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Re: Pectoral Girdles



DSmith wrote:

>I have a question regarding the pectoral girdle of Archaeopteryx - a few
>actually.
>
>1)  As this is often referred to as "the first bird," did it possess the
>standard bird-like pectoral girdle (fused clavicles+interclavicle=furculum,

It possesses what has been interpreted as a furcula

>large coracoids articulating with the sternum (did it even have a sternum?),

The specimens show no ossified sternum

>blade-like scapula oriented parallel to the spinal column), or did that come
>later?

The shoulder joint is intermediate between some coelurosaur dinos and birds
(Jenkins 1993). _Archaeopteryx_ did not have the full range of movement
that modern birds have - for instance _Archaeopteryx_ could not raise its
arms over its back as modern birds can.

>2)  If the bird-like shoulder girdle came later, what, then, was the form of
>Archaeopteryx's?

See above. The question of "later" is tricky. _Archaeopteryx_ may not
represent the direct line to modern birds, but an early offshoot. In that
case the development of the shoulder girde in the direct lineage may have
progressed beyond that shown in _Archaeopteryx_ by the Late Jurrassic, but
we have no information on that.

>3)  If Archaeopteryx DID have the bird-like girdle, what other dinosaurs do
>we find this in?

Some theropods do show advancements similar to that in _Archaeopteryx_,
e.g. _Deinonychus_.

Chris

Jenkins, F.A. (1993) The evolution of the avian shoulder joint. American
Journal of Science, 293A: 253-267.


cnedin@geology.adelaide.edu.au                  nedin@ediacara.org
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Many say it was a mistake to come down from the trees, some say
the move out of the oceans was a bad idea. Me, I say the stiffening
of the notochord in the Cambrian was where it all went wrong,
it was all downhill from there.