Haikouichthys

Haikouichthys Temporal range: Cambrian Stage 3, 518 Ma[1] PreꞒ Ꞓ O S D C P T J K Pg N ↓
Restoration
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Order:	†Myllokunmingiida
Family:	†Myllokunmingiidae
Genus:	†Haikouichthys Luo et al., 1999
Species:	†H. ercaicunensis
Binomial name
†Haikouichthys ercaicunensis Luo et al., 1999

Haikouichthys /ˌhaɪkuˈɪkθɪs/ is an extinct genus of craniate (animals with notochords and distinct heads) that lived 518 million years ago, during the Cambrian explosion of multicellular life. The type species, Haikouichthys ercaicunensis, was first described in 1999.^[2] 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 indicates that the animal is probably a basal stem-craniate.^[3] Some researchers have considered Haikouichthys to be synonymous with the other primitive chordate Myllokunmingia,^[4] 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,^[5] the absence of branchial rays in Myllokunmingia and the myomeres having a more acute shape in Haikouichthys.^[6]