Alethinophidia
The Alethinophidia are an infraorder of snakes that includes all snakes other than blind snakes and thread snakes. Snakes have long been grouped into families within Alethinophidia based on their morphology, especially that of their teeth. More modern phylogenetic hypotheses using genetic data support the recognition of 19 extant families (see below), although the taxonomy of alethinophidian snakes has long been debated, and ultimately the decision whether to assign a particular clade to a particular Linnaean rank (such as a superfamily, family, or subfamily) is arbitrary. Etymology. The infraorder name Alethinophidia derives from the two Ancient Greek words (), meaning  truthful, genuine, and (), meaning "snake". Fossil record. Fossils of alethinophidians were found in Cenomanian (Middle Cretaceous) sites of Wadi Milk Formation in Wadi Abu Hashim, Sudan. "Coniophis" presents the vertebral morphology similar to modern-day Aniliidae. Two extinct families from the same location, the Anomalophiidae and Russellophiidae, also belong to the Alethinophidia. "Krebsophis" is the earliest russellophiid. The family Nigerophiidae includes both aquatic "Nubianophis" from Wadi Abu Hashim and "Nigerophis" from the Palaeocene of Niger. The genus "Eoanilius" (belongs to Aniliidae) appeared in the Eocene. It is also existed in Oligocene and early Miocene.