Skull roof

Early armoured fish (such as jawless ostracoderms and jawed placoderms) did not have a skull in the common understanding of the word, but instead had a cartilaginous endocranium that was partially open from above.

The dermal bones gradually evolved into a fixed unit overlaying the endocranium like a heavy "lid", protecting the animal's head and brain from above.

A more or less full shield of fused dermal bones was common in early bony fishes of the Devonian, and particularly well developed in shallow water species.

In early sarcopterygians ("lobe-finned fish"), the skull roof was composed of numerous bony plates, particularly around the nostrils and behind each eye.

The skull roof in lungfish is composed of a number of bony plates that are not readily compared to those found in early amphibians.

[1] The earliest limbed tetrapods ("amphibians" in the broad sense) solidified a pattern of plates which formed the basis for that seen in all land-living vertebrates.

These early tetrapods (including temnospondyls, embolomeres, and various minor groups) have historically been termed "labyrinthodonts" ("maze teeth") or "stegocephalians" ("roof heads").

By extension, the "parietals" of fish are actually postparietals, while the tetrapod nasal and frontal bones develop from fused snout ossicles.

[19] Further tetrapodomorph discoveries, such as Acanthostega and Tiktaalik,[20] provide more concrete evidence for the anatomical shifts hypothesized by Westoll and Romer.

In two groups of early amniotes, the skull roof evolved temporal fenestrae to allow for greater movement of the jaw muscles.