Re: Cold Blooded Dinosaurs

JTEM wrote:

John Harshman <jharshman.diespam...@xxxxxxxxxxx> wrote:



JTEM wrote:

John Harshman <jharshman.diespam...@xxxxxxxxxxx> wrote:

Well of course they serve another important function.
Several of them,in fact. But your claim doesn't
follow from that.

As does the fur on most mammals....

I maintain that all other functions are secondary. Do
you disagree?

I certainly disagree with the idea that you have any
way of knowing. Insulation may be common, even important,
but it may not be critical.

What other primary function do you postulate?

Note that it's possible for hair to have evolved
originally for another function -- say, as vibrissae -- but
we're not arguing about the evolutionary origin of hair
and feathers here, but about the origin of body coverings
of hair and feathers.

Oddly, I would think that logically (and I am aware that
evolution thumbs its nose at our idea of logic),
color/body markings are the likely catalyst. My guess is that
it was easier for animals with body coverings to change
colors & markings -- adapt to environments/seasons/display --
than animals without body coverings.

That seems very unlikely to me. Why should feathers be better at this
than scales? (And of course many lizards can change color in seconds,
without a great expenditure of energy.)

A patch here and there is one
thing, the body covering another.


Agreed.


The question is where the evidence we have points.


...but only after carving away inconvenient evidence.

The fact that some mammals are bald is evidence, evidence
that is set aside in order to pretend that the evidence
all points to something else.

I wouldn't consider that evidence. Your point is backwards. We're trying
to figure out why coelurosaurs had feathers covering their bodies.
Saying that some mammals don't have hair doesn't seem relevant. We know
that hair and feathers are used as insulation in many species. And we
also know that almost all of the hairless mammals don't need hair for
the simple reason that they either have other forms of insulation (e.g.
blubber) or don't need it because their size renders cooling the major
problem.

By the way, I would think that the extra function you're looking for --
why there are no bald birds -- would be obvious: flight. It's both
developmentally easier to retain contour feathers while retaining flight
feathers and functionally useful to have feathers smoothing the body
contour to lessen air resistance.

But my point is that this is irrelevant, since it can't explain the
evolution of body feathers in flightless theropods.

All you have managed to say is that the evidence for
endothermy is not conclusive.

True. But I am correct. The evidence demonstrates that as
important as thermal regulation is, there's something
more important.... else we would see at least some species
of bald birds.

No, the evidence demonstrates no such thing. At best it's an extremely
weak argument. Much weaker than the argument that feathers are useful
for insulation, and therefore suggest endothermy.

But it's still the way to bet, unless you have some
alternative that has better support.

That's not how good science works. Good science explains
the evidence, and not just the evidence that we cherry
pick.

Good science explains the evidence better than alternative explanations.
You have none so far. The best you have offered is a suspicion, for
which you present no evidence, that color change is the function for
feather evolution.

Clearly, I believe that we should see at least a few
bald bird species if insulation were the only factor.

Nobody says insulation is the only factor,

...in mammals as well as birds.

Correct.

but I don't agree with your premise anyway.


And neither do you allow inconvenient evidence to get
in your way.

That was a pointless jab. But let me congratulate you on sticking mostly
to real arguments that confront my arguments directly for the last
several posts. It's a refreshing change.

Let me summarize:

1. Body feathers are widely distributed in flightless coelurosaurs.
2. The obvious function for such a covering is insulation.
3. Other functions are either secondary in living species or are not
relevant to the intiial evolution of a whole-body covering (e.g. the
flight and vibrissae functions).
4. You have presented no alternative explanation that works -- color
change works for scales as well as feathers; perhaps better because it
can be done in seconds rather than weeks.
5. Therefore the evidence suggests that endothermy was present in basal
coelurosaurs.

.

Relevant Pages

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