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Feathers, insulators, reasons for both
At 01:13 PM 10/8/96 -0500, firstname.lastname@example.org wrote:
>If this were so, I would have expected animals living in cold
>conditions to have evolved hairs mimicking feather structure. But as
>far as I know (and I'll probably be told otherwise!) they don't; what
>they do evolve is different hairs in different densities. Feathers are
>good insulators, sure, but I don't see how they can be "better".
I need to consult a textbook, but right offhand, I don't see how
you've proven anything. Evolution does not always come up with the same
solution. Mammals increase their feather density. Do birds? I doubt they
increase it that much, but, like I said, I need to look this up (after I've
finished my three-layer subsurface map project).
In any case, to really find out, we need to either measure number of
feathers/unit area or number of hairs per unit area, or perhaps more
importantly, mass of feathers or hair/unit of insulated area for animals
with similar activity regimes in similar environments, and come up with a
numerical statement. Until then, I will go with the material science
explanation and suggest that feathers are, one for one, better insulators.
George Olshevsky wrote:
>Feduccia gives excellent evidence in support of the thesis that feathers
>evolved for flight, and that contour feathers are modified flight feathers
If his evidence is the presence of a rachis, this will become
>rather than vice versa. Yes, the evidence includes _Longisquama_ and its
Although I am certain he would never suggest a four-winged flyer...
>"pre-feathers." For example, there's the central rachis of the feather. Why
>is it there? To stiffen the feather, for one thing. And why stiffen the
>feather, if all you really need is insulatory fluff? To support the animal
Or it was exapted from a structure already in place. If feathers
did in fact originate as feathered scales, perhaps the rachis was to retain
some structural strength. One would want some sort of support structure for
the feathers anyway, to keep them somewhat orderly. Why do so many mammals
have stiff hair? It isn't so they can fly...
>And, since contour feathers are not for flying, why do they have a
Because it is a part of the feather structure, which happens also be
useful for flight. It certainly does no harm to retain this feature.
Besides, why would contour feathers develop a rachis if they are never being
used for flight? Does Feduccia think that birds used to flap their chests?
Please, no one go here, ok?
Do rattites have rachi [sic?]?
>Because they retain it from when the feathers first formed for
>flight. Etc., etc.
Doesn't hold water with the evidence you have presented.
>Much of Feduccia's work strongly supports BCF (that's one reason I keep citing
Hadn't noticed... :)
>Active I would agree, but that doesn't imply endothermy--just a good
>circulation with a quadricameral heart. As far as jumping on bandwagons, I
Sorry. I am aware that you actually pipe up about BCF on most
topics, and it just seems like you are jumping on the bandwagon because you
get especially excited when evidence does not have to be excessively
interpreted in order to fit your theory.
>wrote about dinos and avian ancestors as possible active ectotherms in both
>previous printings of _Mesozoic Meanderings_, viz., that dinosaurs had some
>kind of intermediate physiology, neither fully ectothermic nor fully
>endothermic, and that endothermy must have evolved in stages rather than
>springing up suddenly overnight.
I cannot see where it is necessarily valid to conjure some
"intermediate metabolism" from the depths of the imagination in order to
explain conflicting data. This is the same problem you run into with BCF.
Faced with conflicting evidence, you assume that the most parsimonious
conclusion is somewhere in the middle, creating, in that case, an entire new
line of animals for which there is minimal fossil evidence, and then
claiming that it is the most parsimonoious conclusion. Or, in the case of
metabolism, you create an entirely new metabolism for which we have no
evidence other than conflicting evidence for two other metabolic
regimes(yes, it has been mentioned by scientists, but to them it is a
hypothesis, which they test, or just idle speculation...).
Both of these theories violate Occam's Razor. They require the
assumption of things for which we have no proof and no direct modern analog.
And yes, I am aware of intermediate metabolisms, but I have not heard any
which tidily reconcile all of the available evidence. This is science, we
don't look for quick fixes, we don't seek to tidily reconcile everything
all the time, we look for evidence and hypotheses and theories, and
sometimes data just don't fit. Sometimes, we do find some way to explain
most of the conflicting evidence, but neither of the theories I have
mentioned above do this. Voodoo evolution just isn't going to cut it.
So, we come back to... dinosaurs could have needed insulation.
| Jonathan R. Wagner "You can clade if you want to, |
| Department of Geosciences You can leave your friends behind |
| Texas Tech University Because your friends don't clade |
| Lubbock, TX 79409 and if they don't clade, |
| *** email@example.com *** Then they're no friends of mine." |
| Web Page: http://faraday.clas.virginia.edu/~jrw6f |