Evolution
The cranial vault is composed of the endocranium forming the basal parts, topped by the skull roof in land vertebrates.
In fishes no distinct cranial vault as such exists, the skull being composed of loosely jointed bones. The cranial vault as a distinct unit arose with the fusion of the skull roof and the endocranium on the early Labyrinthodonts. In amphibians and reptiles the vault is rather small and inconspicuous, only forming proper vaults in mammals and birds.
Read more about this topic: Cranial Vault
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