''Haikouichthys'' is an extinct

genus Genus (; : genera ) is a taxonomic rank above species and below family (taxonomy), family as used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In bino ...

of craniate (animals with

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 ...

s and distinct heads) that lived 518 million years ago, during the Cambrian explosion of multicellular life. 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 ...

, ''Haikouichthys ercaicunensis'', was first described in 1999. ''Haikouichthys'' had a defined skull and other characteristics that have led paleontologists to label it a true craniate, and even to be popularly characterized as one of the earliest fishes. More than 500 specimens were referred to this taxon and

phylogenetic analyses In biology, phylogenetics () is the study of the evolutionary history of life using observable characteristics of organisms (or genes), which is known as Computational phylogenetics, phylogenetic inference. It infers the relationship among organ ...

indicates that the animal is probably a basal stem- craniate. Some researchers have considered ''Haikouichthys'' to be synonymous with the other primitive chordate '' Myllokunmingia'', 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''.

Description

''Haikouichthys'' is about long and is narrower than '' Myllokunmingia'', another putative

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 ...

that comes from the same beds. 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 ...

of ''Haikouichthys ercaicunensis'' was found in the Yuanshan member of the Qiongzhusi Formation in the 'Eoredlichia' Zone near Ercai

Village A village is a human settlement or community, larger than a hamlet but smaller than a town with a population typically ranging from a few hundred to a few thousand. Although villages are often located in rural areas, the term urban v ...

in the Haikou

Subdistrict A subdistrict or sub-district is an administrative division that is generally smaller than a district. Equivalents * Administrative posts of East Timor, formerly Portuguese-language * Kelurahan, in Indonesia * Mukim, a township in Brunei, Ind ...

(not to be confused with the city of

Haikou Haikou; Chinese postal romanization, formerly romanized as Hoihow is the capital city, capital and most populous city of the Chinese province of Hainan. Haikou city is situated on the northern coast of Hainan, by the mouth of the Nandu River. ...

Hainan Hainan is an island provinces of China, province and the southernmost province of China. It consists of the eponymous Hainan Island and various smaller islands in the South China Sea under the province's administration. The name literally mean ...

) of Xishan, Kunming, hence its name, which means "Haikou fish from Ercaicun". The fossil was recovered among the Chengjiang fauna, in one of a series of Lagerstätten sites where thousands of exquisitely preserved soft-bodied fossils have already been found. Following the discovery of the holotype, additional Lower Cambrian fossils of ''Haikouichthys ercaicunensis'' have been discovered. Haikouichthys4

Researchers have identified eyes, cranial cartilages, at least six to nine gill arches, possible nasal sacs and otic capsules from its head. It is likely that the brain of ''Haikouichthys'' had the same major brain divisions found in extant vertebrates. The describers of this taxon initially reported its potential

, though some researchers consider this claim to be uncertain. Still, numerous segments (myomeres) with rear directed chevrons in the tail indicate that ''Haikouichthys'' was indeed a chordate, and complete

dorsal Dorsal (from Latin ''dorsum'' ‘back’) may refer to: * Dorsal (anatomy), an anatomical term of location referring to the back or upper side of an organism or parts of an organism * Dorsal, positioned on top of an aircraft's fuselage The fus ...

ventral Standard anatomical terms of location are used to describe unambiguously the anatomy of humans and other animals. The terms, typically derived from Latin or Greek roots, describe something in its standard anatomical position. This position prov ...

and

caudal fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only ...

s were also found in its specimens. The fin radials of ''Haikouichthys'' show similarity to those of

hagfish Hagfish, of the Class (biology), class Myxini (also known as Hyperotreti) and Order (biology), order Myxiniformes , are eel-shaped Agnatha, jawless fish (occasionally called slime eels). Hagfish are the only known living Animal, animals that h ...

and

lamprey Lampreys (sometimes inaccurately called lamprey eels) are a group of Agnatha, jawless fish comprising the order (biology), order Petromyzontiformes , sole order in the Class (biology), class Petromyzontida. The adult lamprey is characterize ...

s, and they seem to angle "forward" toward the end thought on the basis of internal structures to be the head. There are 13 circular structures along the bottom that may be

gonad A gonad, sex gland, or reproductive gland is a Heterocrine gland, mixed gland and sex organ that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gon ...

s, slime organs, or something else entirely.

References

External links

Oldest fish fossil caught
{{Taxonbar, from=Q285132 Maotianshan shales fossils Prehistoric jawless fish genera Fossil taxa described in 1999 Cambrian fish Cambrian genus first appearances Cambrian genus extinctions Cambrian chordates

Description

See also

References

External links