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Re: Origin of feathers



<The problems with the brooding hypothesis are>
...
<(1) there is no compelling need to have the feathers on the arms, 
particularly since they would interfere with other useful forelimb 
functions, such as subduing prey (note the huge claws on the manus of 
_Oviraptor_); elongate, movable feathers exclusively for brooding can 
appear anywhere on the lateral part of the body;>

  But none too likely. Name me a bird that broods with feathers on the 
lateral surface of the body. While not disparaging the idea that yes, 
the brooder could have had brooding feathers on the sides, it is not 
unpresumptuous to say that yes, there could have been brachial feathers 
long enough to brood with, and even not interfere with the other manual 
or brachial motions of the arms.

  Many birds can adjust their feathers so they do not stick out, lay 
flat, etc. The ventral surface of the avian ulna is ridged, while 
*Oviraptor*'s (for instance) is not, and we already assume Archie could 
use his claws and fly (or ornithopt, or whatever). The ridge actually 
stiffens the quills, while a rounded surface would not provide any 
direct anchor for the ends. Thus, we can assume that a brooding dinosaur 
could actually tuck its feathers parallel to the arm, and never 
interfere with the manual motions.

  The only time I can see that the feathers and the manus would come 
into conflict would be when the manus was folded back, and the feathers 
were "fanned out". With the manus folded, this obviates any need to use 
it, thus the feathers could be in any position they like.

  Perhaps the arm was covered in contours and skin stretched between the 
extremities, as in a living bird?

...
<(2) the hypothesis doesn't explain other adaptations for flying and 
arboreal living in theropods, such as the proximally reduced, 
retroverted hallux and the stiffened tail, that don't have anything to 
do with wings.>

  The hallux is for perching or even grasping while the foot is off the 
ground.

  How does the bird get to the branch to perch (and why?) unless by 
climbing or by flight. Like a woodpecker, climbing is made easier by 
using a stiffened tail for balance, and the fourth toe is retroverted to 
make maximum gripping ability on the vertical surface. Whether Archie 
used his tail to help him climb up to gain an advantage point from which 
to launch off is considerable [something to consider]. 

<But if the feathers are already on the wings for another reason (such 
as flying), they can of course easily be exapted for brooding and 
related functions (shadowing, display, etc.). Wing feathers -> brooding 
feathers is easy, brooding feathers -> wing feathers is very unlikely.>

  I agree with this point, George. There is evidence, as I've posted 
before, to suggest that oviraptors and birds had a common ansector [and 
no, I don't want to get into another debate ... that comes later this 
month.... ;-)]. Presumably, that common ansector would have feathers. 
Being flightless, dromaeosaurs and oviraptorosaurs, and even 
ornitholestids and compsognathids would have had feathers, as for small 
therizinosaurs and ornithomimids, and troodontids, and perhaps the 
smaller tyrannosaurs (aublysodonts, and/or *Siamotyrannus* {14 feet, by 
my estimation} even if it proves not to be a tyrannosaur).

Jaime A. Headden

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