Maotianshan Shales

Maotianshan Shale
Stratigraphic range: Cambrian Stage 3, Qiongzhusian age local stage ≤518 Ma[1] PreꞒ Ꞓ O S D C P T J K Pg N ↓
Outcrop of the Maotianshan Shale, site of the discovery of the Chengjiang Biota
Type	Member
Unit of	Chiungchussu Formation
Area	multiple 10,000 km2 (3,900 sq mi)
Thickness	50 m (160 ft)
Lithology
Primary	Shale
Other	Mudstone
Location
Coordinates	26°42′N 108°24′E / 26.7°N 108.4°E / 26.7; 108.4
Approximate paleocoordinates	28°06′N 154°18′E / 28.1°N 154.3°E / 28.1; 154.3
Region	Chengjiang County, Yunnan
Country	China
Type section
Named for	Maotianshan Hill
Location	Maotianshan Hill
Region	Chengjiang County, Yunnan
Country	China

Part of a series on
The Cambrian explosion
Fossil localities Burgess Shale Chengjiang Sirius Passet Doushantuo
Key organisms Ediacaran biota Dickinsonia Kimberella Kimberichnus Vernanimalcula Burgess-type Marrella Radiodonts Halwaxiids Opabinia Odontogriphus Small shelly fauna Helcionellids
Evolutionary concepts Trends Cambrian substrate revolution Themes Cladistics Convergent evolution Stem and crown groups
v t e

The Maotianshan Shales (帽天山页岩) are a series of Early Cambrian sedimentary deposits in the Chiungchussu Formation,^[2] famous for their Konservat Lagerstätten, deposits known for the exceptional preservation of fossilized organisms or traces. 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 the Burgess Shale of British Columbia, Canada. They take their name from Maotianshan Hill (Chinese: 帽天山; pinyin: Màotiānshān; lit. 'Hat Sky Mountain') in Chengjiang County, Yunnan Province, China.

The most famous assemblage of organisms are referred to as the Chengjiang biota for the multiple scattered fossil sites in Chengjiang. The age of the Chengjiang Lagerstätte is locally termed Qiongzhusian, a stage correlated to the late Atdabanian Stage in Siberian sequences of the middle of the Early 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 the Cambrian 'explosion'",^[5] especially on the origin of chordates.^[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 the naraoiid Misszhouia, a soft-bodied relative of trilobites. 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 the phylogeny of groups^[7][8] and even the erection of the new phylum Vetulicolia of primitive deuterostomes.^[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 phylum Chordata, which includes all vertebrates. The Chengjiang fossils comprise the oldest diverse metazoan assemblage above the Proterozoic-Phanerozoic transition and, thus, the fossil record's best data source for understanding the apparently rapid diversification of life known as the Cambrian 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', the International 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 the Yuanshan Member of the Qiongzhusi 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 primarily benthic and was likely buried by periodic turbidity 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 low specific 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. 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 molluscs include Wiwaxia and Nectocaris.^[15][16]

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 environments rapidly changed in the Cambrian. Chengjiang is the richest source of the Lobopodia, a group including many early panarthropods,^[17] 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.

The enigmatic Yunnanozoon lividum is considered to be the earliest hemichordate, possessing many of the characteristic chordate features and providing an anatomical link between invertebrates and chordates. Haikouella lanceolata is described to be the earliest craniate-like chordate. This fish-like animal has many similarities to Y. lividum, but differs in several aspects: It has a discernible heart, dorsal and ventral aorta, gill filaments, and a notochord (neural chord).

At present, there is no agreement as to the systematic placement of the Vetulicola, represented by seven species from Chengjiang. Originally described as crustacean arthropods, the Vetulicola were later erected as a new phylum of primitive deuterostomes by D.G. Shu et al. (Shu 2001). Another researcher places them with the urochordates, based on putative affinity with the phylum Chordata. They are thought to have been swimmers that either were filter feeders or detritivores.

