Please forward this error screen to sharedip-192186206129. This article is about the animal. Snakes are elongated, books on snakes of the world pdf, carnivorous reptiles of the suborder Serpentes.
Ireland, Iceland, Greenland, the Hawaiian archipelago, and the islands of New Zealand, and many small islands of the Atlantic and central Pacific oceans. Most species are nonvenomous and those that have venom use it primarily to kill and subdue prey rather than for self-defense. Some possess venom potent enough to cause painful injury or death to humans. Nonvenomous snakes either swallow prey alive or kill by constriction. Note: the tree only indicates relationships, not evolutionary branching times. The fossil record of snakes is relatively poor because snake skeletons are typically small and fragile making fossilization uncommon.
Based on comparative anatomy, there is consensus that snakes descended from lizards. Pythons and boas—primitive groups among modern snakes—have vestigial hind limbs: tiny, clawed digits known as anal spurs, which are used to grasp during mating. The families Leptotyphlopidae and Typhlopidae also possess remnants of the pelvic girdle, appearing as horny projections when visible. Front limbs are nonexistent in all known snakes. This is caused by the evolution of their Hox genes, controlling limb morphogenesis. The expansion of grasslands in North America also led to an explosive radiation among snakes. This hypothesis was strengthened in 2015 by the discovery of a 113m year-old fossil of a four-legged snake in Brazil that has been named Tetrapodophis amplectus.
It has many snake-like features, is adapted for burrowing and its stomach indicates that it was preying on other animals. An alternative hypothesis, based on morphology, suggests the ancestors of snakes were related to mosasaurs—extinct aquatic reptiles from the Cretaceous—which in turn are thought to have derived from varanid lizards. Genetic studies in recent years have indicated snakes are not as closely related to monitor lizards as was once believed—and therefore not to mosasaurs, the proposed ancestor in the aquatic scenario of their evolution. However, more evidence links mosasaurs to snakes than to varanids. Fragmented remains found from the Jurassic and Early Cretaceous indicate deeper fossil records for these groups, which may potentially refute either hypothesis. More advanced snakes have no remnants of limbs, but basal snakes such as pythons and boas do have traces of highly reduced, vestigial hind limbs.