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RE: [Re: Feathered/scaly theropods: trying to make the point.]



-----Original Message-----
From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of David Marjanovic
Another point, how would you explain that the integument of birds where
preserved correctly, while that of (nonavian) dinosaurs wasn't?
In my last e-mail I forgot to add that AFAIK the feathers of Liáoníng birds and near-birds look the same (haven't seen specimens), and that even the feathers on the various pieces of "Archaeoraptor" are genuine!
 
Concerning secondary featherlessness and tyrannosaur scales -- what about a single mutation that produced scutes all over the body instead of only on the feet?
 
Actually, something very similar to this mutation is present in modern chickens (they retain some feathers on the body, but look pretty darn weird: saw them at the SICB Feathers meeting  back in 1999).  However, let us remember that we most certainly do not yet know what the integument of all parts of the body of a tyrannosaurid looks like (okay, to be fair we don't know for certain what any of it looks like, until such time as the tyrannosaurid skin impressions are presented in some sort of non-internet context where people can evaulate them and see what they look like).
 
I would not put it out of the realm of reason for there to have been scales in some areas, scutes in others (the feet), and scaleless skin in still others.  We already know that the size and shape of scales in hadrosaurids (for example) vary from different parts of the body, and furthermore we have examples of modern theropods with naked heads, feathered bodies, and scute-covered feet.
 
Even further complications in reconstructing the physical distribution of feathers on a given form:
    *Feathers change in type (and in some cases distribution) during ontogeny
    *External appearances to the contrary, feathers do not sprout out all over the surface of a birds body in the majority of modern birds.  Thus, feathers of modern birds are NOT arranged like mammalian hair.  Instead, they actually arise out of several tracks down parts of the body, but based on their orientation from these tracks manage to cover the surface of the bird.  It would be interesting to find out if Mesozoic coelurosaur feathers similarly grew in tracks, or if instead the basal condition was more like hair in its anatomical distribution, and only later became sequestered into certain parts of the skin.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742      
http://www.geol.umd.edu/~tholtz/tholtz.htm
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