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Re: Kneecap



Martin Baeker (martin.baeker@tu-bs.de) wrote:

<did dinosaurs have kneecaps or were these invented by mammals/synapsids?>

  Yes, birds have a patellar ossification, usually fused to the tibia as
part of the cnemial process, but essentially a secondary ossification from
the proximal tibia. I possess a few avian patella incompletely fused to
their respective tibiae, but I found this out before getting these bones
so it was no surprise. The cnemial morphology of most dinosaurs is not in
keeping with such an ossification if we were to infer it would exist in a
bird-like knee. But that being said, animals WITH bird-like knees include
maniraptorans such as alvarezsaurs, which have complex cnemial processes,
and troodontids, which are more "bird-like" in their tibiae it seems than
are dromaeosaurids. None of these animals have been found with patellae,
but it's not out of the question. None of the Las Hoyas, Patagonian,
Yixian or Jiufotang birds have patellae at least as far identified. Such
ossification appears to have been absent in pre-avian archosaurs, so it is
almost astoundingly clear that this is a convergent development. The
purpose differs, though, as the muscles and tendons of the mammalian knee
differ strongly from that of the avian knee, though they both seem to help
the flexed-knees of most mammals and birds relatively well; birds fuse
their knees at maturity, whereas mammals do not. So it is likely the
functions were drastically different.

  I found this casual rummage:

 
http://www.soldaat.com/edward/seabirds_skulls/Osteology/Seabird%20Osteology/legs%20of%20seabirds.htm

  and this recent paper (which I do not have) may also help:

  O'Rahilly, R. and E. Gardner. 2005. The development of the kne joint of
    the chick and its corelation with embryonic staging. _Journal of
    Morphology_ 98(1):49-87.

  Cheers,


Jaime A. Headden

  Little steps are often the hardest to take.  We are too used to making leaps 
in the face of adversity, that a simple skip is so hard to do.  We should all 
learn to walk soft, walk small, see the world around us rather than zoom by it.

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


                
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