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Haikouichthys; Fossil range: 535–520 Ma PreЄ Є O S D C P T J K Pg N
	Artist's concept of Haikouichthys ercaicunensis
Scientific classification
Kingdom:	Animalia;
Phylum:	Chordata;
(unranked):	Craniata;
Family:	Myllokunmingiidae;
Genus:	Haikouichthys;
Species:	Haikouichthys ercaicunensis; Luo, Hu & Shu.

Paleontology portal

Haikouichthys is an extinct genus of craniate (creatures with backbones and distinct heads) believed to have lived c. 530 million years ago, during the Cambrian explosion. 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 fish,^[1] but it does not possess sufficient features to be included uncontroversially even in the stem group.^[2]

[edit] Description

Cladistic analysis indicates that the animal is probably a basal chordate, or a basal craniate. ^[3] It is about 2.5 cm long and is narrower than Myllokunmingia, another putative chordate that comes from the same beds. The holotype was found in the Yuansshan member of the Qiongzhusi Formation in the 'Eoredlichia' Zone near Haikou at Ercaicun, Kunming City, Yunnan, China.^[1]

The animal has a distinct head and tail. The head has at least six and perhaps nine probable gills. There are a number of segments (myomeres) with rear directed chevrons in the tail. There is probably a notochord although only a short segment is preserved in the single known specimen. There is a prominent dorsal fin with fin radials similar, but not comparable, to those of hagfish and lampreys.^[4] 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 gonads, slime organs, or something else entirely.

[edit] See also

Ostracoderm
Arandaspis
Pikaia Cambrian chordate
Myllokunmingia close relative
Zhongjianichthys eel-like close relative

[edit] External links

See the following web sites for more information and pictures:
- http://www.sciencenews.org/sn_arc99/11_6_99/fob1.htm
- http://news.bbc.co.uk/1/hi/sci/tech/504776.stm

[edit] References

^ ^a ^b Shu, D. G.; Morris, S. C.; Han, J.; Zhang, Z. F.; Yasui, K.; Janvier, P.; Chen, L.; Zhang, X. L. et al. (Jan 2003), "Head and backbone of the Early Cambrian vertebrate Haikouichthys", Nature 421 (6922): 526–529, doi:10.1038/nature01264, ISSN 0028-0836, PMID 12556891, http://adsabs.harvard.edu/abs/2003Natur.421..526S edit
^ Donoghue, P.C.J.; Purnell, M.A. (2005), "Genome duplication, extinction and vertebrate evolution", Trends in Ecology & Evolution 20 (6): 312–319, http://palaeo.gly.bris.ac.uk/Publs/donoghue/Donoghue_and_Purnell_2005.pdf
^ http://www.palaeos.com/Paleozoic/Cambrian/Cambrian.2.html
^ Zhang, X.G.; Hou, X.G. (2004), "Evidence for a single median fin-fold and tail in the Lower Cambrian vertebrate, Haikouichthys ercaicunensis", Journal of Evolutionary Biology 17 (5): 1162–1166, doi:10.1111/j.1420-9101.2004.00741.x

CAMPBELL, NEIL A. & REECE, JANE B. (2005). Biology, Seventh Edition. San Francisco CA: Benjamin Cummings.

[Shu2003-0] Shu, D. G.; Morris, S. C.; Han, J.; Zhang, Z. F.; Yasui, K.; Janvier, P.; Chen, L.; Zhang, X. L. et al. (Jan 2003), "Head and backbone of the Early Cambrian vertebrate Haikouichthys", Nature 421 (6922): 526–529, doi:10.1038/nature01264, ISSN 0028-0836, PMID 12556891, http://adsabs.harvard.edu/abs/2003Natur.421..526S edit

[Donoghue2005-1] Donoghue, P.C.J.; Purnell, M.A. (2005), "Genome duplication, extinction and vertebrate evolution", Trends in Ecology & Evolution 20 (6): 312–319, http://palaeo.gly.bris.ac.uk/Publs/donoghue/Donoghue_and_Purnell_2005.pdf

[2] ttp://www.palaeos.com/Paleozoic/Cambrian/Cambrian.2.html

[Zhang2004-3] Zhang, X.G.; Hou, X.G. (2004), "Evidence for a single median fin-fold and tail in the Lower Cambrian vertebrate, Haikouichthys ercaicunensis", Journal of Evolutionary Biology 17 (5): 1162–1166, doi:10.1111/j.1420-9101.2004.00741.x

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Contents

[edit] Description

[edit] See also

[edit] External links

[edit] References