| With their armored head shield and trunk shield composed of overlapping bony plates, the placoderms appear at first glance extremely similar to the ostracoderms. |
| These were jawless, armored fish informally called ostracoderms, but more correctly placed in the taxon Pteraspidomorphi. |
| Cartilaginous jaws would not fossilize, and the Ostracoderms may have possessed them. |
| Early fish from the fossil record are represented by a group of small, jawless, armored fish known as ostracoderms. |
| Enamel, or enameloid tissue covering tubercles, was clearly described in Ordovician vertebrates such as the ostracoderms. |
