Cephalaspis is the genus name for four different species of ancient fish. They, along with dozens of other species, belonged to the Osteostraci class (making them Ostracoderms). All Ostracoderms had bony armor, but lacked jaws. They all went extinct at the end of the Devonian, around 360 million years ago.
Cephalaspis in particular only lasted till the early Devonian, around 400 million years ago, and all fossils have been found in what is now Western Europe. They ranged in size from a few inches, to about a foot. These fish were most likely fresh water bottom feeders, since their mouths were located on the bottom side of the head. They may have moved their large heads from side to side, stirring up debris and locating smaller animals to feed on.
Status : Extinct for 400 million years
Location : Western Europe
Size : Length up to 1ft (30cm)
Classification : Phylum : Chordata -- Class : Osteostraci -- Genus : Cephalaspis