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Insolation doesn't equal overheating
Topic Started: Apr 8 2009, 06:52 AM (287 Views)
Carlos
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This topic was inspired by a pm from GBA, which dealt with a theme very common in arguments from idiots with interest in dinosaurs that think that they know everything and yet they don't. It is often claimed that large dinosaurs (according to them, anything bigger than Deinonychus) didn't had any sort of insolation (feathers, fur, down, etc.) because they would suposedly over heat (the Mesozoic was tropical and all, although the late Cretaceous had a temperate climate and indeed Alaska was just as cold as today, judging by the availiable data). This stupid idea hypothesis was based on the fact large mammals like our beloved elephants and rhinos lack a large fur covering (and so do we), and because some dinosaurs also showed skin impressions of scales (I believe T. rex was among them, but AFAIK hadrosaurs and sauropods are the most important examples).

So far, I think the only dinosaurs that completly lacked down at all (even as babies) would had been sauropods (according to skin impressions of a baby titanosaur) and carnosaurs (remember Juravenator? It wasn't a coelurosaur at all, but a more basal tetanuran, and Darren Naish even linked it to allosaurs, suggesting it was a form that got small via neoteny); otherwise, species that had scaly skin as adults could theorically have downy babies. And I think its safe to say all small ornithicians and most small theropods (aside exceptions such as Juravenator), including pratically all coelurosaurs, were covered in a way or another, whereas as down, feathers or quills. And what about large dinosaurs?

To begin with, I think its quite obvious all maniraptors had feathers. Modern ratites like emus and ostriches have an absurdly large amount of long body feathers covering their bodies; one would expect they would overheat (their body cover can allow them to live in quite cold temperatures), but yet they live very comfortably in their natural habitat. This is because feathers are better insolators than fur; this doesn't mean they simply conserve body heat, but allow a more efficient control of the body temperature. Thus, they can actually also help an animal to decrease their body temperature, as when the feathers rise via muscular action air passes through taking away body heat more; they own structure of the feathers allows this to be quite efficient. Also note birds have a pulmonary air sack system, thus the air that enters the lungs passes through a complex system inside of the body that extends even to the bones, and takes body heat away as well. And, guess what, non-avian dinosaurs also had this system.

It is also worth to note that the tropical giant sloths of the past also had an absurdly dense pelt, thus suggesting that insolutary structures more primitive than feathers don't make an animal overheat. The only giant sloth with an appearent lack of fur would be the semi aquatic Thalassocnus, and even so I have doubts about that.

The clear fact that some dinosaurs lacked a covering of down or feathers (all very large, non-coelurosaur beasts [aside from the largest tyrannosaurs]) does shows that scaly dinosaurs did occured, but it may be likely that those were the exceptions, not the role. And indeed some very big dinosaurs, like ceratopsids, show a covering of fur like quills. So yeah.
Lemuria:
http://s1.zetaboards.com/Conceptual_Evolution/topic/5724950/

Terra Alternativa:
http://s1.zetaboards.com/Conceptual_Evolution/forum/460637/

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SIngemeister
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Whatever. My Dinosaur world will still have loads of scaly dinosaurs.
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