu | first7 = M.-Y.| bibcode = 2015GeoM..152..378Z| s2cid = 129654292| url = https://www.repository.cam.ac.uk/bitstream/1810/246363/1/201X-ZHAO-Smith-et-al-Chengjiang-Wiwaxia.pdf }}</ref>

About one in eight animals are problematic forms of uncertain affinity, some of which may have been evolutionary experiments that survived for only a brief period as [[Benthic zone|benthic]] environments rapidly changed in the Cambrian. Chengjiang is the richest source of the [[Lobopodia]], a group including many early [[panarthropod]]s,<ref>{{Cite journal | doi = 10.1038/nature13576 | pmid = 25132546 | journal = [[Nature (journal)|Nature]] | volume = 514 | issue = 7522 | pages = 363–366 | last1 = Smith | first1 = M. R.  | title = Hallucigenia's onychophoran-like claws and the case for Tactopoda | last2 = Ortega Hernández | first2 = J. | url = http://rdcu.be/bKoD| year = 2014 | bibcode = 2014Natur.514..363S | s2cid = 205239797 }}</ref> with six genera represented:  ''[[Luolishania]]'', ''[[Paucipodia]]'', ''[[Cardiodictyon]]'','' [[Hallucigenia]]'' (also known from the Burgess Shale), ''[[Microdictyon]]'', and ''[[Onychodictyon]]''.

Perhaps the most important fossils from Chengjiang are eight possible members of phylum [[Chordata]], the phylum to which all vertebrates belong. The most famous is ''[[Myllokunmingia]]'', possibly a very primitive agnathid (i.e., [[jawless fish]]). Similar to ''Myllokunmingia'' is ''[[Haikouichthys]] ercaicunensis'', another primitive fish-like animal.

A wide range of affinities have been proposed for the enigmatic ''[[Yunnanozoon|Yunnanozoon lividum]]'' including stem [[cephalochordates]], stem or crown [[hemichordates]], [[craniates]], stem [[deuterostomes]], stem [[bilaterians]], or [[ambulacrarians]].<ref>{{cite book|last1=Hou |first1=Xian-guang |last2=Siveter |first2=David J. |last3=Siveter |first3=Derek J. |last4=Aldridge |first4=Richard J. |last5=Cong |first5=Pei-yun |last6=Gabbott |first6=Sarah |last7=Ma |first7=Xiao-ya |last8=Purnell |first8=Mark A. |last9=Williams |first9=Mark |title=The Cambrian Fossils of Chengjiang, China: The Flowering of Early Animal Life |chapter=Bilateria of Uncertain Affinity |edition=2 |date=2017 |pages=264–271 |doi=10.1002/9781118896372.ch25}}</ref>  Specimens initially identified as ''Haikouella'' (a genus later deemed a junior synonym of ''Yunnanozoon'')<ref>{{Cite journal |last1=Cong |first1=Pei-Yun |last2=Hou |first2=Xian-Guang |last3=Aldridge |first3=Richard J. |last4=Purnell |first4=Mark A. |last5=Li |first5=Yi-Zhen |date=2015 |editor-last=Smith |editor-first=Andrew |title=New data on the palaeobiology of the enigmatic yunnanozoans from the Chengjiang Biota, Lower Cambrian, China |url=https://onlinelibrary.wiley.com/doi/10.1111/pala.12117 |journal=Palaeontology |language=en |volume=58 |issue=1 |pages=45–70 |doi=10.1111/pala.12117|s2cid=84567733 }}</ref> display has several chordate features, including a discernible heart, dorsal and ventral aorta, gill filaments, and a [[notochord]] (neural chord).<ref>{{Cite journal |last=Chen |first=Jun-Yuan |last2=Huang |first2=Di-Ying |last3=Li |first3=Chia-Wei |date=December 1999 |title=An early Cambrian craniate-like chordate |url=https://www.nature.com/articles/990080 |journal=Nature |language=en |volume=402 |issue=6761 |pages=518–522 |doi=10.1038/990080 |issn=0028-0836}}</ref>  A 2024 study placed ''Yunnanozoon'' along the chordate stem.<ref name=Mussini2024>{{cite journal |last1=Mussini |first1=G. |last2=Smith |first2=M. P. |last3=Vinther |first3=J. |last4=Rahman |first4=I. A. |last5=Murdock |first5=D. J. E. |last6=Harper |first6=D. A. T. |last7=Dunn |first7=F. S. |title=A new interpretation of ''Pikaia'' reveals the origins of the chordate body plan |journal=Current Biology |date=2024 |volume=34 |issue=13 |pages=2980–2989.e2 |doi=10.1016/j.cub.2024.05.026 |doi-access=free |pmid=38866005 }}</ref>

