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Re: New in Nature: Birds Galore!



----- Original Message -----
From: "ekaterina A" <a_ekaterina@yahoo.com>
Sent: Thursday, January 23, 2003 7:37 AM

> To me the feathers on the Hind limbs are not
> surprising : it is merely a case of serial homology.

To me, this is surprising: dinosaurs are famous for reducing serial homology
between hands and feet, as seen by the symmetrical digit reduction of the
feet and the asymmetric one of the hands.

> The recent work has shown that feather
> development appears to be regulated by a pattern
> forming field of Sonic hedgehog and BMP2. Now, these
> pathways are even more  ancient as they even function
> in the mammalian hair follicle's formation.

I forgot which Bmp is involved in limb formation, but Shh appears to be
involved in all outgrowths of the body wall. Without it (vertebrate) limbs
form (sort of) but stay in the body.

> This fossil
> Microraptor pauli appears to have precisely captured
> this stage in evolution.

And kept it for a few tens of millions of years?

> Subsequently natural selection allowed
> the origin of specific pathways that restricted
> this kind of feathers to the fore limb only.

Subsequent? Somehow contradicts the above, doesn't it?