Osteostraci

thumb|right|The osteostracans reconstructed here belong to the major clade Cornuata, whose generalised morphology is exemplified by the [[zenaspidid Zenaspis (bottom left). Some highly derived head-shield morphologies are exemplified by the benneviaspidids Hoelaspis (top right) and Tauraspis (top left), or the thyestiid Tremataspis (bottom right). The latter has lost the paired fins, possibly as a consequence of an adaptation to burrowing habits.]] The class Osteostraci (meaning "bony shells") is an extinct taxon of bony-armored jawless fish, termed "ostracoderms", that lived in what is now No