Frontoparietala

The frontoparietal, or frontoparietal bone, is a cranial element found in the skull roofs of various vertebrates. It is a midline bone that contributes to the upper part of the braincase and the dorsal skull surface.

In many amniotes, the frontoparietal is formed by the fusion of the frontal and parietal regions during development, producing a single midline element. In other lineages, particularly some early tetrapods, fishes, and certain reptiles, a distinct frontoparietal bone can remain as an independent structure. The presence or absence of a separate frontoparietal—and whether it is a fused or separate element—varies across taxa.

Anatomically, the frontoparietal is positioned on the top of the skull, adjacent to bones such as the frontal, parietal (or its successor elements), and surrounding marginal bones. Its exact articulations and boundaries depend on the group and the degree of fusion within the skull roof. In taxa where it exists as a separate bone, the frontoparietal helps shape the cranial vault and provides surface area for muscle attachment and protection of brain tissue.

Developmentally, frontoparietal formation generally occurs through intramembranous ossification, with its composition arising from regional skull bone primordia that may fuse over ontogeny. Evolutionarily, the frontoparietal reflects broader patterns of skull roof remodeling, including midline fusion and regional differentiation of the frontal and parietal bones.

In mammals, a distinct frontoparietal bone is typically not present as a separate element; the frontal and parietal bones remain separate, and the skull roof is organized around those primary bones. See also frontal bone, parietal bone, interparietal bone.