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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 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 ...
Mosasauria is a clade of aquatic and semiaquatic squamates that lived during the Cretaceous period. Fossils belonging to the group have been found in all continents around the world.
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.
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.
They are oviparous, with clutch sizes averaging about 6 eggs per clutch. These lizards have a pectoral girdle, meaning that they must push their swallowed prey past it in order to eat. Despite this limitation, these lizards have been observed eating prey up to 33% of their body weight.
According to this hypothesis, features such as the transparent, fused eyelids and loss of external ears evolved to cope with fossorial difficulties, such as scratched corneas and dirt in the ears. [ 13 ] [ 15 ] Some primitive snakes are known to have possessed hindlimbs, but their pelvic bones lacked a direct connection to the vertebrae.
The hypothesis of Andreas Cellarius, showing the planetary motions in eccentric and epicyclical orbits. A hypothesis (pl.: hypotheses) is a proposed explanation for a phenomenon. A scientific hypothesis must be based on observations and make a testable and reproducible prediction about reality, in a process beginning with an educated guess or ...