TheMaotianshan Shales (帽天山页岩) are a series ofEarly Cambriansedimentary deposits in the Chiungchussu Formation,[2] famous for theirKonservat Lagerstätten, deposits known for the exceptional preservation of fossilized organisms ortraces. The Maotianshan Shales form one of some forty Cambrian fossil locations worldwide exhibiting exquisite preservation of rarely preserved, non-mineralized soft tissue, comparable to the fossils of theBurgess Shale of British Columbia, Canada. They take their name from Maotianshan Hill (Chinese:帽天山;pinyin:Màotiānshān;lit. 'Hat Sky Mountain') inChengjiang County,Yunnan Province,China.
The most famous assemblage of organisms are referred to as theChengjiang biota for the multiple scatteredfossil sites in Chengjiang. The age of the Chengjiang Lagerstätte is locally termedQiongzhusian, a stage correlated to the lateAtdabanian Stage inSiberian sequences of the middle of theEarly Cambrian.[3][4]The shales date to ≤518 million years ago.[1]
Along with the Burgess Shale, the Maotianshan Shales are remarked as "our best window into theCambrian 'explosion'",[5] especially on the origin ofchordates.[6]
Although fossils from the region have been known from the early part of the 10th century, Chengjiang was first recognized for its exquisite states of preservation with the 1984 discovery of thenaraoiidMisszhouia, a soft-bodied relative oftrilobites. Since then, the locality has been intensively studied by scientists throughout the world, yielding a constant flow of new discoveries and triggering an extensive scientific debate surrounding the interpretation of discoveries. Over this time, taxa have been revised or reassigned to different groups. Interpretations have led to many refinements of thephylogeny of groups[7][8] and even the erection of the new phylumVetulicolia of primitivedeuterostomes.[9][10]
The Chengjiang biota has all the animal groups found in the Burgess Shale; however, since it is ten million years older, it more strongly supports the deduction that metazoans diversified earlier or faster in the early Cambrian than does the Burgess Shale fauna alone. The preservation of an extremely diverse faunal assemblage renders the Maotianshan shale the world's most important for understanding the evolution of early multi-cellular life, particularly the members of phylumChordata, which includes allvertebrates. The Chengjiang fossils comprise the oldest diversemetazoan assemblage above theProterozoic-Phanerozoic transition and, thus, thefossil record's best data source for understanding the apparently rapid diversification of life known as theCambrian Explosion.
One of the most intriguing locations of the Chengjiang biota is the Haiyan Lagerstätte where hundreds of juvenile specimens have been found. This unique location offers insights into the development of most animal groups and as such is a unique deposit in the Cambrian.[11]
In respect of 'the Chengjiang fossils represent[ing] an uparalleled record of the fundamentally important rapid diversification of metazoan life in the early Cambrian', theInternational Union of Geological Sciences (IUGS) included the 'Cambrian Chengjiang fossil site and lagerstätte' in its assemblage of 100 'geological heritage sites' around the world in a listing published in October 2022. The organisation defines an 'IUGS Geological Heritage Site' as 'a key place with geological elements and/or processes of international scientific relevance, used as a reference, and/or with a substantial contribution to the development of geological sciences through history.'[12]
The fossils occur in a section of mudstone 50 metres (160 ft) thick in theYuanshan Member of theQiongzhusi Formation. The Yuanshan Member is extensive, covering multiple 10,000 square kilometres (3,900 sq mi) of eastern Yunnan Province, where there are many scattered outcrops yielding fossils. Studies of the strata are consistent with a tropical environment with sea level changes and tectonic activity. The region is believed to have been a shallow sea with a muddy bottom. The preserved fauna is primarilybenthic and was likely buried by periodicturbidity currents, since most fossils do not show evidence of post-mortem transport. Like the younger Burgess Shale fossils, the paleo-environment enabled preservation of non-mineralized, soft body parts. Fossils are found in thin layers less than an inch thick. The soft parts are preserved as aluminosilicate films, often with high oxidized iron content and often exhibiting exquisite details.
The Chengjiang beds are very deeply weathered, as evidenced by their lowspecific gravity (i.e., they are very lightweight).[13] Trace fossils are abundant.[14]
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. PhylumPorifera (sponges; 15 species) andPriapulida (16 species) are also well represented. Other phyla represented areBrachiopoda,Chaetognatha,Cnidaria,Ctenophora,Echinodermata,Hyolitha,Nematomorpha,Phoronida, andChordata. Possiblemolluscs includeWiwaxia.[15]
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 asbenthic environments rapidly changed in the Cambrian. Chengjiang is the richest source of theLobopodia, a group including many earlypanarthropods,[16] with six genera represented:Luolishania,Paucipodia,Cardiodictyon,Hallucigenia (also known from the Burgess Shale),Microdictyon, andOnychodictyon.
Perhaps the most important fossils from Chengjiang are eight possible members of phylumChordata, the phylum to which all vertebrates belong. The most famous isMyllokunmingia, possibly a very primitive agnathid (i.e.,jawless fish). Similar toMyllokunmingia isHaikouichthys ercaicunensis, another primitive fish-like animal.
