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Re: Bird reduce their "heating bills" in cold climates



Jura <pristichampsus@yahoo.com> wrote:


> Hardly anything about the skeleton of green iguanas,
> screams arboreal either. 


This is true.  And, as commonly noted, even goats can climb trees.


However... if one were to hypothesize that a particular fossil taxon was 
habitually arboreal, then this hypothesis will stand or fall based on its 
arboreal-related characters.  So far, no ornithopod (including _Leallynasaura_) 
shows any adaptations for climbing or perching.  


This is not to suggest that ornithopods (especially the smaller ones) *never* 
climbed trees.  But, if climbing or perching was indeed an integral part of the 
behavior of an ornithopod (as once suggested for _Hypsilophodon_) we would 
expect to see limb proportions or discrete characters associated with 
arboreality (including scaling trunks or grasping branches).  We don't - not in 
_Hypsilophodon_, or any other known ornithopod (or ornithischian in general).


This issue comes up in the origin-of-avian-flight debate.  Those who argue for 
an exclusively "trees-down" origin for avian flight argue that _Archaeopteryx_ 
was highly adapted for an arboreal lifestyle.  However, the anatomical evidence 
simply doesn't support this interpretation.  _Archaeopteryx_'s climbing and 
perching abilities were rudimentary, at best.




Cheers

Tim