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Re: hypocleidium (an interclavicle???)
Ken Kinman (firstname.lastname@example.org) wrote:
<Is the hypocleidium found in nearly all Pygostylia (or are there a lot of
exceptions?), and is it
homologous to the "hypocleidium" found in Oviraptor and Bambiraptor (any other
And are either or both of these homologous to the interclavicle (or is that
an old idea that
has definitely been disproven)?>
No memeber of the Dinosauromorpha possesses an interclavicle. This is a
distinct osseous element
that interjects between coracoids and between each of the clavicle bones; the
interclavicle has a
tri-radiate morphology, essentially Y-shaped in form, leading to the confusion
I'm sure that
spawned the question. In the period of time that the dinosaurian furcula of
offered as an interclavicle since Osborn's 1924 description, it has since been
scientific conclusion that this element is in fact a fusion or collection of
two clavicles without
an interclavicle, and no the interclavbicle itself. Even as recent as 1986, the
fusion of the
clavicles was regarded as "fused clavicles" and not a "furcula," and is still
regarded as such by
the more resistant of the ornithologists (see Feduccia, 1996, for example).
The hypocleidium is a structure that appears early in the development of
furculae, appearing in allosauroids and tyrannosauroids, as a distinct process.
It appears to be
an extension of the fusion of two diaphyses, such as the ramal shafts of the
paired clavicles. It
is lost in early birds, such as *Archaeopteryx* and *Confuciusornis*, but is
derived in higher
groups, so that nearly all modern birds possess it. Rather than re-expression,
it is likely that
the hypocleidium in higher birds is probably a neomorph structure adapted based
attachment, rather than the ends of two fused diaphyses.
Jaime A. Headden
Where the Wind Comes Sweeping Down the Pampas!!!!
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