A wide range of affinities have been proposed for the enigmaticYunnanozoon lividum including stemcephalochordates, stem or crownhemichordates,craniates, stemdeuterostomes, stembilaterians, orambulacrarians.[17] Specimens initially identified asHaikouella (a genus later deemed a junior synonym ofYunnanozoon)[18] display has several chordate features, including a discernible heart, dorsal and ventral aorta, gill filaments, and anotochord (neural chord).[19] A 2024 study placedYunnanozoon along the chordate stem.[20]
Another much-debated group is theVetulicolia, starting with the discovery ofVetulicola in 1987. Close Chengjiang relatives ofVetulicola includeBeidazoon and theDidazoonids.Heteromorphus is more closely related toBanffia from theBurgess Shale, but both it andBanffia are also considered to be vetulicolians.[21] Originally described as crustacean arthropods, theVetulicola were later erected as a new phylum of primitive deuterostomes by D.G. Shu.[5] In recent years, a majority of workers have come to see the vetulicolians as stem chordates,[22] and a 2024 study placed vetulicolians as a basal chordateevolutionary grade, followed byYunnanozoon.[20] An alternative proposal places vetulicolians as a sister group to tunicates.[23] Vetulicolians are thought to have been swimmers that either were filter feeders or detritivores.[24]
Some two dozen animals from the Chengjiang biota are problematic regarding phylogenetic assignment. Among these,'Anomalocaris' saron, the alleged predatory terror of the early Cambrian, was the most famous, although that species is later reclassified toHoucaris saron andInnovatiocaris maotianshanensis. Shu (2006) recently describedStromatoveris psygmoglena as a possiblebilateran missing link betweenEdiacaran fronds and Cambrianctenophores.Cambrocornulitus had a tubicolous shell which probably was biomineralized. It shares some affinities with cornulitids and lophophorates.[25]
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.[26]
Located in the Yunnan Province of South China and hosted in the geologically distinctCambrian Stage 4Wulongqing Formation, The Guanshan biota are also Burgess shale-type fossils but slightly younger than the Chengjian biota with an age dating to 515–510Myr.[27][28] Brachiopods are the most abundant species,[29] followed by trilobites. Other species belong to sponges, chancelloriids, cnidarians, ctenophores, priapulids, lobopodians, arthropods, anomalocaridids, hyoliths, molluscs, brachiopods, echinoderms, algae and vetulicolians. There are also the earliest-known eocrinoids, unidentified soft-bodied animals and abundant trace fossils.[30]
^Yang, X.; Kimmig, J.; Zhai, D.; Liu, Y.; Kimmig, S. R.; Peng, S. (2021). "A juvenile-rich palaeocommunity of the lower Cambrian Chengjiang biota sheds light on palaeo-boom or palaeo-bust environments".Nature Ecology & Evolution.5 (8):1082–1090.Bibcode:2021NatEE...5.1082Y.doi:10.1038/s41559-021-01490-4.PMID34183806.S2CID235674619.
^Gaines, R. R.; Briggs, D. E. G.; Yuanlong, Z. (2008). "Cambrian Burgess Shale–type deposits share a common mode of fossilization".Geology.36 (10):755–758.Bibcode:2008Geo....36..755G.doi:10.1130/G24961A.1.
^Hou, Xian-guang; Siveter, David J.; Siveter, Derek J.; Aldridge, Richard J.; Cong, Pei-yun; Gabbott, Sarah; Ma, Xiao-ya; Purnell, Mark A.; Williams, Mark (2017). "Bilateria of Uncertain Affinity".The Cambrian Fossils of Chengjiang, China: The Flowering of Early Animal Life (2 ed.). pp. 264–271.doi:10.1002/9781118896372.ch25.
^Hou, Xian-guang; Siveter, David J.; Siveter, Derek J.; Aldridge, Richard J.; Cong, Pei-yun; Gabbott, Sarah; Ma, Xiao-ya; Purnell, Mark A.; Williams, Mark (2017). "Vetulicolians".The Cambrian Fossils of Chengjiang, China: The Flowering of Early Animal Life (2 ed.). pp. 272–281.doi:10.1002/9781118896372.ch25.
^Aldridge, Richard J.; Hou, Xian-guang; Siveter, David J.; Siveter, Derek J.; Sarah E., Gabbott (2007). "The systematics and phylogenetic relationships of vetulicolians".Palaeontology.50:131–168.doi:10.1111/j.1475-4983.2006.00606.x.S2CID85722738.
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Shu, D. G.; Conway Morris, S.; Han, J.; Chen, L.; Zhang, X. L.; Zhang, Z. F.; et al. (2001). "Primitive deuterostomes from the Chengjiang Lagerstatte (Lower Cambrian, China)".Nature.414 (6862):419–424.Bibcode:2001Natur.414..419S.doi:10.1038/35106514.PMID11719797.S2CID4345484.
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