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Summary, dinosaurs vs. mammals
I thank you for all answers and discussion about "dinosaurs versus mammals".
There are more angles to this topic than I anticipated! There seem to be no
answers though but most explanations are similar to my points 1-5 plus the
"military" principle; when you get the upper hand, it is very difficult for the
to catch up even with the same weapons arsenal! Maybe the question should
have been divided into two:
1. Why did the archeosaurs outcompete the protomammals in the Triassic?
2. Why were the by-then-evolved small mammals still outcompeted during
the Cretaceous, but eager to expand into all niches after the K-T event?
.When the discussions have ceased, I may try to compile a summary
when I have digested all contributions.
Here is some discussion that I found on the Internet regarding
(new vocabulary for me for warm/cold-bloodied! I do not remember the site, I
find out again if someone is interested. Metabolism is my own favorite candidate
for the supremacy of the dinosaurs by the way.
"Summary of the Debate:
The problem is far from solved, as you may guess from what you've
seen so far. N Many questions about endothermy and ectothermy in
modern animals remain to be solved, such as: "How did
endothermy evolve in mammals?", "When did it evolve in birds?", or
"What alternatives are there to simple endothermic or ectothermic
strategies?". There is much, much work to be done before a
satisfying answer is available; maybe that time will never come --
dinosaurs (except birds) are long
dead and gone; all we have left are bits of fossilized bone and some
poor modern analogs (birds and
mammals, or lizards and crocodilians).
Yes, it's a confusing and frustrating controversy, and the two
(among the many) diametrically opposed sides of the argument help
to make it even more complex. Are some of them missing
something that paleontologists outside of the debate see? Maybe.
There is strong evidence from both sides that dinosaurs in general
had a different physiology from either mammals or "typical
reptiles". Endothermy did evolve from ectothermy, and birds (endotherms)
did evolve from dinosaurs, which we know came from ectothermic ancestors
sometime in the distant past. Dinosaurs were quite diverse in size and form;
their physiologies must have differed as well, just like whales,
bats, and horses have different physiologies. We have found examples of
physiologies outside of the artificial "endotherm - ectotherm" dichotomy:
elevated metabolic rates and even homeothermy exist
in some species of sea turtles, sharks, pythons, tuna, and even insects.
Some mammals, such as the monotremes have lower metabolic rates,
and seem closer to an ectothermic condition. As long as
we do not understand endothermy and how it evolves, we have little chance
of understanding what animals were endotherms or not.
(The following is especially interesting/Soren):
And, above all, there is no reason why dinosaurs could not have
had some sort of intermediate physiology between endothermy and
ectothermy. In fact, it seems more likely than anything that they did have
some unknown sort of physiological system that worked
well (they did dominate the realm of the terrestrial vertebrates for some
170 million years!). Some dinosaurs could have been normal ectotherms,
and some could have been endotherms. Yes, it's a messy issue.
We'll close by listing the five main sides that paleontologists have taken
since the issue began. Feel free to make up your own mind who may be right!
Top Five Current Hypotheses
1. Dinosaurs were complete endotherms, just like birds, their descendants.
2. Some or all dinosaurs had some intermediate type of physiology between
endothermy and ectothermy.
3. We know too little about dinosaurs to hazard a guess at what their
physiology was like.
4. Dinosaurs were mostly inertial homeotherms; they were ectothermic
but maintained a constant body temperature by growing large. Small
dinosaurs were typical ectotherms, maybe with a slightly
elevated metabolic rate.
5. All dinosaurs were simple ectotherms, enjoying the warm
Mesozoic climate. But that's ok but many ectotherms are quite active,
so dinosaurs could be active, too. "
I have also put the same"dinosaurs versus mammals" question to
Dr Bakker on his "home page", I hope he will answer.