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Re: dinosaur anatomy



<JSeward123> writes:

> I like Feduccia articles. By the way, I got a
> letter from Terry D. Jones of the Oregon State University Dept. of
Zoology who
> confirmed that Archaeopteryx was not tested for RTs. So the Discover mag.
> article didn't include Archaeopteryx.

Okay, which early birds were studied?
 
>   Basically, in my last e-mail I was just giving Ruben the benefit of the
> doubt. I'm really not certain about the metabolisms of Archaeopteryx and
other
> birds in question. But Dinosaurs do seem to muddy the metabolic waters.
They
> seem to have traits of both endothermy and ectothermy. Plus, if they were
> endotherms, how would they live without RTs?

Pelicans get by without them, I believe Gregory S. Paul has written that
kiwis get by without them (correct me if I'm wrong), and mouth-breathing
humans (as I have been for most of my life) don't use the RT's they've got!
 Sure, you could say that each of these examples is an exceptional case for
one reason or another, but they prove that it can be done.  Therefore,
endothermy without RT's is a fact.  In the case of we humans, you could say
that we can get away without using RT's because we can pursue sedentary
lifestyles, control our environment (by living in man-made dwellings),
dress up in warm clothes, drink as much as we like, and eat lots of food,
so loss of water vapor and heat through exhalation doesn't make much
difference most of the time.  Of course, this would be more problematical
to an Aborigine in the Australian outback, an Inuit in Alaska, or an
African living in the desert.  But we know that the world climate was
different in the Mesozoic than it is now, so this may explain how the
dinosaurs could thrive in a milder climate with a higher-than-reptilian
metabolism and no respiratory turbinates.
 
I don't have time to give a full report on this, but I think that you would
find articles in _The Complete Dinosaur_ most interesting.  In particular,
Chapter 32: _Dinosaurian Physiology: The Case for "Intermediate" Dinosaurs_
explains why the author, R. E. H. Reid, believes that dinosaurs had a
metabolism intermediate between that of reptiles and those of birds and
mammals, but closer to the latter two groups.  He points to many
hypothetical lines of evidence, including hemodynamics,   evidence for a
true four-chambered heart, growth rates, bone histology, erect posture,
mass homeothermy, pneumatic bones in the Saurischia, and the absence of an
insulating integument.

Of course, as we now know, there is evidence for insulation on the small
theropod, _Sinosauropteryx_, and I would think that the mass homeotherm
strategy would not be viable in the smaller forms of dinosaurs or in
dinosaur babies, which all started out quite small.  In Reid's view,
internal temperature regulation in dinosaurs as a group cannot be proven
unless it can be shown that all dinosaurs were either feathered or derived
from feathered ancestors.  (Your dice, Dinogeorge)! 

The author also brings up the point that there is a huge difference in the
standard metabolic rate of a shrew and a blue whale and, as John R. Horner
pointed out in _Dinosaur Lives_, there are living birds which routinely
drop their temperature by 20 to 30 degrees at night, in order to save
energy.  So there is quite a range to metabolisms even within extant
endothermic mammals and birds.

The chapter also suggests that bone histology reveals local growth rates,
and that different areas of  bone grow at different rates as an individual
develops asymmetrically, explaining why researchers have found both
fibro-lamellar and zonal bone on the same dinosaur specimen.  As an aside,
you may have noticed that John R. Horner will be presenting a talk on
metabolic implications of bone histology at Dinofest III in April.

You may also wish to look over the archives on these subjects; there has
already been a lot of discussion on RT's and metabolism.

Ralph Miller III <gbabcock@best.com>

(Holding up a marble): "Godzilla's brain is this size, while Kong is a
thinking animal."