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Folding Feathers Out of the Way



Rob Gay wrote:
 
<And on feathers and dinosaurs, the other day, there
was some discusion about early birds not wanting to
potentialy damage their primary flight feathers by
climbing.

...

What interested me, though, was that these birds,
leaping and biting on the carcass, seemed not too
concerned with their feathers. In some cases, vultures
were actually standing on vultures, and biting at each
other. I think (Key words, "I think") that if modern
birds subject their flight feathers to this type of 
harsh abuse, then I do not think (Once again, my
personal opinion) that it would be unreasonable for an
early bird to climb trees with its forelimbs.>

  Luis originally hypothesized a couple months ago
without discussion. However, he never suggested the
animals did not use their arms to prevent damage to
hypothetical remiges (or whatever others feathers on
the arms they might have had).

  Basically, though, I would think it was be extremely
difficult for these animals to climb without the use
of their arms. So, either they _did_ climb, or not. If
they did, did they sport feathers, or not? If they
sported feathers and climbed, how would they have kept
from damaging the feathers while climbing? That was
the bulk of the hypothesis. You can test this in a
multitude of ways, but to Rob Gay's observation, the
vultures were not standing on their own feathers, so
were not willingly doing anything to damage them.
Additionally, they were not climbing with their arms.

  Hoatzin (*Opisthocomus*) chicks have very
rudimentary remiges, and clamber about like the little
avian monkeys they are ("Aviprimates"?); thing is,
take the proportionate size of the remiges in hotazin
chicks and apply it to dromaeosaurs or oviraptorids,
and these are big enough to be useful in display
whether they were patterned or brightly colored or
solid. Further, the remiges in the chikcs do not
contact one another along their lengths except at the
shoulder joint and the wrist (primary/secondary
margin) and so if used as an umbrella (sensu Hopp and
Orsen, 1999; Clark et al., 1999) they would have let
some heated light through, but reflected maybe more
than 60% (I'd have to due calcs, so will try later) of
the heat-bearing light, and that may still have fried
the eggs.

  So, oviraptorids and dromaeosaurids may have borne
entirely different (or none) brachial appendages.
*Caudipteryx*, a proposed oviraptorosaur or close
relative (also, bird affinities have been suggested --
Feduccia, 1999) at least as a maniraptoran, has
complete layered remiges and applying such a structure
would support the hypothesis of an umbrella.

  However, and getting back to Luis' hypothesis and
Rob's observation, how these feathers orient to the
arm is a question that will go towards testing the
original question, and perhaps the feathers would
never have been in danger during climbing, or they
would have folded relative to the long bones of the
arm, which as I understand it there is no correlate or
structure to suggest this was possible in the avian or
maniraptoran (sensu stricto) arm.

  Anybody have further comments? You bird guys out
there should have some data on the feather/arm
articulation that would clear some of the questions.

--------

Jaguars and thecodonts later, gotta go to work.

=====
Jaime "James" A. Headden

  Dinosaurs are horrible, terrible creatures! Even the
  fluffy ones, the snuggle-up-at-night-with ones. You think
  they're fun and sweet, but watch out for that stray tail
  spike! Down, gaston, down, boy! No, not on top of Momma!

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