Maotianshan Shales

Coordinates: 28°06′N 154°18′E / 28.1°N 154.3°E / 28.1; 154.3
Source: Wikipedia, the free encyclopedia.
Maotianshan Shale
Ma[1]
↓
Chengjiang County, Yunnan
Country China
Part of a series on
The Cambrian explosion
Fossil localities
Key organisms
Ediacaran biota
Burgess-type
Small shelly fauna
Evolutionary concepts
Trends
Themes

The Maotianshan Shales (帽天山页岩) are a series of

Chengjiang County, Yunnan Province, China
.

The most famous assemblage of organisms are referred to as the Chengjiang biota for the multiple scattered

Early Cambrian.[3][4]
The shales date to ≤518 million years ago.
Malong District in Yunnan,[3] Kaili biota and Balang fauna in Guizhou, Shipai fauna in Hubei, and sponge faunas of Guizhou and Anhui.[5]

Along with the Burgess Shale, the Maotianshan Shales are remarked as "our best window into the

chordates.[7]

History and scientific significance

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

deuterostomes.[citation needed
]

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

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.[8]

IUGS geological heritage site

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.'[9]

Preservation and taphonomy

Maotianshania cylindrica, a fossil nematomorph worm, Early Cambrian, Chengjiang Maotianshan Shales
Further information:
Burgess shale type preservation

The fossils occur in a section of mudstone 50 metres (160 ft) thick in the

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).[10] Trace fossils are abundant.[11]

Chengjiang fauna

Haikouella lanceolata
, Maotianshan Shales, Chengjiang County, Yunnan Province
Further information: List of Chengjiang Biota species by phylum

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

Chordata. Possible molluscs include Wiwaxia and Nectocaris.[12][13]

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

panarthropods,[14] 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

jawless fish). Similar to Myllokunmingia is Haikouichthys
ercaicunensis, another primitive fish-like animal.

The enigmatic

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, '

ctenophores. Cambrocornulitus had a tubicolous shell which probably was biomineralized. It shares some affinities with cornulitids and lophophorates.[15]

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.[16]

Guanshan biota

Located at the Yunnan Province of South China, the Guanshan biota are also Burgess shale-type fossils but slightly younger than the Chengjian biota, and is dated to 515–510

Myr falling within the Cambrian Stage 4.[17][18] Brachiopods are the most abundant species,[19] 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.[5]

The Guanshan biota are regarded as successors of the Chengjian biota,[18] and share many species. The unique species include arthropods like Guangweicaris[20] and Astutuscaris,[21] vetulicolians like Vetulicola gantoucunensis[22] and V. longbaoshanensis.[23]; chordates like Cathaymyrus haikouensis and Zhongxiniscus intermedius.[24]

Gallery

See also

References

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  9. ^ "The First 100 IUGS Geological Heritage Sites" (PDF). IUGS International Commission on Geoheritage. IUGS. Archived (PDF) from the original on 2022-10-27. Retrieved 13 November 2022.
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  18. ^
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  19. S2CID 59439966. Archived
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  20. S2CID 201291723. Archived
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  22. S2CID 129031316. Archived
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  24. S2CID 84505454. Archived
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Further reading

External links
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