Everything about Maotianshan Shale totally explained
In the
Maotianshan shales is a lower
Cambrian Konservat Lagerstätte named for Maotianshan Hill (|s=|p=Màotiānshān}}) in
Chengjiang County,
Yunnan Province,
China. More commonly, the extremely diverse assemblage of organisms are referred to as the
Chengjiang biota for the multiple scattered
fossil sites in Chengjiang. The Chengjiang fauna occur in outcrops of the Qiongzhusi Formation that date to between 525 and - a period situated in the middle of the early
Cambrian epoch and at least some 10 million years older than the
Burgess Shale. The Maotianshan shale is 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.
History and scientific significance
Although fossils from the region have been known from the early part of the twentieth 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 from throughout the world, yielding a constant flow of new discoveries and an extensive literature expressing scientific debate surrounding the interpretation of discoveries. Over this time, various taxa have been revised or re-assigned to different groups. Interpretations have led to many refinements of the
phylogeny of various groups and even the erection of the new phylum
Vetulicolia of primitive
deuterostomes. The Chengjiang biota already has all the animal groups found in the Burgess Shale; however, since it's 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 locality for understanding the evolution of early multi-cellular life, and 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.
Preservation and Taphonomy
Fossils occur in a section of mudstone fifty meters thick in the Yuanshan Member of the Qiongzhusi Formation. The Yuanshan Member is extensive, covering tens of thousands of square kilometers of eastern Yunnan Province, where there are numerous, 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 don't 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.
Fauna
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, and 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,
Protista, and
Chordata. 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, often considered a distinct phylum, 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 (for example,
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 also differs in several aspects: it has a discernible heart, dorsal and ventral aorta, gill filaments, and a
notochord (neural chord).
At present, there's 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, is the most famous. Shu (2006) recently described
Stromatoveris psygmoglena as a possible
bilateran missing link between
Ediacaran fronds and Cambrian
ctenophores.
List of Chengjiang Biota species by phylum
Further Information
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