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Re: Physiological Adaptations of the Dinosauria (long)
To David Marjanovic, who wrote:
To shortly summarize the discussions -- Nonsense. Crocodiles,
prolacertiforms etc. don't have respiratory turbinates "either".
I was merely referring to what Ruben had said in a press release.
Oh sure this is direct confirmation. Ectotherms aren't insulated because
they can only regulate their body temperature by exchanging warmth with
their surroundings, which any insulation would impede.
Well, I wouldn't go far as to say that insulations completely impedes
thermoregulation in an ectotherm. A hypothetical cold-blooded
Sinosauropteryx could compress its...errr..."filaments" close to the body,
allowing greater heat transfer with the environment, then fluff itself up to
Erm... why? Why not simply endothermic? Today, heterothermy, if I have
correctly understood it, is an adaptation of very small endotherms (bats,
hummingbirds) for saving energy at times when they can't eat (when they
sleep). Probably hibernation is also called heterothermy.
I've heard the term "heterothermy" used in the context of sauropods, where
young would be endothermic and progressively become gigantothermic as they
grew into adulthood.
For gigantothermy, one needs either a very compact body shape and AFAIK
>lots of fat (the way of the leatherback turtle, the only known
>gigantotherm) or, considering dinosaur proportions, great size, maybe
>starting at elephant size or above. Look at sauropods, the dinosaurs
>that should be the most likely gigantotherms: They have long necks and
>tails, air sacs en masse (kind of contradiction...) and relatively
>longer legs than elephants. These are interpreted as adaptations for
>surface enlargement and thus cooling. Gigantotherms should be expected
>to have opposite adaptations to stay cool by bulk.
Forgive my rampant speculation, but maybe the iguana-like spines on
sauropods also allowed cooling? I'm not saying that sauropods were
endothermic throughout their entire lives, but younger individuals could
have benefitted from a higher metabolism.
This fits the observation (forgot the ref now, probably Currie's and
Padian's _Encyclopedia of Dinosaurs_) that in theropods (except birds)
>there was a trend to enlarge the antorbital fenestra, whereas in ?all
>other archosaurs there was a trend to reduce its size.
Maybe archosaurs are plesiomorphically endothermic, with crocodilians
reversing the condition, but I'm sure there's a good reason why I'm probably
wrong about that....
Why do you mention *"Dilophosaurus" sinensis*?
Because (to my knowledge) ?D. sinensis has the largest nasolacrimal crest
among coelophysoids (with the possible exception of D. wetherilli)
which when acting as a radiator panel for the superior nasal artery, would
give it a higher condensation rate than, say, a similarly-sized E. baldwini.
If you took a measurement of the istopic ratio for the crest itself and the
base of the antorbital fossa, it should indicate how much heat was being
lost, and whether condensation was really possible in this animal.
Well, there were several temperature fluctuations in the Mesozoic; in >the
Maastrichtian (not at its end) average temperatures rose by 3 °C (forgot
the ref :-( ), what seemingly didn't affect dinosaurs, and then >the
meteorite came. Mantra time: Could a rise in temperature (or its >cause, or
its effects, or whatever) explain THE WHOLE K-T extinction?
Ok, i'm wrong about the gradual increase. How about the meteor itself
though? Could a thin iridium/ash/vaporized rock cloud act as an insulation
to cover the earth and turn it into a (temporary) toaster-oven?
While reptiles are (and birds can at least withstand higher air
>temperatures because their body temperatures are tremendous), mammals
>get into real trouble when their surroundings are warmer than them. (I'm
not talking of sauna conditions, where e. g. you can't lose water >and the
time is limited.)
What about the small subterranian mammals? They could simply hole-up in
their little dens until the crisis ended- like a kangaroo rat.
As for reptiles, you said:
For a short time. Then they'd desperately look for a cool place.
Reptiles also have the ability to burrow, or in the case of crocodilians to
submerge themselves in cool water.
And on bird RT's:
Hm. They would probably, but they have no cooling effect...
Well, the birds would've pulled through nicely because, as you said, they
have much higher body temperatures (the highest i've heard of reached 40º
C), and the fact that they could cool themselves by flying.
Many dinosaurs from the southern hemisphere (e.g. Amargasaurus
cazui, Spinosaurus aegyptiacus, Ouranosaurus nigeriensis) have dorsal
All from equatorial regions (which is actually irrelevant to your
The point is that these animals boosted their body temperature with the
sails *beyond* (for food energy conservation) that of their normal metabolic
rate to facilitate condensation.
Question -- Did *Spinosaurus* live in the southern hemisphere? Today,
>North Africa is around 30° north...
From the paleomaps i've seen, S. America and N. Africa are close to the
equator. Besides, we may be wildly off when it comes to the continents exact
position, as is hinted at by gondwanan fauna.
AFAIK, there was no significant increase in temperature, and the K-T
extinction was (mantra) NOT gradual!
I think that remains to be seen. And as for the more gradual decline of
dinosaurs during the LK, hmmmmm....I thought that was a given.
And let's not forget the Carcharodontosaurids and Abelisaurs....their *HUGE*
(e.g. 30%+ total skull length) antorbital fenestrae would be perfect for the
hotter equatorial regions they lived in. Increased fossa area = increased
condensation. BTW, sorry for the extra e-mail I sent you, i'm still adapting
to the list.....can you tell me what "AFAIK" means?
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