Re: Genetic Study Shows Snake Evolution

[Tony Canning <tonyc@foe.co.uk>]

Pluto77189@aol.com wrote:

> Look at all the legless lizards, and the lizards that are nearly legless--all 
> terrestrial.  Just like some dinosaurs were probably secondarily flightless, 
> some reptiles--maybe even some snakes--are secondarilary legless.
>
> If you mean they lost their limbs, re-evolved them and lost them again, well 
> that's certainly a novel suggestion...
>
> Good catch, I have been reading GSP's book, so "secondarily flightless" is on 
> my mind.  I meant that they might NOT be monophyletic, as in snakes might 
> have evolved leglessness many times, and possibly snakes are not all decended 
> from one, single ancestor.  the reasoning is that leglessness seems to be 
> pretty common in lizards, and in various forms.
>
> of course, I'm simply throwing out ideas, for all I know, genetic evidence 
> might just prove snakes al come from a single ancestor.

There is very strong evidence that snakes are monophyletic  - genetic, 
karyotypic, soft & hard anatomy.   But yes, limb reduction has happened many 
times in squamates independently.  Snakes were limbless by the early 
Cretaceous, whereas the legless skinks, anguids etc are more recent, and have 
not diversified to anything like the same extent.  It seems
likely that the specialised feeding & digestion of snakes is another reason why 
they are a much more diverse group than other limbless squamates.

Tony