Re: Pelecanimimus and Sinosauropteryx

[Jeffrey Martz <martz@holly.ColoState.EDU>]

> Olshevsky had a theory that bird feathers developed from a double row of
> ornamental scales on the back of arboreal archosaurs. By the time of
> Sinosauropteryx, those scales were well on its way of becoming feathers
> (Developing as display or insulatory elements from the top midline of the
> animal downwards).

       If you look at the way a feather develops in a bird's skin, you
don't see "ornamental scales".  The protofeather begins as a sort of
"hair" (what later serves as the rachis) before developing (at least in
contour feathers) barbs and barbules.  The fact that feather development
starts out exactly like a scale before differentiating into the lone 
rachis implies to me that this is a case of ontogeny
recapitulating phylogeny.  Someone who knows a little more about feather
development may care to debunk this, but I think the best model for an
early feather is a "hair", not an ornamental scale.

LN Jeff
O-