Re: Dinosaur Were Endotherms

[luisrey@ndirect.co.uk (luisrey)]

>    Snakes, *Draco*, some monitors, chameleons, and many other
>ectotherms did not change to a higher metabolism even when they are
>arboreal.

Well yes, but I agree that arboreal evolution doesn't create automatic or
compulsory high levels of activity or flying abilities. In fact evolution
doesn't have any specific compulsory 'plan' to make an arboreal animal
warm-blooded or cold-blooded. That we leave to contingency and adaptation.
Perhaps the proto-dinosaurs were already pre-adapted to higher levels of
activity thanks to their four chambered hearts and the thecodontian
semi-erect posture.
None of the cold-blooded animals mentioned above have the full erect
posture of a dinosaur or a bird.
After all, the main problem is becoming an animal fully capable of
generating its own heat. Of keeping temperature constant so it is capable
of sustained activity. This can be acomplished in many ways... so dinosaurs
were endotherms (no matter how 'intermediate' or 'unrefined' their
endothermy).

 At present, RTs are the best evidence that we have for the
>metabolism of dinosaurs, and the lack of them says that they are most
>likely ectotherms or quasi-ectotherms. Until they are found, the
>evidence suggests ectothermy.

I find the evidence inconclusive. Many dinosaurs had complex crests and
nasal passages that could have had turbinate structures. Also the fossil
preservation of many skulls won't allow us to see if there were turbinates
or not. Soft tissue is not preserved. On the other hand, do all birds and
do all endotherms have turbinates? I have heard commentaries contradicting
this.

And I am of the opinion that is becoming clear that most (or all) small
theropods were insulated with either protofeathers (like Sinosauropteryx)
of feathers (like Protarchaeoteryx).
It might be that the lack of feathers or other kinds of insulation in the
fossil record of theropods is the true 'artifact of preservation'.

Luis Rey

Visit my website on  http://www.ndirect.co.uk/~luisrey