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Re: more about "feather" find
--- On Wed, 3/18/09, David Marjanovic <email@example.com> wrote:
> > It says that a fossil of a small dinosaur of the
> saurichian line was covered
> > with long very primitive feathers.
> No, it's an ornithischian, and that's part of why
> it's such a surprise!!!
Didn't some types of Psittacosaurus have quills on their tail?
> > Have any of you looked closely at the fur of a cat?
> Some modern mammals
> > could be said to have very primitive feathers.
> Less so than *Tianyulong*. *Tianyulong* has pretty stiff
> bristles that were half a millimeter thick -- that's
> more like the keel of a feather than like a hair.
> "They were very gently curved but otherwise rigid - no
> bends or waves were found."
Sounds like they resembled the quills on a porcupine (sans barbs and a pointy
tip) more than fur or fuzz.
Feather shafts and mammalian quills seem similar in many aspects.
> > When did synapsids develop their fibrous body
> The docodont *Castorocauda*, closely related to
> Mammalia-in-the-strictest-sense, had fur, but beyond that we
> don't know. The dinocephalian *Estemmenosuchus*, a
> Middle Permian animal, appears to have had naked skin.
> Somewhere between these two, then... that's a lot of
But *Estemmenosuchus* was a rather large animal. As far as fur goes, smaller
animals need it more due to surface area/volume ratios.
If a future civilization were to only find impressions of Rhino/hippo/elephant
skin, might they conclude fur had not yet evolved in mammals? what was the size
smallest discernible detail on the impression that is used to conclude
*Estemmenosuchus* had naked skin, and how does that size compare to the size
you would need to see the hair present on elephants/rhinos/hippos today?
Assuming pelycosaurs had sails for temperature regulation, and assuming
dinocephalians evolved from earlier pelycosaurs, I would assume the best
explanation for sail loss is an ability to regulate temperature similar to how
mammals do today - rendering the sail useless and detrimental (as it would make
the animal much easier to see).
It seems likely fur would evolve around the same time temperature regulation
via internal heat generation did.
I wouldn't be convinced until there is evidence smaller synapsids of that time