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 to Houcaris saron and Innovatiocaris maotianshanensis. Shu (2006) recently described Stromatoveris psygmoglena as a possible bilateran missing link between Ediacaran fronds and Cambrian ctenophores. Cambrocornulitus had a tubicolous shell which probably was biomineralized. It shares some affinities with cornulitids and lophophorates.^[18]

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.^[19]

Located in the Yunnan Province of South China and hosted in the geologically distinct Cambrian Stage 4 Wulongqing Formation, The Guanshan biota are also Burgess shale-type fossils but slightly younger than the Chengjian biota with an age dating to 515–510 Myr.^[20][21] Brachiopods are the most abundant species,^[22] 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.^[23]

The Guanshan biota are regarded as successors of the Chengjian biota,^[21] and share many species. The unique species include arthropods like Guangweicaris^[24] and Astutuscaris,^[25] vetulicolians like Vetulicola gantoucunensis^[26] and V. longbaoshanensis.;^[27] chordates like Cathaymyrus haikouensis and Zhongxiniscus intermedius.^[28]

• 
  Misszhouia longicaudata
• 
  Heliomedusa orienta
• 
  Leanchoilia illecebrosa

• Geography of China
• Stephen Jay Gould, Wonderful Life
• List of arthropods of the Cambrian Period

• Conway-Morris, S. (2003). "The Cambrian "explosion" of metazoans and molecular biology: would Darwin be satisfied?". Int J Dev Biol. 47 (7–8): 505–515. PMID 14756326.
• Fossils of the Chengjiang Maotianshan Shale - URL retrieved September 20, 2006
• Hou, Xian-Guang; Aldridge, Richard J., Bengstrom, Jan; Siveter, David J. ;Feng, Xiang-Hong 2004; The Cambrian Fossils of Chengjang, China, Blackwell Science Ltd, 233 pp.
• Preservation, Taphonomy and Palaeoecology of the Chengjiang Biota - URL retrieved September 20, 2006
• Shu, D-G; Luo, H-L; Conway Morris, S.; Zhang, X-L; Hu, S-X; Chen, L.; Han, J.; Zhu, M.; Li, Y; et al. (1999). "Lower Cambrian Vertebrates from South China". Nature. 402 (6757): 42–46. Bibcode:1999Natur.402...42S. doi:10.1038/46965. S2CID 4402854.
• 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. PMID 11719797. S2CID 4345484.
• Shu, D.; Conway Morris, S.; Zhang, Z. F.; Liu, J. N.; Han, J.; Chen, L.; et al. (2003). "A new species of yunnanozoan with implications for deuterostome evolution". Science. 299 (5611): 1380–1384. doi:10.1126/science.1079846. PMID 12610301. S2CID 45702564.
• Shu, D. G.; Conway Morris, S.; Han, J.; Zhang, Z. F.; Liu, J. N. (2004). "Ancestral echinoderms from the Chengjiang deposits of China". Nature. 430 (6998): 422–428. doi:10.1038/nature02648. PMID 15269760. S2CID 4421182.
• Shu, D. G.; Conway Morris, S.; Han, J.; Li, Y.; Zhang, X. L.; Hua, H.; et al. (2006). "Lower Cambrian vendobionts from China and early diploblast evolution". Science. 312 (5774): 731–734. Bibcode:2006Sci...312..731S. doi:10.1126/science.1124565. PMID 16675697. S2CID 1235914.
• Waloszek, D.; Maas, A. (2005). "The evolutionary history of crustacean segmentation: a fossil-based perspective". Evol Dev. 7 (6): 515–527. doi:10.1111/j.1525-142x.2005.05056.x. PMID 16336406. S2CID 27327765.
• Xian-guang, H.; Aldridge, R. J.; Siveter, D. J.; Xiang-hong, F. (2002). "New evidence on the anatomy and phylogeny of the earliest vertebrates". Proc Biol Sci. 269 (1503): 1865–1869. doi:10.1098/rspb.2002.2104. PMC 1691108. PMID 12350247.
• Zhang, X.; Han, J.; Zhang, Z.; Liu, H.; Shu, D. (2003). "Reconsideration of the supposed naraoiid larva from the Early Cambrian Chengjiang Lagerstätte, South China". Palaeontology. 46 (3): 447–66. Bibcode:2003Palgy..46..447Z. doi:10.1111/1475-4983.00307.
• Zhang, X. G.; Hou, X. G. (2004). "Evidence for a single median fin-fold and tail in the Lower Cambrian vertebrate, Haikouichthys ercaicunensis". J Evol Biol. 17 (5): 1162–1166. doi:10.1111/j.1420-9101.2004.00741.x. PMID 15312089.

• "Chengjiang". Archived from the original on 2005-10-24. Retrieved 2005-11-22.
• Chengjiang Biota at fossilmuseum.net