Maotianshan shales
Encyclopedia
Cambrian
The Cambrian is the first geological period of the Paleozoic Era, lasting from Mya ; it is succeeded by the Ordovician. Its subdivisions, and indeed its base, are somewhat in flux. The period was established by Adam Sedgwick, who named it after Cambria, the Latin name for Wales, where Britain's...
deposits in the Chiungchussu formation, famous for their Konservat Lagerstätte
Lagerstätte
A Lagerstätte is a sedimentary deposit that exhibits extraordinary fossil richness or completeness.Palaeontologists distinguish two kinds....
n, or high number of fossils preserved in place. 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
Burgess Shale
The Burgess Shale Formation, located in the Canadian Rockies of British Columbia, is one of the world's most celebrated fossil fields, and the best of its kind. It is famous for the exceptional preservation of the soft parts of its fossils...
. They take their name from Maotianshan Hill in Chengjiang County
Chengjiang County
Chengjiang County is located in Yuxi, Yunnan Province, China, just north of Fuxian Lake....
, Yunnan
Yunnan
Yunnan is a province of the People's Republic of China, located in the far southwest of the country spanning approximately and with a population of 45.7 million . The capital of the province is Kunming. The province borders Burma, Laos, and Vietnam.Yunnan is situated in a mountainous area, with...
Province, China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
.
The most famous assemblage of organisms are referred to as the Chengjiang biota for the multiple scattered fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
sites in Chengjiang. The age of the Chengjiang Lagerstätte is locally termed Qiongzhusian, a stage indisputably correlated to the late Atdabanian Stage in Siberia
Siberia
Siberia is an extensive region constituting almost all of Northern Asia. Comprising the central and eastern portion of the Russian Federation, it was part of the Soviet Union from its beginning, as its predecessor states, the Tsardom of Russia and the Russian Empire, conquered it during the 16th...
n sequences of the middle of the Lower Cambrian. It dates to between 525 and 520 million years ago - a period situated in the middle of the early Cambrian epoch and at least some 10 million years older than the Burgess Shale. The shales also contain the slightly younger Guanshan biota.
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 naraoiidNaraoiidae
The Naraoiidae is a family of soft-shelled trilobite-like arthropods that are known only from the early and middle Cambrian -- primarily from the Burgess Shale of British Columbia and the Maotianshan Shale of China....
Misszhouia
Misszhouia
Misszhouia longicaudata is a species of blind, trilobite-like arthropod from the Cambrian period. In 1984 a well-preserved fossil of Misszhouia was discovered in the Maotianshan Shale; this discovery brought the shale to scientific attention.M...
, a soft-bodied relative of trilobite
Trilobite
Trilobites are a well-known fossil group of extinct marine arthropods that form the class Trilobita. The first appearance of trilobites in the fossil record defines the base of the Atdabanian stage of the Early Cambrian period , and they flourished throughout the lower Paleozoic era before...
s. Since then, the locality has been intensively studied by scientists from throughout the world, yielding a constant flow of new discoveries and triggering an extensive 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
Vetulicolia
VetulicoliaThe phylum name, Vetulocolia, is derived from the type genus, Vetulicola, which is a compound Latin word composed of vetuli, or "old," and cola, or "inhabitant." is an extinct phylum encompassing several Cambrian organisms...
of primitive deuterostomes.
The Chengjiang biota already 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 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
Proterozoic
The Proterozoic is a geological eon representing a period before the first abundant complex life on Earth. The name Proterozoic comes from the Greek "earlier life"...
-Phanerozoic
Phanerozoic
The Phanerozoic Eon is the current eon in the geologic timescale, and the one during which abundant animal life has existed. It covers roughly 542 million years and goes back to the time when diverse hard-shelled animals first appeared...
transition, and thus the fossil record’s best data source for understanding the apparently rapid diversification of life known as the Cambrian Explosion
Cambrian explosion
The Cambrian explosion or Cambrian radiation was the relatively rapid appearance, around , of most major phyla, as demonstrated in the fossil record, accompanied by major diversification of other organisms, including animals, phytoplankton, and calcimicrobes...
.
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 currentTurbidity current
A turbidity current is a current of rapidly moving, sediment-laden water moving down a slope through water, or another fluid. The current moves because it has a higher density and turbidity than the fluid through which it flows...
s, 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).
Trace fossils are abundant.
Chengjiang 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 trilobiteTrilobite
Trilobites are a well-known fossil group of extinct marine arthropods that form the class Trilobita. The first appearance of trilobites in the fossil record defines the base of the Atdabanian stage of the Early Cambrian period , and they flourished throughout the lower Paleozoic era before...
s, 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
Priapulida
Priapulida is a phylum of marine worms. They are named for their extensible spiny proboscis, which, in some species, may have a shape like that of a human penis...
(16 species) are also well represented. Other phyla represented are Brachiopoda, Chaetognatha
Chaetognatha
Chaetognatha, meaning hair-jaws, and commonly known as arrow worms, are a phylum of predatory marine worms that are a major component of plankton worldwide. About 20% of the known species are benthic, that is belonging to the lowest zone of the ocean, or benthic zone, and can attach to algae and...
, Cnidaria
Cnidaria
Cnidaria is a phylum containing over 9,000 species of animals found exclusively in aquatic and mostly marine environments. Their distinguishing feature is cnidocytes, specialized cells that they use mainly for capturing prey. Their bodies consist of mesoglea, a non-living jelly-like substance,...
