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Re: [Fw: Physiological Adaptations of the Dinosauria (long)]
"David Marjanovic" <David.Marjanovic@gmx.at> wrote:
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.
I don't see why not. I think that we tend to underestimate the
physiological capabilities of extant reptiles just because they are
"cold-blooded." Yet, even without a tachymetabolism, reptiles are capable
of some very mammal-like things.
One of my favourite examples is that of _Palmatogecko rangei_ which lives
in the coastal Namib Desert and hunts its prey at night when Atlantic
winds chill the place to 4 degrees C. Yet in such harse extremes these
little buggers are actively moving about (not only that, but they only
come out when it gets cool). They are hardly gigantothermic either since
they max out at 4 inches and have translucent skin. If any animal was ever
deserving of a physiological study, it's these guys.
As for sustained running, if one were to explain active crocodylimorphs
through "warm-bloodedness" then one would be hard pressed to explain how
"cold-blooded" varanids can sustained active runs (or at least jogs). They
do it with only a three chambered (5 real chambered, but only three
completely separate ones) heart and no diaphragm. But they do make up for
it with the only alveolar lung system found in extant reptiles.
Energetic, aerobic, warm-blood, but not "warm-blooded."
As such, I have no trouble with bradymetabolic dinosaurs. IMHO everything
mentioned about dinosaur metabolism in Heresies, all seems plausible with
a "typical" reptilian physiology.
In all honesty, I'm still trying to figure out why true bradymetabolic,
leaky RBC endothermy would evolve at all.
> Indeed, crocs can gallop, and I've even read that if you manage to scare
>a croc, it may run away on its hindlimbs!
Well the bipedal part is a new one on me. I think I've heard about this in
hatchlings and juveniles, but only bits and pieces.
As for galloping; for all those interested one can view a galloping
_Crocodylus johnstoni_ at crocodilian.com
I believe someone on the list once mentioned how croc gallops were
analogous to a squirrel gallop, but, to me, it looks more like a cat's
gallop than that of a squirrel's.
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