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Temporal fenestrae are commonly (although not universally) seen in the fossilized skulls of dinosaurs and other sauropsids (the total group of reptiles, including birds). [1] The major reptile group Diapsida , for example, is defined by the presence of two temporal fenestrae on each side of the skull.
Testudines (Turtles, tortoises & terrapins) 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 .
Diagram of the diapsid skull with temporal openings, unlike in Anapsida. 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.
Unlike turtles, Pappochelys has teeth in its jaws and two pairs of holes in the back of the skull called temporal fenestrae. The presence of two pairs of fenestrae make the skull of Pappochelys diapsid, as opposed to the anapsid skulls of turtles that lack any temporal fenestrae. [1] [3]
It is now commonly believed that euryapsids (particularly sauropterygians) are in fact diapsids (which have two fenestrae behind the orbit) that lost the lower temporal fenestra. Euryapsids are usually considered entirely extinct, although turtles might be part of the sauropterygian clade [1] while other authors disagree. [2]
As a diapsid, Acerosodontosaurus had two holes known as temporal fenestrae on each side of the skull, behind the eyes. However, the lower temporal fenestra was not completely enclosed from below. In most early diapsids, such as Petrolacosaurus and Youngina , the lower edge of the lower temporal fenestra is formed by a bony bar composed of the ...
The turtle's skull is unique among living amniotes (which includes reptiles, birds and mammals); it is solid and rigid with no openings for muscle attachment (temporal fenestrae). [24] [25] Muscles instead attach to recesses in the back of the skull.
Many were classified as 'cotylosaurs' (a wastebasket taxon of stout-bodied 'primitive' reptiles or reptile-like tetrapods) or 'anapsids' (reptiles without temporal fenestrae, such as modern turtles). Parareptilia's usage was revived by cladistic studies, to refer to those traditional 'anapsids' that were thought to be unrelated to turtles.