Sauria is the clade of diapsids containing the most recent common ancestor of Archosauria (which includes crocodilians and birds) and Lepidosauria (which includes squamates and the tuatara), and all its descendants. Since most molecular phylogenies recover turtles as more closely related to archosaurs than to lepidosaurs as part of Archelosauria, Sauria can be considered the crown group of diapsids, or reptiles in general. Depending on the systematics, Sauria includes all modern reptiles or most of them (including birds, a type of archosaur) as well as various extinct groups.
Sauria lies within the larger total group Sauropsida, which also contains various stem-reptiles which are more closely related to reptiles than to mammals. The redefinition to cover the last common ancestor of archosaurs and lepidosaurs was the result of papers by Jacques Gauthier and colleagues in the 1980s.
Genomic studies and comprehensive studies in the fossil record suggest that turtles are closely related to archosaurs as part of Sauria, and not to the non-saurian parareptiles as previously thought.
Synapomorphies
The synapomorphies or characters that unite the clade Sauria also help them be distinguished from stem-saurians in Diapsida or stem-reptiles in clade Sauropsida in the following categories based on the following regions of the body.
- Cephalad region
- Dorsal origin of temporal musculature
- Loss of caniniform region in maxillary tooth row
- External nares close to the midline
- Postparietal absent
- Squamosal mainly restricted to top of skull
- The occipital flange of the squamosal is little exposed on the occiput
- Anterior process of squamosal narrow
- Quadrate exposed laterally
- Unossified dorsal process of stapes
- Stapes slender
- Trunk region
- Sacral ribs oriented laterally
- Ontogenetic fusion of caudal ribs
- Trunk ribs mostly single headed
- Pectoral region
- Cleithrum absent
- Pelvic region
- Modified ilium
- Limb region
- Tubular bone lost
- Entepicondylar foramen absent
- Radius as long as ulna
- Small proximal carpals and tarsal
- Fifth distal tarsal absent
- Short and stout fifth or hooked metatarsal
- Perforating foramen of manus lost
However, some of these characters might be lost or modified in several lineages, particularly among birds and turtles; it is best to see these characters as the ancestral features that were present in the ancestral saurian.
The cladogram below follows the analysis of Li et al. (2018). It places turtles within Diapsida but outside of Sauria (the Lepidosauromorpha + Archosauromorpha clade).Cladogram of Jenkins et al. 2026, which found Pantestudines within Archosauromorpha with strong morphological support.