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The major reptile group Diapsida, for example, is defined by the presence of two temporal fenestrae on each side of the skull. The infratemporal fenestra, also called the lateral temporal fenestra or lower temporal fenestra, is the lower of the two and is exposed primarily in lateral (side) view.
This schematic shows the skull viewed from the left side. The middle opening is the orbit of the eye; the opening to the right of it is the temporal fenestra. Synapsids evolved a temporal fenestra behind each eye orbit on the lateral surface of the skull. It may have provided new attachment sites for jaw muscles.
The name Diapsida means "two arches", and diapsids are traditionally classified based on their two ancestral skull openings (temporal fenestrae) posteriorly above and below the eye. This arrangement allows for the attachment of larger, stronger jaw muscles , and enables the jaw to open more widely.
A euryapsid skull. Euryapsida is a polyphyletic (unnatural, as the various members are not closely related) group of sauropsids that are distinguished by a single temporal fenestra, an opening behind the orbit, under which the post-orbital and squamosal bones articulate.
An anapsid is an amniote whose skull lacks one or more skull openings (fenestra, or fossae) near the temples. [1] Traditionally, the Anapsida are considered the most primitive subclass of amniotes, the ancestral stock from which Synapsida and Diapsida evolved, making anapsids paraphyletic. It is, however, doubtful that all anapsids lack ...
Skull of the basal rhynchocephalian Planocephalosaurus, which has an open lower temporal fenestra. The complete lower temporal bar (caused by the fusion of the jugal and quadtrate/quadratojugal bones of the skull) of the tuatara, often historically asserted to be a primitive feature retained from earlier reptiles, is actually a derived feature ...
However, because more primitive rhynchocephalians have an open lower temporal fenestra with an incomplete temporal bar, this is thought to be derived characteristic of the tuatara and other members of the clade Sphenodontinae, rather than a primitive trait retained from early diapsids. The complete bar is thought to stabilise the skull during ...
The lower temporal fenestra is not fully enclosed in early archosauromorphs (and choristoderes) due to alterations to the structure of the quadratojugal bone at the rear lower corner of the skull. This bone is roughly L-shaped in these taxa, with a tall dorsal process (vertical branch), a short anterior process (forward branch), and a tiny or ...