Another much-debated group is the [[Vetulicolia]], starting with the discovery of ''[[Vetulicola]]'' in 1987.  Close Chengjiang relatives of ''Vetulicola'' include ''[[Beidazoon]]'' and the [[Didazoonids]].  ''[[Heteromorphus]]'' is more closely related to ''[[Banffia]]'' from the [[Burgess Shale]], but both it and ''Banffia'' are also considered to be vetulicolians.<ref name=Vetulicolia>{{cite book|last1=Hou |first1=Xian-guang |last2=Siveter |first2=David J. |last3=Siveter |first3=Derek J. |last4=Aldridge |first4=Richard J. |last5=Cong |first5=Pei-yun |last6=Gabbott |first6=Sarah |last7=Ma |first7=Xiao-ya |last8=Purnell |first8=Mark A. |last9=Williams |first9=Mark |title=The Cambrian Fossils of Chengjiang, China: The Flowering of Early Animal Life |chapter=Vetulicolians |edition=2 |date=2017 |pages=272–281 |doi=10.1002/9781118896372.ch25}}</ref> Originally described as crustacean arthropods, the ''Vetulicola'' were later erected as a new phylum of primitive deuterostomes by D.G. Shu.<ref name=":02" />  In recent years, a majority of workers have come to see the vetulicolians as stem chordates,<ref name=Onai2023>{{cite journal|last1=Onai |first1=Takayuki |last2=Aramaki |first2=Toshihiro |last3=Takai |first3=Akira |last4=Kakiguchi |first4=Kisa |last5=Yonemura |first5=Shigenobu |title=Cranial cartilages: Players in the evolution of the cranium during evolution of the chordates in general and of the vertebrates in particular |journal=Evolution and Development |volume=25 |pages=197–208 |year=2023 |doi=10.1111/ede.12433|doi-access=free }}</ref> and a 2024 study placed vetulicolians as a basal chordate [[evolutionary grade]], followed by ''Yunnanozoon''.<ref name=Mussini2024 />  An alternative proposal places vetulicolians as a sister group to tunicates.<ref>{{cite journal|last1=García-Bellido |first1=Diego C. |last2=Lee |first2=Michael S. Y. |last3=Edgecombe |first3=Gregory D. |last4=Jago |first4=James B. |last5=Gehling |first5=James G. |last6=Paterson |first6=John R. |year=2014 |title=A new vetulicolian from Australia and its bearing on the chordate affinities of an enigmatic Cambrian group |journal=BMC Evolutionary Biology |volume=14 |page=214 |doi=10.1186/s12862-014-0214-z |pmc=4203957 |pmid=25273382 |doi-access=free }}</ref> Vetulicolians are thought to have been swimmers that either were filter feeders or detritivores.<ref>{{cite journal |last1=Aldridge |first1=Richard J. |last2=Hou |first2=Xian-guang |last3=Siveter |first3=David J. |last4=Siveter |first4=Derek J. |last5=Sarah E. |first5=Gabbott |year=2007 |title=The systematics and phylogenetic relationships of vetulicolians |journal=Palaeontology |volume=50 |pages=131–168 |doi=10.1111/j.1475-4983.2006.00606.x |s2cid=85722738}}</ref>

Some two dozen animals from the Chengjiang biota are problematic regarding phylogenetic assignment. Among these, ''<nowiki/>'[[Anomalocaris]]' saron'', the alleged predatory terror of the early Cambrian, was the most famous, although that species is later reclassified to ''[[Houcaris]] saron'' and ''[[Innovatiocaris]] maotianshanensis''. Shu (2006) recently described ''[[Stromatoveris]] psygmoglena'' as a possible [[Bilateria|bilateran]] missing link between [[Ediacaran]] fronds and Cambrian [[ctenophore]]s. ''[[Cambrocornulitus]]'' had a tubicolous shell which probably was biomineralized. It shares some affinities with cornulitids and lophophorates.<ref name='VinnWilsonMotus2013'>{{cite journal
 | doi = 10.1080/11035897.2013.801035
 | title = New tubicolous problematic fossil with some "lophophorate" affinities from the Early Cambrian Chengjiang biota in south China
 | year = 2013
 | author = Xianfeng, Y.
 | author2 = Vinn, O.
 | author3 = Xianguang, H.
 | author4 = Xinglei, T.
 | journal = GFF
 | volume = 135
 | issue = 2
 | pages = 184–190 
 | bibcode = 2013GFF...135..184Y
 | s2cid = 129033570
 | url = https://www.researchgate.net/publication/258180839
 | access-date = 2014-06-11}}</ref>

The Chengjiang biota is believed to have inhabited a delta front environment rich in oxygen, with high sedimentation rates and major fluctuations in salinity being the main environmental stressors.<ref>{{cite journal |last1=Saleh |first1=Farid |last2=Qi |first2=Changshi |last3=Buatois |first3=Luis A. |last4=Mángano |first4=M. Gabriela |last5=Paz |first5=Maximiliano |last6=Vaucher |first6=Romain |last7=Zheng |first7=Quanfeng |last8=Hou |first8=Xian-Guang |last9=Gabbott |first9=Sarah E. |last10=Ma |first10=Xiaoya |date=23 March 2022 |title=The Chengjiang Biota inhabited a deltaic environment |journal=[[Nature Communications]] |volume=13 |issue=1 |page=1569 |pmc=8943010 |pmid=35322027 |doi=10.1038/s41467-022-29246-z |bibcode=2022NatCo..13.1569S }}</ref>