Haikouichthys was a Cambrian chordate from China. It is often identified as one of the earliest fishes.


Haikouichthys measured about 2.5 centimeters long, and most probably had a notochord. It also had fins that resemble those of modern lampreys or hagfish.[1]



Haikouichthys as it appeared in Walking with Monsters

Cladistic analysis has revealed that Haikouichthys is most likely a basal craniate, although this classification is not without controversy.[2]


Haikouichthys was first found in the Qiongzhusi Formation of China,[3] as part of the Chengjiang fauna.[4] It was described as Haikouichthys ercaicunensis in 1999.

In popular cultureEdit

Haikouichthys appeared in the 2003 BBC documentary Walking with Monsters, where it was depicted as the ancestor of all known vertebrates.


  1. 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, PMID 15312089
  2. Donoghue, P.C.J.; Purnell, M.A. (2005), "Genome duplication, extinction and vertebrate evolution", Trends in Ecology & Evolution 20 (6): 312–319, doi:10.1016/j.tree.2005.04.008, PMID 16701387
  3. 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, Bibcode 2003Natur.421..526S, doi:10.1038/nature01264, ISSN 0028-0836, PMID 12556891
  4. BBC News "Oldest fossil fish caught", 4 November 1999