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Re: Physiological Adaptations of the Dinosauria (long)






From: Waylon Rowley Subject: Re: Physiological Adaptations of the Dinosauria (long)

Hm. Possible, though improbable. But I think if *Sinosauropteryx* would
compress its...errr...protofeathers close to the body, this would still
allow quite little heat exchange. The "downy covering" was quite dense. >So I'd still say, if protofeathers aren't direct confirmation for >endothermy, they come very, very close.

I agree.

Oh! Seems like Ruben uses a different definition :-/ . Horner has >suggested that hadrosaurs used the mode you describe and has called this
"mesothermic". However, he thinks that only really big adult dinosaurs >were >gigantothermic.

Mesothermic could be misconstrued as being a metabolic condition between bradymetabolic ectotherms and tachymetabolic endotherms. But I like the word, so i'll use it....heheheh


On sauropod spines:

If they were sufficiently vascularized (which I don't know), yes. >Stegosaur plates were surely good for this purpose.

I would think a sauropod osteoderm/spine would be highly vascularized like one of the dorsal crocodilian scutes. I've also heard that stegosaur plates are highly vascularized....good example.



I do, based on the article I cited yesterday (or today, depending on >where you are...), which says that a heart that can sustain a sauropod >has alone a greater energy demand than a hypothetical ectotherm of >sauropod size.....

That is, assuming we know how a sauropod heart functioned, or if it had some adaptation like that of giraffe (carotid cuffs). For all we know, they had muscular contractions along their arteries that pushed the blood up (or some equally wild system).



This argument has been raised quite often, and the only counterargument >is that this has never happened elsewhere... Well, I think the >plesiomorphy for archosaurs or at least crurotarsans is the liver->pumped lung that Ruben imagines for dinosaurs (LOL) which allows >greater activity for ectotherms. I don't think one can explain the >success of big runners (some of them probably bipedal or semibipedal) >like ornithosuchids, rauisuchians (however paraphyletic they may be) >and early crocodilomorphs if they all were normally cold-blooded.
Indeed, crocs can gallop, and I've even read that if you manage to >scare a croc, it may run away on its hindlimbs!


(tries to imagine a T. rex liver pump....with no success)
About your comment on crocs: that's precisely the reason why I suspect we'll soon see Steve Irwin (a.k.a. "The Crocodile Hunter") in the obituary section soon.


On the isulating layer of Iridium in the atmosphere, you said:

Yes. At first it became terribly cold and dark for some months, and >later, when sunlight got through again, temperatures rose by 10 °C for >100 or 1000 years because the rock at the impact site (as well as the >global forest fires) gives lots of carbon dioxide when vaporized. Of >course, the scenario is more complicated, e. g. it involves terrible >acid rain...

I wonder how much stored heat in the ocean would rapidly transfer into the colder atmosphere after the impact....Maybe that killed off the marine reptiles? I don't see why global cooling would kill off the dinos, so they may have lived through that stage, but were later killed off by the heating.




Flying rather heats, because it is such a demanding exercise.
BTW, I've heard of 42 °C, and probably even more.

Flying *heats*....that's right. D'oh!

Lots of new books and papers show that this is a myth based on poor
statistics (the Signor-Lipps effect). Recently, someone found a
*Triceratops* skull 1.8 m below the K-T boundary, and hadrosaur >footprints have long been known from 37 _cm_ below the boundary, so the >3-m-gap is closed.

That's another thing I wanted to bring up. What role could the ceratopsion frill have played in cooling blood that was directed toward the gigantic narial fossae of these beasts? It seems like a good theropod crest analogue. And BTW, Mickey Mortimer has pointed out that some of the more basal ornithischia (and some more andvanced forms like stegosaurs) either reduced the size of their antorbital fossae or lack it entirely. I considered that when I was writing my article, and one possibility is convergent acquisition of endothermy or a reversal. I'm not a predentate lover, and I don't know too much about their nasal passages besides what i've seen in The Dinosauria (Weishampel et. al.), but I do think that if we going to look for RT's in any dino, it should be these guys....they may have found another way to recover moisture. And again, I apologize for the extra e-mail.
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