The jaw is invented
A gill arch becomes something that can bite
See it on the timeline →In depth
Fossils from the Xiaoxiang fauna in Yunnan have pushed the origin of jawed vertebrates significantly further back and shown that the modern major groups diverged earlier than assumed. Embryology reveals the origin directly: the jaw develops from the same cell population as the gill arches, governed by the same genes. Jaws made predation efficient enough to reshape marine ecology, culminating in the Devonian with armoured fish such as Dunkleosteus, up to six metres long. Every jawed vertebrate, you included, inherits that rebuilt gill arch.
For children
The first fish had only a hole to suck food through. Then the front gill arch was bent and strengthened, becoming a jaw that could grip and bite. Suddenly fish could hunt large prey — and everyone else had to get faster or better armoured.
Connects to
Part of Terra Saga — the story of Earth on a timeline. terrasaga.org