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A Few Thoughts on Dinosaur Metabolism Strategies



A few thoughts on endothermic dinosaurs.

It is now well known that not all dinosaurs were raging warm-bloods.  Some,
such as duckbills, had high, warm-blooded metabolisms as youngsters, and when
they were fully grown their metabolisms became significantly slower, yes?
 This may have applied to some other voluminous dinosaurs, such as the
sauropods and ceratopians.  Animals with large mass, these dinosaurs, may
have been able to get most of their internal heat from the environment, like
in "reptiles."  Perhaps complicated internal mechanisms could keep this heat
inside the body when necessary, and on other occasions let the heat escape
from the body.  

Maybe some kinds of dinosaurs, maybe all, were a little bit of both
(ectothermic, endothermic).  Suppose they USUALLY got most of their heat from
the environment, externally, and also posessed the ability to keep in and
withdraw heat when necessary. Some kinds of dinosaurs may have generally
posessed low metabolisms when there was plenty of external heat to soak.  But
suppose if, such as during wet seasons, the dinosaur's body got completely
drained of heat and there was no more heat to "consume".  Possibly another
internal mechanism, in cases like this, could start producing internal heat
until there was environmental heat to absorb once again.  In other words, the
dinosaur could switch over from ectothermy to endothermy according to
environmental conditions.  And if this worked, the dinosaurs having these
interesting mechanisms could be cold-blooded at one point and still operate
(aside from its metabolism and source of heat) like a warm-blood -- for
example, it would not move sluggishly, but have swiftness and agility like a
warmblood.  A sauropod in the ectothermic phase would still have a long, easy
stride, and it would still be able to react quickly and effectively to such
occasions as predatory attacks.  

Perhaps for the herbivorous line of dinosaurs, excluding the theropoda, this
kind of complicated metabolism strategy could have been evolved.  If it was
possible, perhaps with a little more explanation it might have worked.  This
way, the planteaters could still have much energy and not have to eat as
much.  It would in a way be the ecosystem's way of keeping food consumption
down so that the herbivores wouldn't starve themselves.

This may have worked not only for large dinosaurian herbivores, but also for
small ones.  The hypsilophodontids, for example, may have normally sat around
with low metabolisms, eating when necessary, and absorbed and emitted heat,
sometimes producing their own heat, according the the conditions.  If a
predators suddenly attacked, the hysilophodonts would run far away in a quick
burst of energy until the danger was gone.  Then they would sit around again,
eating and absorbing heat.

I doubt, though, that the theropods were like this.  The theropods, from
early on, may have had a nearly complete warm-blooded metabolism, maybe just
a little lower than the metabolisms of birds.  The first theropods, which
came before the first herbivorous dinosaurs (at least according to my
knowledge), may have been small-game hunters.  Small game generally includes
insects and small vertebrates.  Early insectivorous theropods, lacking the
whip-lash tongues of frogs and chameleons, would have to pursue their prey --
even with special adaptations for catching insects this would have been a
challenge of speed and agility.  The same with little mammals and various
other vertebrates.  To live under such an active lifestyle, the theropods may
have evolved fairly high metabolisms gradually, and even though they would
also have to catch more prey than otherwise, they could do so more
efficiently.  And we should not forget that small-game theropods (with bones
so small and fragile they very rarely got preserved) probably existed all
throughout the Mesozoic, on all corner of the globe -- just because we have
not discovered something does not make in an improbability.   (Thanks to
Stang for pointing this out to me!!)  Have there ever been suggestions that a
small-game predatory lifestyle in theropods may have contributed to the
development of flight?

As plant-eating dinosaurs grew more numerous, some of the small-game
theropods, of course, evolved to fill the niche of larger-game predator.
 Although most, if not all, of the herbivores may have had mostly low
metabolisms, it is possible, as I discussed before, that they may have been
able to nicely handle short or long periods of high or moderate activity.  In
other words, be able to defend themselves well from the high-metabolism
theropods.  During the short lenghs of time in which dinosaur predator and
prey interacted, the normally "cold-blooded" plant-eaters, being able to
handle activity for a short period of time, would be able to fight or flight
like a raging warm-blood until the danger was over, or of course until the
prey itself was killed.  So the plant-eaters were not disadvantaged according
to this scheme at all.  

The theropods, as they brought down their large prey (at least the theropods
that did so), would have been very agile and active as they fought their
equally active prey.  Ambushing it would take a little running.  If they
actually got to attack their prey before it would escape or fight back, the
biting and tearing and slashing would be rather energy-consuming.  If the
prey escaped, running after it again would take up energy, and energy would
have been wasted if the predators abandoned their chances.  If the prey
fought back, the predators would have to counter, dodge, find some way to get
back to deliver the final blow.  Sometimes the prey proves to be too strong
to kill.  Even if the theropods were warm-blooded, they may have found it
rather difficult and had a poor chance of bringing down their prey...

If the prey had one metabolism strategy, and the predator a completely
different one, is it possible that the ecosystem worked properly?  

Comments are welcome. Please do correct my misinterpretations; indeed, they
must be quite abundant!!

Raptor RKC (Rachel Clark)