Haikouichthys /ˌhaɪkuːˈɪkθɪs/ is an extinct genus of craniate (animals with notochords and distinct heads) believed to have lived 525 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.