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. It is among the oldest possible craniates, found in the lower Cambrian Chengjiang (524 million years ago). It appears to have a skull and skeletal structures made of cartilage. There is no sign of mineralization of the skeletal elements (biomineralization). The holotype was found in the Yuanshan member of the Qiongzhusi Formation in the Eoredlichia Zone near Haikou at Ercaicun, Kunming City, Yunnan, China. The animal has a distinct head and trunk with a forward sail-like (1.5 mm) dorsal fin and a ventral fin fold (probably paired) further back. The head has five or six gill pouches with hemibranchs. There are 25 segments (myomeres) with rearward chevrons in the trunk. There is a notochord, a pharynx and digestive tract that may run all the way to the rear tip of the animal. The mouth cannot be clearly identified. There may be a pericardic cavity. There are no fin radials. There is only one specimen, which has the tip of the tail buried in sediment. Only one species is known Ц Myllokunmingia fengjiaoa (Shu, Zhang & Han). Related creatures are Haikouichthys and Zhongjianichthys. The Maotianshan Shales are a series of lower Cambrian deposits in the Chiungchussu formation, famous for their Konservat Lagerstatten, 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. They take their name from Maotianshan Hill (Chinese: ?; pinyin: Maotianshan) in Chengjiang County, Yunnan Province, China. The most famous assemblage of organisms are referred to as the Chengjiang biota for the multiple scattered fossil sites in Chengjiang. The age of the Chengjiang Lagerstatte is locally termed Qiongzhusian, a stage indisputably correlated to the late Atdabanian Stage in Siberian 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. A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of several such, but explicitly designated as the holotype. Under the ICZN, a holotype is one of several kinds of name-bearing types. An isotype is a duplicate of the holotype. For example, the holotype for the butterfly Lycaeides idas longinus is a preserved specimen of that species, held by the Museum of Comparative Zoology at Harvard University. A holotype is not necessarily 'typical' of that taxon, although ideally it should be. Sometimes just a fragment of an organism is the holotype, for example in the case of a fossil. The holotype of Pelorosaurus humerocristatus, a large herbivore dinosaur from the early Jurassic period, is a fossil leg bone stored at the Natural History Museum in London. Even if a better specimen is subsequently found, the holotype is not superseded. In the absence of a holotype (e.g. it was lost) another type may be selected, out of a range of different kinds of type, depending on the case. Note that in the ICBN and ICZN the definitions of types are similar in intent but not identical in terminology or underlying concept. For example in both the ICBN and the ICZN a "neotype" is a type that was later appointed in the absence of the original holotype. Additionally, under the ICZN the Commission is empowered to replace a holotype with a "neotype", when the holotype turns out to lack important diagnostic features needed to distinguish the species from its close relatives. For example, the crocodile-like archosaurian reptile Parasuchus hislopi Lydekker, 1885 was described based on a premaxillary rostrum (part of the snout), but this is no longer sufficient to distinguish Parasuchus from its close relatives. This made the name Parasuchus hislopi a nomen dubium. Texan paleontologist Sankar Chatterjee proposed that a new type specimen, a complete skeleton, be designated. The International Commission on Zoological Nomenclature considered the case and agreed to replace the original type specimen with the proposed neotype.