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This huge group of snakes contains almost 3,000 species (over 80% all extant snake species). Caenophidia is traditionally divided into two superfamilies, called Acrochordoidea (three species of Acrochordus filesnakes) and Colubroidea (all other colubroids), which are thought to have diverged about 60 million years ago. Some evidence suggests that the family Xenodermidae, traditionally treated as part of Colubroidea, might be more closely related to Acrochordoidea.
Caenophidia contains many familiar and obscure snakes. There is some uncertainty about the relationships of the major clades within Colubroidea, although recent work has clarified and refined traditional relationships based on tooth morphology (species with fixed fangs were placed into Elapidae, those with folding fangs into Viperidae, and those without fangs lumped into Colubridae).
Many (but not all) species of Caenophidia have venom, excellent color vision, spines on their hemipenes, and sophisticated chemosensory ability, prey acquisition ability, and antipredator tactics. Caenophidian snakes have lost all vestiges of their limbs and girdles. Other, less obvious, shared derived characteristics include the absence of coronoid bones in the skull and a vomer bone with several modifications associated with a well-developed vomeronasal organ.