Re: Skin

[Lars_Bergquist@public.se (Lars Bergquist)]

On 95-02-11 at 19.21, ornstn@hookup.net wrote:

> Secondly, even if pterosaurs did have hair this does not mean that
> pterosaur and mammalian hairs are homologous structures (the two
> groups are only distantly related), and for that matter hair or
> something like it can be found on bumblebees and even plants. 
> Perhaps the statement should read "one of the distinctions of being
> a mamma[l] is having MAMMALIAN hair...

Well, that's more like it! Come to think of it, bumblebees have legs
too ... and they _are_ legs though not homologous of course. However,
I was just asking about hair--not _homologous_ hair, just plain
functional fuzz.

But seriously--though large animals in warm climates can keep cosy
without insulation, small ones in cool climates do need it. Of course
"insulation" does not necessarily mean hair--or feathers, to return
to that subject. A nice layer of blubber will work too. My point is
that though we do not know much about dino thermoregulation, it is
clear that it must have existed if the beasts had body temperatures
much above ambient. And regulation achieved just by adjusting the
thermostat up and burning more energy is so wasteful that I cannot
readily think of any homoeothermic animal which uses this method. 
Small pterosaurs rotund with blubber is an intriguing idea, but no ... 
the weight penalty would be too great. Remember, fat is OK when
you're swimming and it just gives you extra buoyancy, but hair or
down is lighter, because the actual insulating materia is air. Much
better for flying!

Of course dinos probably did not run at 37 C. But flight is a very
demanding excercise. Remember those large moths that have to
warm up their flight muscles by vibrating them before first take-
off on a cool morning!

Lars Bergquist
lars_bergquist@public.se
(lexicographer ... "a harmless drudge" according to Dr. Johnson,
so bear with me)

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