Haikouichthys: the first fish, the first vertebrates
What happened
Among the Chengjiang biota's fossils is Haikouichthys, a slender, two-and-a-half-centimetre animal that the Natural History Museum lists among the earliest vertebrates in the fossil record. Its impression shows a notochord, the flexible internal supporting rod that is a hallmark of all chordates, along with what appear to be traces of a skull and vertebral elements, features that put it on the vertebrate branch of the family tree rather than merely near it. It shared its Chengjiang world with the earlier-discovered, less fish-like Pikaia, but Haikouichthys and its close relative Myllokunmingia, both from Chengjiang, show more developed vertebrate anatomy and are considered closer to the actual root of the vertebrate lineage.
Why it matters
Every vertebrate alive, every fish, amphibian, reptile, bird, and mammal, including humans, descends from an animal built along the same basic plan Haikouichthys already shows in the Cambrian. It is one of the plainest physical links between the Cambrian explosion and our own existence.
How we know
The classification as a vertebrate rests on preserved anatomical details in the fossil impression itself, the notochord, evidence of a skull, and vertebral elements, compared directly against the same structures in living jawless fish, the closest modern relatives to what Haikouichthys is believed to have been.
Sources
- Natural History Museum, London. Prehistoric fish: 11 of the largest, weirdest and most significant · Reputable sourcenhm.ac.uk · The domain "nhm.ac.uk" is on our Reputable source registry. · Link is live and its text matches the event's key terms (Jul 2026)
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Related timelines
- Human Evolution → · The start of the vertebrate lineage human evolution eventually follows