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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. Temporal fenestrae in relation to the other skull openings in the dinosaur Massospondylus , a type of diapsid .
The lower temporal fenestra, usually present as a hole in the back of the skull of choristoderes, is closed by bone in Philydrosaurus. The eye sockets are large and spaced close together, similar to Monjurosuchus and Lazarussuchus .
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 ...
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 ...
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 tuatara and some extinct rhynchocephalians have a more rigid skull with a complete lower temporal bar closing the lower temporal fenestra formed by the fusion of the jugal and quadrate/quadratojugal bones, similar to the condition found in primitive diapsids. However early rhynchocephalians and lepidosauromorphs had an open lower temporal ...
The jugal lacks a "subtemporal extension" forming the bottom edge of the lower temporal fenestra, leaving the hole open from the bottom as if it was an arch. The squamosal also forms a large portion of the part of the skull behind the lower temporal fenestra, along with a thin and tall quadratojugal and a curved quadrate which probably ...
The jugal is three-pronged and has a distinctively elongated posteroventral process (rear lower prong). The posteroventral process may even be long enough to contact the sliver-shaped quadratojugal and enclose the lower edge of the lower temporal fenestra. Most sphenodonts have a fully enclosed lower temporal fenestra, but practically all ...