Taxa such as Anapsida, Diapsida, Euryapsida, and Synapsida were named after their type of temporal fenestration.
Temporal fenestra are large holes in the side of the skull.
Many believe that they allow muscles to expand and to lengthen. An important distinction must be made between the type of fenestration found in certain taxa, and the taxa that were named after these types of fenestration. As such, it is primitive for amniotes because all their close relatives lack temporal fenestrae. Amniote skulls in lateral view showing the four main types of fenestration. Scale bars equal 1 cm.