The skeleton of the head may have originated in the earliest vertebrates. For the first time we discuss a theory that directly connects development and evolution. These elements, the conodonts themselves, may have been used in feeding.
Some ostracoderms have bony plates covering the head and upper trunk.
Others had a single massive protective shield. Like the odontodes we understand the armor plates to develop within the dermal layer of the skin. At least some of the earliest gnathostomes also possessed a fully armored head skeleton. Their skulls are very unlike those of other gnathostomes, such that assignments of homology are tentative at best. It seems very likely too, that, in the fashion the osteichthyans, they possessed skulls within their skulls.