Reptilia  

The earliest diapsids (and indeed, all known stem diapsids) lacked a tympanum and could not hear high-frequency air-borne sounds, as shown by the lack of a quadrate emargination (the structure that supports the tympanum in most extant diapsids) and the robust shape of their stapes. This indicates that the tympanum present in most saurians developed independently from the tympanum of turtles and mammals (except if turtles are saurians, as recently suggested by Rieppel and deBraga (1996).

A few saurians have lost their tympanum and their ability to hear high-frequency air-borne sounds. These include snakes and many other lepidosaurs, such as Sphenodon, amphisbaenids, Tympanocryptis, Aphaniotes (Barry, 1963). These saurians can only hear low-frequency seismic vibrations (sounds transmitted through the ground).

Early phylogenies of diapsids suggested that the tympanum and the ability to hear high-frequency air-borne sounds had appeared separately in lepidosauromorphs and in archosauromorphs because younginiforms, formerly believed to be the oldest known lepidosauromorphs, apparently lacked a tympanum (Benton, 1985; Evans, 1988). However, the reinterpretation of younginiforms as stem diapsids implies that the tympanum appeared only once in diapsids, probably soon before the divergence between lepidosauromorphs and archosauromorphs (Laurin, 1991).

Only skeletal autapomorphies (unique derived characters) can be confidently assigned to Diapsida because all the basal lineages of diapsids are extinct. In addition to the presence of an upper and a lower lateral temporal fenestra, these include:

• A suborbital fenestra (Fig. 2). This is a relatively large hole in the palate that is located between the palatine, the ectopterygoid, and the maxilla. Other taxa may have a foramen (a small hole just large enough to allow passage for a nerve or a blood vessel) in this region, but there is usually no fenestra.
• A long radius, measuring between 70% and 90% of the length of the humerus. This ratio is variable in extant diapsids, but early diapsids consistently had a longer radius than other taxa, in which it was typically less than 70% of the humeral length.

Figure 2. Diapsid skulls in palatal view. A, Petrolacosaurus, a Pennsylvanian araeoscelidian; B, Claudiosaurus, an Upper Permian neodiapsid; C, Youngina, an Upper Permian younginiform; D, Clevosaurus, a Late Triassic sphenodontid (a saurian).
Redrawn from A, Reisz, 1981; B and C, Carroll, 1981; D, Fraser, 1988. Scale bar equals 1 cm. Copyright © 2000 Michel Laurin.

Skeletal autapomorphies can unambiguously be attributed to Sauria, and other characters (soft anatomical, physiological, etc.) present in saurians but not in other extant amniotes are also usually attributed to Sauria, although they may have been present in other diapsids and even in their close relatives ("Protorothyridids" and captorhinids). Saurian autapomorphies include:

• A low concentration of urea in the blood plasma resulting from a loss or suppression of the urea cycle. Lissamphibians, mammals, and turtles have a higher concentration of urea in their plasma.
• The loss of the apposition between the kidney and the adrenal gland. These two organs are juxtaposed in lissamphibians, mammals, and turtles.
• The presence of Huxley's foramen. This foramen is a hole in the distal end of the extracolumella (a cartilaginous extension of the stapes that contacts the tympanum). Huxley's foramen is absent in lissamphibians, mammals, and turtles.
• Temporal muscles originating on the dorsolateral surface of the skull table. In araeoscelidians and younginiforms, the temporal muscles originate from a fascia attached to the lateral edge of the skull table and from the ventral surface of the skull table.
• Prefrontal-nasal suture anterolaterally oriented (Fig. 3D). This suture is parasagittal in araeoscelidians, Claudiosaurus, and younginiforms (Fig. 3A-C).
• Squamosal confined to the dorsal half of the skull, except for a narrow ventral process supporting the quadrate. The squamosal of younginiforms, Apsisaurus, and araeoscelidians is broad ventrally.
• Strong, broad contact between the paroccipital process and the cheek. This contact is weak and often cartilaginous in younginiforms and araeoscelidians.
• Quadrate deeply emarginated posteriorly. The quadrate of saurians supports a tympanum in its deep posterior emargination. The quadrate of younginiforms has a very shallow emargination that probably did not support a tympanum. The quadrate of Apsisaurus and araeoscelidians is not emarginated.
• Slender stapes. The stapes of saurians is modified to function as a middle ear ossicle to transmit high-frequency air-borne sounds from the tympanum to the inner ear. The stapes of younginiforms and araeoscelidians is more massive and it is not specialized as a middle ear ossicle.
• Dorsal process of stapes with ossified connection to paroccipital process of opisthotic. In other taxa, this connection is cartilaginous (or it may consist of a tendon), when it is present.
• Large retroarticular process. This is the insertion point for the muscles that open the lower jaw. The retroarticular process of araeoscelidians, Coelurosauravus, and younginiforms is much smaller.
• Cleithrum absent. The cleithrum is a dermal bone located on the anterior edge of the scapula, dorsal to the clavicle. It is present in araeoscelidians, Coelurosauravus, and younginiforms.
• Lateral manual centrale (a bone in the wrist) small or absent. The lateral and medial centralia are approximately of equal size in araeoscelidians and in some younginiforms primitively (in Acerosodontosaurus).
• Fifth distal tarsal absent (this is a small bone in the ankle, proximal to the fifth toe). Araeoscelidians, Coelurosauravus, and youngina have five distal tarsals.
• Fifth metatarsal hooked (this bone supports the fifth toe). This bone is straight in other diapsids.

Figure 3. Diapsid skulls in dorsal view. A, Petrolacosaurus, a Pennsylvanian araeoscelidian; B, Claudiosaurus, an Upper Permian neodiapsid; C, Youngina, an Upper Permian younginiform; D, Clevosaurus, a Late Triassic sphenodontid (a saurian).
Redrawn from A, Reisz, 1981; B and C, Carroll, 1981; D, Fraser, 1988. Scale bar equals 1 cm. Copyright © 2000 Michel Laurin.

The linked page Autapomorphies of diapsid clades provides a list of autapomorphies of Neodiapsida and other clades smaller than Diapsida but more inclusive than Sauria.

Animal / dung saprobe
Basidiobolus ranarum is saprobic in/on dung or excretions of dung of Reptilia

Reptilia preys on:
Arthropoda
Gallicolumba luzonica
Meriones crassus
Sorex araneus

Based on studies in:
USA: California, Coachella Valley (Desert or dune)

This list may not be complete but is based on published studies.