''Myllokunmingia'' is a genus of basal

chordate A chordate ( ) is a bilaterian animal belonging to the phylum Chordata ( ). All chordates possess, at some point during their larval or adult stages, five distinctive physical characteristics ( synapomorphies) that distinguish them from ot ...

from the Lower

Cambrian The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...

Maotianshan shales The Maotianshan Shales () are a series of Early Cambrian sedimentary deposits in the Chiungchussu Formation or Heilinpu Formation, famous for their '' Konservat Lagerstätten'', deposits known for the exceptional preservation of fossilized orga ...

China China, officially the People's Republic of China (PRC), is a country in East Asia. With population of China, a population exceeding 1.4 billion, it is the list of countries by population (United Nations), second-most populous country after ...

518 mya and is thought to be a

vertebrate Vertebrates () are animals with a vertebral column (backbone or spine), and a cranium, or skull. The vertebral column surrounds and protects the spinal cord, while the cranium protects the brain. The vertebrates make up the subphylum Vertebra ...

, although this is not conclusively supported. The

type species In International_Code_of_Zoological_Nomenclature, zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the spe ...

''M. fengjiaoa'' is 28 mm long and 6 mm high. It is among the oldest possible craniates, found in the lower Cambrian Chengjiang (). It appears to have a

skull The skull, or cranium, is typically a bony enclosure around the brain of a vertebrate. In some fish, and amphibians, the skull is of cartilage. The skull is at the head end of the vertebrate. In the human, the skull comprises two prominent ...

and skeletal structures made of

cartilage Cartilage is a resilient and smooth type of connective tissue. Semi-transparent and non-porous, it is usually covered by a tough and fibrous membrane called perichondrium. In tetrapods, it covers and protects the ends of long bones at the joints ...

. There is no sign of

biomineralization Biomineralization, also written biomineralisation, is the process by which living organisms produce minerals, often resulting in hardened or stiffened '' mineralized tissues''. It is an extremely widespread phenomenon: all six taxonomic kingd ...

of the skeletal elements. The

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

was found in the Yuanshan member of the Qiongzhusi Formation in the Eoredlichia Zone near Haikou at Ercaicun, Kunming City,

Yunnan Yunnan; is an inland Provinces of China, province in Southwestern China. The province spans approximately and has a population of 47.2 million (as of 2020). The capital of the province is Kunming. The province borders the Chinese provinces ...

, China. Some researchers have considered the other primitive chordate '' Haikouichthys'' to be synonymous with this taxon, but subsequent studies led by the British paleontologist Simon Conway Morris identified both genera to be distinct, separate taxa on the basis of different gill arrangement, the absence of branchial rays in ''Myllokunmingia'' and the myomeres having a more acute shape in ''Haikouichthys''. The animal has a distinct head and trunk with a forward sail-like (1.5 mm)

dorsal fin A dorsal fin is a fin on the back of most marine and freshwater vertebrates. Dorsal fins have evolved independently several times through convergent evolution adapting to marine environments, so the fins are not all homologous. They are found ...

and a ventral finfold (probably paired) further back. The maximum height of ''M. fengjiaoa'' is at 6mm. The maximum height point is located around 11mm from the anterior. The head has five or six

gill A gill () is a respiration organ, respiratory organ that many aquatic ecosystem, aquatic organisms use to extract dissolved oxygen from water and to excrete carbon dioxide. The gills of some species, such as hermit crabs, have adapted to allow r ...

pouches with hemibranchs. In the trunk there are 25 segments ( myomeres) with rearward-facing chevrons. There is a

notochord The notochord is an elastic, rod-like structure found in chordates. In vertebrates the notochord is an embryonic structure that disintegrates, as the vertebrae develop, to become the nucleus pulposus in the intervertebral discs of the verteb ...

, a

pharynx The pharynx (: pharynges) is the part of the throat behind the human mouth, mouth and nasal cavity, and above the esophagus and trachea (the tubes going down to the stomach and the lungs respectively). It is found in vertebrates and invertebrates ...

and a

digestive tract The gastrointestinal tract (GI tract, digestive tract, alimentary canal) is the tract or passageway of the Digestion, digestive system that leads from the mouth to the anus. The tract is the largest of the body's systems, after the cardiovascula ...

that may run all the way to the rear tip of the animal. The mouth cannot be clearly identified. There may be a pericardial cavity. There are no fin radials on M. fengjiaoa. There is only one specimen, which has the tip of the tail buried in

sediment Sediment is a solid material that is transported to a new location where it is deposited. It occurs naturally and, through the processes of weathering and erosion, is broken down and subsequently sediment transport, transported by the action of ...

References

External links

* http://www.sciencenews.org/sn_arc99/11_6_99/fob1.htm * https://web.archive.org/web/20030511135309/http://www.gs-rc.org/repo/repoe.htm
Lower Cambrian vertebrates from south China

Oldest fossil fish caught
Prehistoric jawless fish genera Maotianshan shales fossils Cambrian fish {{cambrian-animal-stub la:Myllokunmingia fengjiaoa Cambrian chordates Cambrian genus extinctions

See also

References

External links