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Re: Origin of Feathers



    As I once indicated, based on personal communication with Jack Horner,
he believed - because he feels that it makes sense - that _Maiasaura_ babies
had downy feathers until they reached a certain size (or age).  He has yet
to find any feathers of any kind in the _Maiasaura_ nests.

    My problem with this is the same as yours, Ralph; how come we don't see
evidence in the skin?

    Allan Edels

-----Original Message-----
From: Ralph Miller III <gbabcock@best.com>
To: Jaime Headden <jaemei@hotmail.com>
Cc: Dinosaur Mailing List <dinosaur@usc.edu>
Date: Friday, May 08, 1998 12:55 PM
Subject: 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
>true.
>
>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
>
>