[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

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 trap it.


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
sails.

All from equatorial regions (which is actually irrelevant to your >argument.

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?
_________________________________________________________________
Get your FREE download of MSN Explorer at http://explorer.msn.com