- Main article: Triassic Divergence
Squamata is the group containing the lizards and snakes of our timeline. Due to competition from modern mammaliformes, lissamphibians, and sphenodonts (as well as several extinct groups), the lizards of Triassic Divergence are ancestrally arboreal. A few gliding and arboreal lineages are known, but the majority of their diversity is in the true flying lizards, the avesaurs.
Natural History Edit
Early squamates evolved from basal lepidosaurs at some point during the Triassic (as their Rhynchocephalian sister group is present during the Early Triassic), though fossils are not known in our timeline until the Early Juriassic. In our timeline, the lizards and snakes are found worldwide in a number of different groups. Most are insectivores.
During the Extended Triassic, the first arboreal squamates evolved and began to diversify. Terrestrial squamates were forced to marginal niches during most of the Mesozoic due to competition from other groups, but, ironically, these were the lineages to survive the Cretaceous-Paleogene Extinction in North America and Africa. They diversified in arboreal and volant niches extremely rapidly after the extinction, with true flying forms known from the Paleocene. The African lineage became extinct, but the ancestrally North American lineage has representatives across the world in both flying and fully arboreal forms. Gliding forms are much less common but still represented.
The relationships among the living squamates are fairly well-resolved based on increasing adaptation to life in trees and then flight. The most basal group is the Scansorosauria, which appear to be the most similar to the secondarily-terrestrial common ancestor of all living squamates. The sister group to the squamates with flying adaptations (Avesauromorpha) is the Bratosauria, characterized by specialized ankle morphology for a fully-arboreal lifestyle. Volasauria, sister group to the Avesauriformes, is characterized by gliding membranes on expanded ribs and forelimbs. Finally, the Avesauriformes are characterized by wing membranes in a morphology not similar to any flying animals known in our timeline. The avesauriformes are then represented by two clades: the Insectisauria and the Avesauria proper.
Scansorosaurs are small, morphologically conservative squamates similar to the skinks of our timeline. As is the case for the Triassic Divergence lizards, their history shows several switches between arboreality and terrestriality. Today, they occupy a niche somewhere in the middle of the two, lacking specialized ankle morphology for tree-dwelling but still seeking refuge in vegetation when confronted with danger. They are entirely insectivorous.
Scansorosaurs can be found only in the lower latitudes of North America, most common in the deserts and scrublands of our Southwestern United States and Mexico.
Scansorosaurus - The most common genus in its group, it is primarily a desert-dwelling lizard that feeds on insects in arid to semi-arid areas.
Bratosaurs are typically small to midsize squamates that tend to spend their entire lives in trees. They are typically insectivorous or herbivorous in some form, and they are rather adaptable when compared with the scansorosaurs. They have a specialized ankle morphology that allows them to be superb climbers.
Bratosaurs are the most wide-ranging squamates (other than the avesauriformes), with representatives on every continent except Australia (excluding New Guinea) and Antarctica. Though they seem to have evolved in North America, the greatest species diversity is in Southeast Asia. Interestingly, they are rare in the jungles of central Africa, and they are entirely absent in the majority of South America, despite their seeming suitability for these environments.