Ability to move in narrow spaces with clutter where limbs would just get in the way
Burrow more efficiently
New modes of locomotion
Distribute mass more widely and crawl on unstable substrates
Regional heterothermy – can stick a little bit of body out into sun. Female viviparous snakes are
known to just stick out part of body with embryos while keeping rest of body hidden
Long and elongate, basically tubes. So, very small food opening (mouth) relative to body size, so
somehow have to get enough food for a small opening
How do you deal?
Eat lots of small prey, like Scolecophidians
Eat really big pray (Alethinophidia)
How do you subdue and capture?
How do you eat them?
Large number of vertebrae in trunk (before cloaca)
Usually more than 120 vertebrae. For comparison, humans have 24. Some have as many as 400
Other limbless lizards can have as many as 200, but most are in the tail.
Skulls greatly reduced in number of bones – they’ve lost the arches, particularly upper temporal
arch, and result is that quadrate is just hanging by itself at back of skull. Quadrate very loosely
connected to rest of skull
In addition, bones on top of skull have grown done along side in very sturdy brain case.
Kinetic joints in skull
Maxilla bone loosely connected to rest of skull
Snakes broken into 2 clades at bottom of snake phylogeny Scolecophidia
Big brain case, defined lower jaw but not much upper jaw (Leptotyphlops)
Everything but blind snakes
Colubroids – basically everything but pythons and boas and basal alethinophidians
Pipe snake – Aniliidae. Stout, relatively inflexible skulls. Mostly burrowing, eat heavy but skinny
prey, same shape as snakes, like caecilians, amphisbaenians, eels, other snakes.
Evolution of constriction. They don’t really crush prey and break bones, whenever prey exhales
they tighten so it can’t breathe in.
So, evolution of constriction set stage for eating massive prey.
Large bulky prey characterizes most Alethinophidians, but not basal ones.
How to eat large body sizes?
Lengthen lower jaw and quadrate to allow for larger vertical gape
Mandibular liberation (no symphysis) – separate lower jaws
Streptostylic quadrate – movably suspended from skull – swings forward and backward
Jaw more kinetc – tooth bearing bones of upper jaw move separately, suspended on left and right
Snakes can tell head of prey from tail and orient themselves to eat head first so legs fold back
Boids can stretch mandibles a bit wider due to midway joint
Boas and pythons are world’s biggest snakes. Anaconda or Reticulated python? Both claimed to
get 10 m in length, but no good documentation in either. Largest were 9 m.
In terms of mass, largest living snake is anaconda – much heavier bodied snake than python.
Big prey consumption has developed in
Boas and pythons (may be two origins?)
Big vipers, which use venom. Most vipers do not constrict prey – they bite and let go so don’t risk
teeth falling out, then track them once dead.
Teeth Attached in modified pleurodont manner – (on inside of jaw bones, but have shallow socket
somewhat like thecodont)
Teeth found traditionally in maxilla, but also in roof of mouth on palatine and pterygoid, and
sometimes on premaxilla.
Aglyphous snakes: no enlarged fangs, often nonvenemous. Like python and boas.
Opisthoglyphous – colubrids: enlarged fangs at rear of maxilla. Venom. Sometimes have a groove
on teeth which is occasionally enclosed, and to get venom to prey, they chew on them a lot. Like
gila monsters. (except gila are on lower jaw)
Proteroglyphous: elapids (cobra, coral snake, etc) – immobile short front fangs, hollow, venom runs
down middle of tooth and injected in prey, generally neurotoxic venoms, squeezed via adductor