During the Paleozoic Era, there was a period called the Devonian Period.
The Devonian Period was first studied with a Devonian red sandstone found in an area called Devon, England; this is the reason why the period was named Devonian.
This period is known for the development of thousands of ancient fish species.
Interestingly enough, during these early stages of fish development, they did not have jaws, and their bodies were comprised of cartilage, like the modern day shark.