Although the dominant creatures of the Cambrian period were the armored arthropods, it gave rise to the beginning of one of the most successful types of animals-the vertebrates. And one of the very first was the tiny fish Haikouicthys. Existing among the giant predators like Anomalocaris, this tiny fish had to find other ways to survive in the harsh Cambrian seas. These fish were some of our earliest ancestors.

Basic info

Meaning of Name: Haikouicthys means "fish from Haikou, Kunming".

Time of existence: Haikouicthys lived during the early Cambrian period, about 518 million to 530 million years ago.

Diet: Haikouicthys was most likely a scavenger, as their small size would not enable them to hunt most of the other creatures that they inhabited the seas with. They would most likely scavenge the leftovers of big predators like Anomalocaris, and occasionally even scavenge off of them.

Threats: Haikouicthys shared the sea with many large arthropods, and were most likely seen as prey by most of them.

Size: Haikouicthys was only about an inch long, no bigger than the average thumbnail.

A group of Haikouicthys

Attributes: Haikouicthys' best attribute is its strong backbone, which makes it much more manuverable than its arthropod enemies, and allows them to move more fluidly.

Haikouicthys swimming

Appearances in the Walking With... series

Walking with Monsters

Episode 1-Water Dwellers

A small group of Haikouicthys is first seen swimming above a trilobite garden where the Anomalocaris is feeding.  After the Anomalocaris is injured during a fight, a school of Haikouicthys take notice.

A school of Haikouicthys

They begin to scavenge the wound, while the Anomalocaris attempts to ward them off.  We also get information that they are our earliest known ancestor, as they have developed a primitive backbone.  Eventually, the arthropod swims off, as the school of Haikouicthys follow him.  Eventually, the Haikouicthys begins to evolve, with the muscles near its backbone turning into a tail, fins appearing, and evolving a distinct head.  One individual is seen going through this evolution, where he evolves into another type of fish called Cephalaspis.

Haikouicthys' tail evolving

Haikouicthys' head evolving

Haikouicthys evolving into Cephalaspis