Jawed Fish:
* Placodermi: These were armored fish with bony plates covering their head and front part of their body. They were apex predators of the Devonian.
* Acanthodii: These were small, spiny-finned fish with sharp teeth and a jaw, sometimes referred to as "spiny sharks".
* Chondrichthyes: This group includes modern sharks, rays, and chimaeras. They evolved from placoderms and were characterized by cartilaginous skeletons.
* Osteichthyes: This group includes all bony fish, which are the most diverse group of vertebrates today. The first bony fish appeared in the Devonian.
Jawless Fish:
* Agnatha: This group includes modern lampreys and hagfish. They lack jaws and have a cartilaginous skeleton. Agnathans were already present before the Devonian, but continued to evolve and diversify during this period.
Other notable fish:
* Lungfish: These fish were able to breathe air, which allowed them to survive in shallow waters and even on land for short periods.
* Crossopterygii: This group includes the ancestors of tetrapods, the first animals to walk on land. They possessed fleshy fins and could breathe air.
The Devonian period is considered a pivotal time in fish evolution, as it saw the emergence of many important groups that still exist today. It was during this period that the basic body plan of many modern fish was established.