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The Maotianshan shale is a lower Cambrian Konservat Lagerstätte named for Maotianshan Hill in Chengjiang County, Yunnan Province, China. More commonly, the multiple, scattered fossil sites are referred to as the Chengjiang biota after its extremely diverse assemblage of organisms, and more simply still, just Chengjiang. The Chengjiang fauna occurs in outcrops of the Qiongzhusi Formation that date to between 525 and 520 mya, or to about the middle of the early Cambrian epoch, at least some 10 million years earlier than the Burgess Shale. It is one of some 40 Cambrian, fossil locations worldwide exhibiting Burgess Shale-like, exquisite preservation of rarely preserved, non-mineralized soft-tissue. 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 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 an extensive literature, a constant flow of new discoveries, as well as 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 has all the animal groups found in the Burgess Shale. However, since it is 10 million years younger, it supports the deduction of earlier or faster diversification of metazoans in the early Cambrian than does the Burgess Shale fauna. The preservation of an extremely diverse faunal assemblage renders the Maotianshan shale as the world’s most important locality for understanding the evolution of early multi-cellular life, and particularly the members of phylum Chordata that 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 50 meter thick section of mudstone 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 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 and oxidized iron content, 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 hard, mineral-reinforced exoskeletons. 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 species of Chengjiang trilobites have been found with traces of legs, antennae, and other soft body parts, an exceedingly rare occurrence in the fossil record. Phylum Porifera (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 species represented: Luolishania, Paucipodia, Cardiodictyon, Hallucigenia (also known from the Burgess Shale), Microdictyon, and Onychodictyon. Perhaps the most important fossils from Chengjiang are eight putative 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). The enigmatic Yannanozoon 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 the Yunnanozoon lividum, but also differs in several aspects: it has a discernible heart, dorsal and ventral aorta, gill filaments, and a notochord (neural chord). Similar to Myllokunmingia, Haikouichthys ercaicunensis is another fish-like primitive, fish-like animal. Originally described as crustacean arthropods, Shu (2001) later erected the Vetulicola as a new phylum of primitive deuterostomes that is represented by seven species from Chengjiang. Another researcher places them with the Urochordates based on putative affinity with the Phylum Chordata. At present, there is no agreement as to their systematic placement. 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[http://www.fossilmuseum.net/Fossil_Sites/Chengjiang/Chengjiang-Biota.htm] Phylum Arthropoda - 77 species Phylum Arthropoda - Arachnomorpha - 2 species Phylum Arthropoda - Class Trilobita - 5 species Phylum Brachiopoda - 5 species Phylum Chaetognatha - 1 species Phylum Cnidaria - 2 species Phylum Chordata - 8 species Phylum Ctenophora - 3 species Phylum Echinodermata - 1 species Enigmatic - 24 species Phylum Hyolitha - 8 species Phylum Lobopodia - 6 species Phylum Nematomorpha - 3 species Phylum Phoronida - 1 species Phylum Porifera - 15 species Kingdom Protista (algae) - 4 species Phylum Priapulida - 16 species Phylum Uncertain - 4 species Phylum Vetulicolia - 7 species See also | |||||||
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