Snakes are part of the group Toxicofera – associated with agamids, chamelions, ignuanian. Venom
evolved early on. So, there’s venom and there’s dangerous venom – not going to grab an iguana
and have serious venom problems.
But, in snakes, dangerous and nondangerous venoms. Milk Snakes have all the same genes that a
Taipan has, so why does the milk snake not exhibit those genes for venom?
Mimicry – why don’t snakes just become venomous instead of mimicking, if they have the same
genetic components? We don’t know.
Defining snakes: Reduction in characters
Reduced characters (shared in lizards)
Loss of limbs, but a whole bunch of other things have lost limbs skinks, dibamids, amphisbaenids,
Loss of girdles – no extant snakes have either girdle
Left lung reduced
Most have lost the automitc plane in vertebrae that allows tail to snap (but some have this still)
Scleral ossicles lost from eyeball – snakes move lens backwards and forwards, like a camera
Blood flow passes in front of retina, there is a hypothesis that they allow blood to move in front of
eyes when inactive because they don’t have eyelids, then draw blood back when awoken
Spectacle covering eye
Hyoid and skull elements missing
Most have 120 or more precloacal vertebrae
Do they originate from aquatic or burrowing ancestors?
Fossil evidence suggests burrowing, with limbs, terrestrial. But we could find an older aquatic fossil
next year, and it could change.
All fossils of ancient snakes from before meteor killed dinosaurs, they all came from Middle East
and one in Patagonia (which is really far away)
One theory that snakes lost limbs multiple times, some extant groups more closely related to one of