Dermal bone appears first in vertebrate evolution, either as a head shield or in some cases, an entire armor-like exoskeleton, [A]. In the derived vertebrates seen today, for example humans, this head shield has been reduced to a few paired, skin covered plates overlying the brain as well as some parts of the jaw.

This picture shows the beginnings of bone differentiation in the head from above (top), and a close up of the developing parietal (bottom left) and frontal lobes (bottom right). Already the paired midline structures are obvious.