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RE: Brooding rex? (was Feathers for T. rex)



 
Tom Hopp wrote:

>So the presence of scutes/scales on large theropods rules out feathers?
>Why? Armadillos and pangolins have scutes with hair between them. You're
>saying large theropods had scales/scutes ONLY, but that's not >necessarily
true.
>Absence of evidence is not evidence of absence.

Very Ostrom-esque :-)

This topic has been discussed previously on the list, mostly between me and
the DMLer named "Jura".  Jura argued that scales/scutes and feathers could
not coexist on the bodies of theropod dinosaurs.  I argued that there is no
reason to assume that feathers and scales/scutes were mutually exclusive.

The naked patches (apteria) between the feather tracts (pterylae) in modern
birds may originally have been scaly or scuted.  Alternatively, the feathers
(or their direct precursors) may have been arranged in a random, non-linear
fashion alongside scutes and scaly patches - which would make the
"neat-and-tidy" feather tracts more derived than the existence of feathers
themselves (and perhaps were associated with flight).  

Most modern birds (adults) have feather tracts (pterylae) separated by naked
skin (apteria).  In many adult anseriforms the apteria are not naked:
plumules (down feathers) are expressed in the regions between the tracts.
(I think loons/gaviiforms have this as well - probably associated with the
need to keep warm when paddling on or through water).  Some flightless birds
(ratites, penguins) do not have pterylae at all, with the contour feathers
(or their derivatives) arranged in a fairly random, uniform fashion.  At
least one group of flying birds (anhimas or screamers - bizarre anseriforms
once regarded as galliforms) also lack pterylae.  It is interesting to
consider which state might be primitive for the Neornithes - and for more
inclusive clades.  Is the presence of pterylae primitive or derived for the
Avialae / Neornithes / Neognathae?  

By the way, is there any chance of seeing the brooding --> flight hypothesis
in print?



Tim


------------------------------------------------------------ 

Timothy J. Williams 

USDA-ARS Researcher 
Agronomy Hall 
Iowa State University 
Ames IA 50014 

Phone: 515 294 9233 
Fax:   515 294 3163 

n