''Haikouichthys'' is an extinct
genus
Genus ( plural genera ) is a taxonomic rank used in the biological classification of living and fossil organisms as well as viruses. In the hierarchy of biological classification, genus comes above species and below family. In binomial nom ...
of
craniate (animals with
notochord
In anatomy, the notochord is a flexible rod which is similar in structure to the stiffer cartilage. If a species has a notochord at any stage of its life cycle (along with 4 other features), it is, by definition, a chordate. The notochord consi ...
s and distinct heads) that lived 518 million years ago, during the
Cambrian explosion
The Cambrian explosion, Cambrian radiation, Cambrian diversification, or the Biological Big Bang refers to an interval of time approximately in the Cambrian Period when practically all major animal phyla started appearing in the fossil record. ...
of multicellular life. ''Haikouichthys'' had a defined skull and other characteristics that have led
paleontologists
Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of foss ...
to label it a true craniate, and even to be popularly characterized as one of the
earliest fishes.
Cladistic analysis
Cladistics (; ) is an approach to biological classification in which organisms are categorized in groups ("clades") based on hypotheses of most recent common ancestry. The evidence for hypothesized relationships is typically shared derived chara ...
indicates that the animal is probably a basal
chordate
A chordate () is an animal of the phylum Chordata (). All chordates possess, at some point during their larval or adult stages, five synapomorphies, or primary physical characteristics, that distinguish them from all the other taxa. These fi ...
or a basal
craniate;
but it does not possess sufficient features to be included uncontroversially even in either
stem group
In phylogenetics, the crown group or crown assemblage is a collection of species composed of the living representatives of the collection, the most recent common ancestor of the collection, and all descendants of the most recent common ancestor. ...
.
It was formally described in 1999.
Description
''Haikouichthys'' is about long and is narrower than ''
Myllokunmingia
''Myllokunmingia'' is a genus of basal chordate from the Lower Cambrian Maotianshan shales of China 518 to 490 mya and is thought to be a vertebrate, although this is not conclusively proven. The species M. fengjiaoa is 28 mm long and 6&nbs ...
'', another
putative chordate
A chordate () is an animal of the phylum Chordata (). All chordates possess, at some point during their larval or adult stages, five synapomorphies, or primary physical characteristics, that distinguish them from all the other taxa. These fi ...
that comes from the same beds. The
holotype
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 seve ...
of ''Haikouichthys ercaicunensis'' was found in the Yuansshan member of the
Qiongzhusi Formation in the 'Eoredlichia' Zone near Haikou at Ercaicun,
Kunming City
Kunming (; ), also known as Yunnan-Fu, is the capital and largest city of Yunnan province, China. It is the political, economic, communications and cultural centre of the province as well as the seat of the provincial government. The headquar ...
,
Yunnan
Yunnan , () is a landlocked province in the southwest of the People's Republic of China. The province spans approximately and has a population of 48.3 million (as of 2018). The capital of the province is Kunming. The province borders the ...
, China,
[ hence its name "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.BBC News "Oldest fossil fish caught", 4 November 1999]
/ref> Following the discovery of the holotype, additional Lower Cambrian fossils of ''Haikouichthys ercaicunensis'' have been discovered.
The animal has a distinct head and tail. The head has at least six and perhaps nine probable gill
A gill () is a respiratory organ that many 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 respiration on land provided they ar ...
s. There are a number of segments (myomeres) with rear directed chevrons in the tail. There is a notochord
In anatomy, the notochord is a flexible rod which is similar in structure to the stiffer cartilage. If a species has a notochord at any stage of its life cycle (along with 4 other features), it is, by definition, a chordate. The notochord consi ...
. There is a prominent dorsal fin with fin radials similar, but not comparable, to those of hagfish
Hagfish, of the class Myxini (also known as Hyperotreti) and order Myxiniformes , are eel-shaped, slime-producing marine fish (occasionally called slime eels). They are the only known living animals that have a skull but no vertebral column, ...
and lamprey
Lampreys (sometimes inaccurately called lamprey eels) are an ancient extant lineage of jawless fish of the order Petromyzontiformes , placed in the superclass Cyclostomata. The adult lamprey may be characterized by a toothed, funnel-like s ...
s. The fin radials seem to angle "forward" toward the end thought on the basis of internal structures to be the head. This happens with a few modern fish but is an uncommon arrangement. There are 13 circular structures along the bottom that may be gonad
A gonad, sex gland, or reproductive gland is a mixed gland that produces the gametes and sex hormones of an organism. Female reproductive cells are egg cells, and male reproductive cells are sperm. The male gonad, the testicle, produces sp ...
s, slime organs, or something else entirely.
See also
* Ostracoderm
Ostracoderms () are the armored jawless fish of the Paleozoic Era. The term does not often appear in classifications today because it is paraphyletic (excluding jawed fishes) (may also be polyphyletic if anaspids are closer to cyclostomes) and ...
* ''Arandaspis
''Arandaspis prionotolepis'' is an extinct species of jawless fish that lived in the Ordovician period, about 480 to 470 million years ago. Its remains were found in the Stairway Sandstone near Alice Springs, Australia in 1959, but it was not d ...
''
* ''Pikaia
''Pikaia gracilens'' is an extinct, primitive chordate animal known from the Middle Cambrian Burgess Shale of British Columbia. Described in 1911 by Charles Doolittle Walcott as an annelid, and in 1979 by Harry B. Whittington and Simon Conway ...
'' – Cambrian chordate
* ''Myllokunmingia
''Myllokunmingia'' is a genus of basal chordate from the Lower Cambrian Maotianshan shales of China 518 to 490 mya and is thought to be a vertebrate, although this is not conclusively proven. The species M. fengjiaoa is 28 mm long and 6&nbs ...
'' – close relative
* ''Zhongjianichthys
''Zhongjianichthys rostratus'' is an extinct basal chordate that lived in the Cambrian period, approximately 518 million years ago. It is sometimes regarded as an early fish, and therefore as one of the first vertebrates. ''Zhongjianichthys'' is ...
'' – eel-like close relative
* ''Lancelet
The lancelets ( or ), also known as amphioxi (singular: amphioxus ), consist of some 30 to 35 species of "fish-like" benthic filter feeding chordates in the order Amphioxiformes. They are the modern representatives of the subphylum Cephalochord ...
'' – living animal with similar morphology
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