Adaptive explanations for the temporal fenestration in reptiles are briefly reviewed. With few possible exceptions, fenestrate appeared first in the reptiles, and have seemingly evolved independently in several different phyletic lines.
The several explanations for fenestration offered by previous authors include speculations that open spaces in the skull permitted bulging of the jaw-closing muscles, and that fenestrae formed in areas of reduced stress where the presence of bone would be functionally useless. The first of these does not readily apply to initial evolutionary stages; the second is more satisfactory.
Certain features of muscular attachments to bones are dealt with, and their implications applied to the fenestration problem to add another possible explanation (which need not contradict previously published suggestions).
Considerations of cranial strength in tetrapod skulls led to speculations on the lack of fenestration in temnospondyls, anthracosaurs, microsaurs and cotylosaurs.
Emargination of the skull roof in turtles is also discussed.