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Re: buncha die-hards ain't ya? (Dino heart)
> The morphology indicates that it had a high level of activity and
> isn't endothermic? Well, you can't exactly get a high level of activity
> ectothermic (and I have debated this at length before, if you check the
> archives, and don't incredibly care to again). And I don't think this
> was big enough to register for homeothermy (correct me if I'm wrong, and
> else could it be?). But, regardless, I have to say this: I told ya
Hi Caleb. Don't confuse function with metabolism. This is a sticky issue.
As has already been alluded to previously during this discussion, the
possession of a four-chambered heart can only tell us something functional:
that high pressure blood needed to go toward the head and body, while low
pressure blood had to be shunted toward the lungs. The typical reptilian
heart with "three" chambers (one could actually claim it has five) has a
single ventricle (that's the bottom portion of the heart for those
unfamiliar) which is highly convoluted. It does a pretty decent job of
separating oxygen-rich blood from oxygen-poor blood through a series of
contractions that shunt the blood into various "pockets" where it will then
have a strong chance of either flowing to the body and head or to the lungs.
Because the ventricle is not completely separated, the pressure of the
blood going to the head and body has to remain somewhat similar to the
pressure going to the lungs. If the BP gets too high, the delicate
capillaries in the lungs would burst, killing the animal.
If you position your head far above your heart, or you become bigger so that
you need blood to reach far away regions of your body, having a fully
divided heart separates the high pressure blood going to the head and body
from the low pressure blood necessary not to burst the capillaries in the
While most of the animals that have this four-chambered system today are
endothermic, there are ectotherms that have a four chambered heart. Thus,
this is a functional problem and not a linch-pin arguement for endothermy.
In fact, it has long been predicted that dinosaurs would have had a
four-chambered heart because of the problems of blood transport described
This having been said, perhaps possession of a large, four-chambered heart
MIGHT indicate a level of activity above that of typical terrestrial
ectothermic animals (tuna and sea turtles being weird exceptions because of
their environs). Also, endothermy simply means that the animal possesses
aerobic skeletal musculature (as opposed to the relatively anaerobic muscles
of most ectotherms) and can internally control its body temperature.
Therefore, an animal could be an endotherm but have a relatively low core
One of the vexing problems of dinosaur physiology (besides the fact that we
have no living sauropods, ornithopods, etc., to run on a treadmill) is that
both living outgroups have no sweat glands. How does a naked-skinned
sauropod manage to cool itself effectively without an integumentary covering
or a large mouth from which to pant out heat? Sure, the long neck, tail,
and legs could have served as cooling towers, but even here this might not
On the other hand, a large ectotherm with no internal mechanism for temp
control and anaerobic muscles might find itself in a worse predicament.
Without aerobic muscles, a large ectothermic sauropod would have had a hard
time moving around without quickly exhausting itself. Futhermore, without
an internal means of temp control, just where does a large ectothermic
sauropod hide when it gets too hot?
Hence, this is why finding the first concrete evidence that at least some
dinosaurs had a four-chambered hear in no way helps us resolve the
physiological abilities of dinosaurs, but mostly supports the functional
hypothesis that dinosaurs had four-chambered hearts because of a necessary
division of blood pressure.
I end by saying that I think all dinosaurs were endothermic, but only in the
limited sense I describe above. Having very little concrete evidence to go
on, we are unfortunately stuck in a stale mate for now. Beyond that, who
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