[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]
Is it possible hair preceded feathers? I know hair usually isn't on the
dinosaur line, but remember pterosaurs allegedly had hair. I wonder if it's
possible that synapsids and thecodonts could have had a common ancestor with
some kind of hair. It's much easier to see a hair evolving into a feather
than a scale.
At 02:33 PM 7/17/97 EDT, brush wrote:
>Yesterday (16 VII 97) Nick Longrich commented about the convergence
>in down feathers and various plant seeds. Indeed, this is convergence.
>In the airlifted seeds a sail/parachute develops in down feathers there
>are spaces to trap the air for insulation.
> By the same token there are many 'feather-shaped' forms in nature; leaves
> and especially many ferns. Again this is convergence on a shape. Perhaps for
>a variety of functions. A structure like that is a good one to produce a large
>surface area at minimal weight. But it is convergence.
> Further the branching pattern in plants is produced in a completely
>different way than in feather (eg growth and assembly are very different).
>Certainly the material as about as different as possible.
> The problem again is one of langauge. We cannot ask if "the branching
> of feathers evolved for aerodymanics, not insulation...". Evolution does not
> entertain goals of this sort, no matter how attractive may be the adaptation
> of the structure for its function. It is, however, informative to ask what
> the common ancestor of feathers might have looked like, or how it evolved
> (eg what changes were necessary to move from structure A to subsequent
> strcutures B,C, and D.). Certainly there were functional differences that
> emerge from developmental sequence changes, incorporation of new
> regulatory or structural genes, etc.
> It is not surprizing to find things in nature that are 'feather-like'
> or 'down-like". These are the similies and metaphors of communication.
> They have little to do with science. "Hair-like' was used, for example,
> to describe the strcutures on Sinosauropteryx. But, they cannot be hair in
> the restricted defination a scientist uses. There are lots of 'hair-like'
> structures in both the natural world and in man-made products. Unfortunately,
> everyone is not always clear on these, perhaps finer, distinctions. But
> because something in 'down-like' says nothing about its internal structure and
>its history. When it comes to understanding fossil material, or many other
>structure, it is paramont to use the proper term. In fact, there are even
>hair-like structures on birds (modified feathers, eye lashes) but they are