Dunkleosteus prehistoric fish, artwork. This extinct fish lived in the late Devonian period (380-360 million years ago). Dunkleosteus was a large predatory fish that had plates of sharp bone within its jaws instead of teeth. It belonged to the class known as Placodermi, which were distinguished by having heavily-armoured heads and a scaleless body. Some species of Dunkleosteus are thought to have reached lengths approaching ten metres.