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 of multicellular life. 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. Cladistic analysis indicates that the animal is probably a basal chordate or a basal craniate; but it does not possess sufficient features to be included uncontroversially even in either stem group.
The holotype of Haikouichthys ercaicunensis was found in the Yuansshan member of the Qiongzhusi Formation in the 'Eoredlichia' Zone near Haikou at Ercaicun, Kunming City, Yunnan, 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.
