Re: Evolution:Small Scale/Grand Scale

[tonyc@foe.co.uk (Tony Canning)]

Amado Narvaez wrote:

> Do I recall correctly that some paleontologists think that saurischians 
> were more likely to be warm-blooded than ornithischians were? If that's 
> the case (saurischians=warm-blooded; ornithischians=cold-blooded), why 
> should these two dramatically different orders be lumped together at all? I 
> would think that the attribute of warm-bloodedness is almost as great a 
> milestone in the history of evolution as giving birth to live young.
or vertebrates."

Well yes, but live-bearing has appeared many times in insects, arachnids,
fish, amphibians reptiles (modern) etc. etc. - we can't reclassify anything
on that basis.  Endothermy similarly seems to evolve relatively easily if
natural selection favours it.  Neither of these factors is relevant to 
systematics.

Suppose we discovered that small therapods were endothermic and large
therapods were ectothermic.  Their geneological relationships would remain
the same as before this discovery - they would still all be therapods.  We
would merely have to say that therapod physiology was variable.

Tony Canning
tonyc@foe.co.uk