Serpentes (Snakes)

Abstract Snakes are a diverse group of long‐bodied, limb‐reduced reptiles closely related to lizards; together they are termed squamate reptiles. Primitive snakes with vestigial legs appear in the fossil record of the Cretaceous period (∼90 Mya). Snakes have since been diversified rapidly, and now comprise ∼3500 species that occupy terrestrial, subterranean, aboreal and aquatic niches. All snakes are predators, having highly mobile skulls and jaws that can often swallow prey much larger than their own diameter. Primitive snakes such as boas, pythons and blindsnakes lack venom fangs. Such fangs have evolved repeatedly within more advanced snakes, called the Colubroidea, which make up ∼80% of the diversity of living snakes: front fangs in viperids (e.g. vipers and rattlesnakes), fixed front fangs in elapids (e.g. mambas and cobras) and rear fangs in many lineages of colubrids (e.g. boomslangs and twig snakes). Key Concepts: Snakes are just one of the many lineages of limb‐reduced lizards – though by far the most successful ones. Snakes have highly flexible (kinetic) skulls and lower jaws, and many forms can engulf prey wider than their heads. Snakes are one of the most rapidly diversifying groups, with more than 3000 living species, mostly belonging to the Colubroidea. Venom‐delivery systems (fangs and glands) have evolved multiple times within the most advanced snake lineage (Colubroidea). The fossil snakes Najash and Pachyrhachis (∼90 My old) retain prominent external hindlimbs, as would be expected given that snakes evolved from lizard‐like reptiles.