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It is thought that this was the result of descent from a common venom-producing squamate ancestor; the hypothesis was described simply as the "venom clade" when first proposed to the scientific community. [2] The venom clade included Anguidae for phylogenetic reasons and adopted a previously suggested clade name: Toxicofera. [14]
The single origin hypothesis also suggests that venom systems subsequently atrophied, or were completely lost, independently in a number of lineages. [20] The phylogenetic position of Iguania within Toxicofera is supported by most molecular studies, but not by morphological ones. [30] The "Toxicoferan hypothesis" was subsequently challenged.
The Toxicofera hypothesis further implies [according to whom?] that "nonvenomous" snake lineages have either lost the ability to produce venom (but may still have lingering venom pseudogenes), or actually do produce venom in small quantities, likely sufficient [according to whom?] to help capture small prey but causing no harm to humans when ...
Several other predators of the pit viper (mongooses and hedgehogs) show the same type of relationship between snakes, which helps to support the hypothesis that venom has a very strong defensive role along with a trophic role. Which in turn supports the idea that predation on the snakes can be the arms race that produces snake venom evolution. [31]
Toxicofera contains about 4,600 species, (nearly 60%) of extant Squamata. It encompasses all venomous reptile species , as well as numerous related non-venomous species. There is little morphological evidence to support this grouping; however, it has been recovered by all molecular analyses as of 2012.
Toxicofera is part of WikiProject Amphibians and Reptiles, an effort to make Wikipedia a standardized, ... This is fine as a stand-alone theory or hypothesis, but the ...
However, there is debate among many academics about venom metering in snakes. The alternative to venom metering is the pressure balance hypothesis. [citation needed] The pressure balance hypothesis cites the retraction of the fang sheath as the many mechanism for producing outward venom flow from the venom delivery system.
The oldest widely accepted member of Anguimorpha is Dorsetisaurus from the Late Jurassic of Europe and North America. [2] In 2022, the genus Cryptovaranoides was described from the latest Triassic of England.