Various ostracoderms of the class Osteostraci ('bony-shields') Cardipeltis bryanti, a lower Devonian ostracoderm from the Bighorn Mountains of Wyoming. Ventral (underside) exposed. Ostracoderms (lit. ' shell-skins ') are the armored jawless fish of the Paleozoic Era.The term does not often appear in classifications today because it …

Ostracoderms include both extinct groups, such as the heterostracans and osteostracans, and living. Ostracoderm, an archaic and informal term for a member of the group of armoured, jawless, fishlike vertebrates that emerged during the early part of the Paleozoic Era (542–251 million years ago). Ostracoderms include both extinct groups, such ...