It wasn't until the end of this period that they started to decline again, most likely because of the appearance of jawed fish.

Placoderms were among the first jawed fish, the Gnathostomata.

A century later, Eric Stensiö showed that placoderms were genuine jawed fish.

The relationship between the placoderm and other jawed fish is still not clear.

In most jawed fish, however, there are three general configurations.

Later, about 420 million years ago, the jawed fish evolved from one of the ostracoderms.

If it did, the scales would also be the oldest known traces of any jawed fish.

The popular name "spiny sharks" is really a misnomer for these early jawed fishes.

A significant evolutionary milestone during the Silurian was the appearance of jawed and bony fish.

Most workers have come to regard the agnatha as paraphyletic, having given rise to the jawed fishes.