Postparietal

Postparietals are cranial bones present in fish and many tetrapods. Although initially a pair of bones, many lineages possess postparietals which were fused into a single bone. The postparietals were dermal bones situated along the midline of the skull, behind the parietal bones. They formed part of the rear edge of the skull roof, and the lateral edge of each postparietal often contacts the tabular and supratemporal bones. In fish, the postparietals are elongated, typically the largest components of the skull roof. Tetrapods possessed shorter postparietals, which were reduced further and shifted towards the braincase in amniotes.^[1] At several points in synapsid evolution, the postparietals fused to each other and the tabulars during embryological development. This fusion produces the interparietal bone, which is inherited by mammals.^[2] Postparietals are common in extinct amphibians and early reptiles. However, most living amphibians (of the group Lissamphibia) and living reptiles (of the group Sauria) lack postparietal bones, with a few exceptions.^[2]