, Ctenophora, Echinodermata, Hyolitha
Hyolitha
Hyolitha are enigmatic animals with small conical shells known from the Palaeozoic Era.-Shell morphology:The calcareous shells have a cover and two curved supports known as helens. Most are one to four centimeters in length and are triangular or elliptical in cross section...
, Nematomorpha
Nematomorpha
Nematomorpha is a phylum of parasitic animals that are superficially morphologically similar to nematode worms, hence the name. They range in size in most species from long and can reach in extreme cases up to 2 metres, and in diameter...
, 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
Lobopodia
Lobopodia is a group of poorly understood animals, which mostly fall as a stem group of arthropods. Their fossil range dates back to the Early Cambrian. Lobopods are segmented and typically bear legs with hooked claws on their ends....
, often considered a distinct phylum, with six genera represented: Luolishania, Paucipodia
Paucipodia
Paucipodia inermis is a lobopod known from the Lower Cambrian Chengjiang lagerstätte. Its gut is puzzling; in some places, it is preserved in three dimensions, infilled with sediment; whereas in others it may be flat...
, Cardiodictyon, Hallucigenia
Hallucigenia
Hallucigenia is an extinct genus of animal found as fossils in the Middle Cambrian-aged Burgess Shale formation of British Columbia, Canada, represented by the species H. sparsa, and in the Lower Cambrian Maotianshan shale of China, represented by the species H. fortis...
(also known from the Burgess Shale), Microdictyon
Microdictyon
Microdictyon is an extinct "armored worm" coated with dot-likescleritic scales, known from the Early CambrianMaotianshan shale of Yunnan China. Microdictyon is sometimes included...
, 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
Myllokunmingia
Myllokunmingia is a chordate from the Lower Cambrian Maotianshan shales of China, thought to be a vertebrate, although this is not conclusively proven. It is 28 mm long and 6 mm high....
, possibly a very primitive agnathid (i.e., jawless fish). Similar to Myllokunmingia is Haikouichthys
Haikouichthys
Haikouichthys is an extinct genus of craniate believed to have lived c. 530 million years ago, during the Cambrian explosion of multicellular life...
ercaicunensis, another primitive fish-like animal.
The enigmatic Yunnanozoon lividum
Yunnanozoon
Yunnanozoon lividum is a suspected a hemichordate or chordate from the Lower Cambrian, Chengjiang biota of Yunnan province, China....
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
Notochord
The notochord is a flexible, rod-shaped body found in embryos of all chordates. It is composed of cells derived from the mesoderm and defines the primitive axis of the embryo. In some chordates, it persists throughout life as the main axial support of the body, while in most vertebrates it becomes...
(neural chord).
At present, there is no agreement as to the systematic placement of the Vetulicola
Vetulicola
Vetulicola is a genus of small, Early Cambrian animals from the Chengjiang biota of China.-Description:The type species, Vetulicola cuneata has a body composed of two distinct parts of approximately equal length. The front part is rectangular with a carapace-like structure of four rigid cuticular...
, represented by seven species from Chengjiang: originally described as crustacean arthropods, the Vetulicola were later erected as a new phylum of primitive deuterostome
Deuterostome
Deuterostomes are a superphylum of animals. They are a subtaxon of the Bilateria branch of the subregnum Eumetazoa, and are opposed to the protostomes...
s 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
Anomalocaris
Anomalocaris is an extinct genus of anomalocaridid, which are, in turn, thought to be closely related to the arthropods. The first fossils of Anomalocaris were discovered in the Ogygopsis Shale by Joseph Frederick Whiteaves, with more examples found by Charles Doolittle Walcott in the famed...
saron, the alleged predatory terror of the early Cambrian, is the most famous. Shu (2006) recently described Stromatoveris
Stromatoveris
Stromatoveris is a genus of Cambrian ctenophore? fossil from Chengjiang deposits of Yunnan that was originally aligned with the fossil Charnia from the Ediacara biota. However, such an affinity is developmentally implausible....
psygmoglena as a possible bilateran
Bilateria
The bilateria are all animals having a bilateral symmetry, i.e. they have a front and a back end, as well as an upside and downside. Radially symmetrical animals like jellyfish have a topside and downside, but no front and back...
missing link between Ediacaran
Ediacaran
The Ediacaran Period , named after the Ediacara Hills of South Australia, is the last geological period of the Neoproterozoic Era and of the Proterozoic Eon, immediately preceding the Cambrian Period, the first period of the Paleozoic Era and of the Phanerozoic Eon...
fronds and Cambrian ctenophore
Ctenophore
The Ctenophora are a phylum of animals that live in marine waters worldwide. Their most distinctive feature is the "combs", groups of cilia that they use for swimming, and they are the largest animals that swim by means of cilia – adults of various species range from a few millimeters to in size...
s.
See also
- Geography of ChinaGeography of ChinaChina stretches some across the East Asian landmass bordering the East China Sea, Korea Bay, Yellow Sea, and South China Sea, between North Korea and Vietnam in a changing configuration of broad plains, expansive deserts, and lofty mountain ranges, including vast areas of inhospitable terrain...
- Stephen Jay GouldStephen Jay GouldStephen Jay Gould was an American paleontologist, evolutionary biologist, and historian of science. He was also one of the most influential and widely read writers of popular science of his generation....
, Wonderful LifeWonderful Life (book)Wonderful Life: The Burgess Shale and the Nature of History is a book on the evolution of Cambrian fauna by Harvard paleontologist Stephen Jay Gould...
External links
- http://www.fossilmuseum.net/Fossil_Sites/Chengjiang/Chengjiang-Biota.htm