Haikouichthys (Wikimedia Commons).


Haikouichthys (Greek for "fish from Haikou"); pronounced HIGH-koo-ICK-thiss


Shallow seas of Asia

Historical Period:

Early Cambrian (530 million years ago)

Size and Weight:

About one inch long and less than an ounce


Small marine organisms

Distinguishing Characteristics:

Tiny size; fin along length of back

About Haikouichthys

The Cambrian period is famous for its "explosion" of bizarre invertebrate life forms, but this span of time also saw the evolution of the earliest almost-vertebrates--marine organisms like Haikouichthys, Pikaia and Myllokunmingia that bore the faintest outlines of backbones and had a noticeably fish-like shape.

As with these other genera, whether or not Haikouichthys was technically a prehistoric fish is still a subject of debate. This was certainly one of the earliest craniates (i.e., organisms with skulls), but lacking any definitive fossil evidence, it may have had a primitive "notochord" running down its back rather than a true backbone.

Haikouichthys and its companions did, however, introduce some features that are so commonplace now as to be completely unremarkable. For example, this creature's head was distinct from its tail, it was bilaterally symmetric (that is, its right side matched up with its left side), and it had two eyes and a mouth on its "head" end. By Cambrian standards, it may have been the most advanced life form of its day!

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Strauss, Bob. "Haikouichthys." ThoughtCo, Apr. 5, 2023, thoughtco.com/overview-of-haikouichthys-1093670. Strauss, Bob. (2023, April 5). Haikouichthys. Retrieved from https://www.thoughtco.com/overview-of-haikouichthys-1093670 Strauss, Bob. "Haikouichthys." ThoughtCo. https://www.thoughtco.com/overview-of-haikouichthys-1093670 (accessed May 28, 2023).