Re: Dinosaur Were Endotherms

["Matthew Troutman" <m_troutman@hotmail.com>]

>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).

     High levels of activity can be linked to endothermy and GSPaul has 
shown convincing of high aerobic exercise capacity ( AEC ) in most 
dinosaurs. However, this is not evidence of mammalian or avian-type 
endothermy. If an animal does not have RTs it loses water that is 
necessary for high metabolic rates. Unless I see clear evidence of 
turbinates in dinosaurs I cannot support the endothermic hypothesis ( no 
matter how much I want it to be true ). 

Chameleons show a reasonably erect posture similiar to mammals and 
dinosaurs. 

I guess that some types of temperature regulation can make an animal 
loosely an endotherm when they still have some sorts of ectothermic 
features ( insulation, behavioral adaptations, etc ). 

>
>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.

    " Dinosaur skulls had features that _ could of _ or _ may of _ held 
turbinate-like structures " is not evidence of RTs or endothermy. Based 
on the evidence published so far, no dinosaurs had turbinates or could 
hold turbinates with their small nasal passages. Whether or not some 
birds have small anterior nasal passages may be something that can 
support that dinosaurs had turbinates, but until they are found, we have 
no evidence. The whole entire nasal passage was small according to 
figures in the Ruben et al. papers, though. 

Most endotherms have RTs except in derived exceptions ( such as in 
pelecans and whales ). The only endotherm that has no turbinates without 
reasonable explanation is the elephant ( though its nasal passage is 
rather big ).

>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'.

    I agree the evidence is pointing this way. Now whether insulation is 
indicative of endothermy is debateable because insulation can be of 
advantage to ectotherms with some endothermic characteristics ( activity 
rates, lung ventilation ) because it allows for some temperature 
stability.

Boy, have I set myself up for a flaming.


Matt Troutman

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