Serpentes - snakes

The Serpentes, commonly known as snakes, are a familiar and well defined group, whose monophyly has strong support from a suite of both morphological and molecular characteristics (see below). Their position within the squamates, however, has proved extremely difficult to resolve. For more information regarding higher level squamate phylogeny, pleas refer to the Squamata main page.

Diversity and Lower Taxonomy:

Extant snakes are divided into two well-supported monophyletic sister groups: the Scolecophidia and the Alethinophidia.

Description:

Scolephidians are a poorly known group of snakes that are small, fossorial, and worm-like.

Alethinophidians, however, are the more familiar group, possessing what would generally be considered a snake-like body. They are generally larger and less fossorial.


Features:

• Limbless, but many retain traces of a pectoral girdle. Members of some of the more primitive families, such as the boas and pythons (contained within the superfamily Booidea), show external traces in the form of vestigial hindlimbs, called anal spurs, which flank the cloacal opening and are now only used for clasping during courtship.
• Well developed chemosensation, with forked tongue.
• Highly kinetic skull with eight points of rotation, allowing large prey to be swallowed whole. Each side of the skull can move independently.
• Many elements of the skull reduced or lost, facilitating the evolution of kinesis.
• The two sides of the mandible are loosely connected with cartilage at the rostral midline (in other jawed vertebrates, the two sides of the mandible are strongly fused to form the mandibular symphysis).
• Recurved teeth, preventing the escape of seized prey victims.
• No external ear openings.