Dermatocranium Fenestra and Classification

During the rise of the Amniotes over 330 million years ago, a shift in skull formation took place that is now being used to classify ancient organisms that used to roam the Earth. As a little background, the Amniotic family includes subfamilies like mammals, testudines (turtles), Lepidosauria (lizards, snakes, etc.) and the rest of the vertebral phylogeny. Each subsequent family is unique in that their dermatocranias each formed a fenestration, or hole. The location and number of holes in the skull allow us to classify the organisms into smaller groups. For example, an anapsid organism has no fenestrations in its skull. An organism, like a lepidosaur, would be a diapsid organism and have two fenestrations in its skull. The first of which is the dorsal fenestra located at the junction of the parietal, post orbital, and squamosal bones. The second is the lateral fenestra located at the junction of the jugal, quadratojugal, squamosal, and post orbital bones. Lastly, mammals are synapsid organisms meaning they only have one lateral fenestra in their dermatocranium.