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Re: proteins, feathers, and scales




On Wed, 13 Dec 1995 NKING.UCS@smtp.usi.edu wrote:

> 
> Imagine, for the moment, that scales evolved into feathers.  That 
> involves quite a structural change.  Couldn't such a change also have 
> involved a change in proteins?  After all, all cells in an organism have 
> the same genotype, hence are potentially capable of producing any protein 
> found in the animal.  With structure changing so much, couldn't the 
> dominant protein change, too?

        This isn't really likely, it seems, because there are structures 
that do not resemble scales but do closely resemble feathers, mainly, 
beaks, claws, and scutes. I have never understood any of this prior to 
all the recent E-mails, but I'm beginning to get it... As I understand, 
we're looking at feathers as probably being exapted from scutes- or did 
they just sort of spontaneously arise from the same materials as a truly 
novel structure?
        Scutes (somebody correct me if I'm wrong here) range from the 
little pebbly things on a duckbill's sides, to the larger, flat platelets 
a few centimeters across also on some duckbills and I think 
ceratopsians, too, to the small armor 
platelets on crocs and some thyreophorans, and finally to the large armor 
plates of the nodosaurs and stegosaurs. Bird scutes are the large, flat 
scaly things on top of their toes and feet. Basically, they are analogous 
but not homologous to scales on lepidosaurs. (I'm wondering, are those 
large scale-like things I see running down the back of an iguana in rows 
scutes or just large scales?)

        I'd like to ask about the T. rex skin found a little while back- 
all I can remember was that it was described as leathery and sort of like 
an elephant's in texture. Did it display the sort of pebbled texture 
found in duckbills? I'm wondering basically if it's possible that the stuff
could have supported feathers. After all, IF these Pelicanimimus
"integumentary structures" are primitive insulatory feathers, then it
would seem possible for tyrannosaurs to have them as well- seeing as the 
last common ancestor of ornithomimes and birds is also the ancestor of
T. rex. Other possibilities include- T. rex is secondarily featherless
or only partly feathered, or that the Pelicanimimus stuff is not feathers.
        I am by no means convinced that Pelicanimimus is feathered, but I 
sure am eager to be convinced...

        -nick L.