''Haikouichthys'' is an extinct
genus of
craniate (animals with
notochord
In anatomy, the notochord is a flexible rod which is similar in structure to the stiffer cartilage. If a species has a notochord at any stage of its life cycle (along with 4 other features), it is, by definition, a chordate. The notochord consis ...
s and distinct heads) that lived 518 million years ago, during the
Cambrian explosion
The Cambrian explosion, Cambrian radiation, Cambrian diversification, or the Biological Big Bang refers to an interval of time approximately in the Cambrian Period when practically all major animal phyla started appearing in the fossil recor ...
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.
It was formally described in 1999.
Description
''Haikouichthys'' is about long and is narrower than ''
Myllokunmingia'', another
