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Re: Origin of Feathers

Speaking of feathered dinosaurs, I wrote:
> <Why stop there? Don't you find fuzzy little hadrosaur chicks 
> appealing?>
Jaime A Headden wrote:
>   I understand you meant this as a joke, but I've actually considered 
> it, and though I've discarded the idea as very likely, and as 
> ornithschians are quite well separated from avian evolution, it _does_ 
> have it's appeal, and I almost drew a downy maiasaur chick (I still 
> might!) and Greg Paul has drawn dryosaurs with feathers or such similar 
> covering.

Yes, this was meant as a joke, but a joke that may have a chance of being

Assuming a homology between protofeathers and bird feathers, the more
parsimonious approach may indeed be that a good many theropods had some
kind of feather or protofeather integument (at least at an early stage in
their lives), considering the phylogenetic distance between
_Sinosauropteryx prima_ and birds.  On the other hand, as far as I know
there are no good fossil tubercle impressions of small or baby dinosaurs of
any kind to tell us what integument was typical for the other dinosaur
groups, so feathers of some kind may have been widespread.  Perhaps, among
the larger theropods (and perhaps, by extension, among all non-avian
dinosaurs), the feathers were shed as they grew and took advantage of mass
homeothermy.  We certainly know that _Canotaurus_, among others, had
tubercular skin as an adult.

This brings me to a puzzle which needs some attention.  As we know, animals
may go through profound changes as they develop from infancy to maturity. 
But how likely is the above scenario, whereby a fully feathered non-avian
dinosaur loses feathers as it grows, and arrives at a scaly (tubercular)
skin upon reaching full size?

I am aware that some birds are rather more luxuriantly feathered than
others, and that some, such as the aforementioned (extinct) upland moa, as
well as the ptarmigan and the snowy owl, have feathers which extend much
further down the leg and/or foot than other birds do.  But in the case of
the upland moa, a smooth skin exhibiting an absence of scales has been
noted wherever the feathers covered the skin on the legs, in contrast to
the scaly skin exhibited by unfeathered bird legs.  Ostrich leather
(presumably from the thigh region?) has an interesting bumpy texture, but
does not match the polygonal tubercle pattern observed in dinosaur skin
impressions.  It is unclear to me whether a dinosaur could shed feathers
and leave behind a typical dinosaur skin.  The question of how feathers
arise from the skin of dinosaurs and birds would seem to bear on what is
left if the animal (hypothetically) sheds feathers as it matures. 
Comments, anyone?

-- Ralph Miller III     gbabcock@best.com