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Re: what are gastralia?



>Lambert's book "The Ultimate Dinosaur Book" has a short sentence saying that
>belly ribs are gastralia..with no more explanation.  What are they?  What
>were they connected to?  What animals were they found in?  I've never noticed
>them in any drawings or reconstructions...maybe I haven't looked hard enough.
> Any information would be appreciated.

Marilyn et al -

        Gastralia, also called "belly ribs," are just that:  small, thin,
rib-like bones that line the underside of the gut.  Take a good look at
your average theropod skeletal reconstruction (Greg Paul's always have
them) and, just beneath the ribs, you'll see them.  They aren't attached to
anything (in the sense of having condyle-cotyle relationships with nearby
bones), just embedded in the muscles there.  (Don't act surprised!  8-)
Not all bones are attached to each other.  In fact, in those same
dinosaurs, the entire pectoral girdle and arms aren't attached to any of
the rest of the skeleton, either!  They're only connected by muscles!)

        Of course, when you look at them in a side-view skeletal drawing,
you aren't seeing what gastralia _really_ look like:  they're sort of
shallow parabolic arcs consisting of two "ribs" fused at the midline.  They
are found primarily in theropods, although they've also found a sauropod
with them  (the new _Apatosaurus yahnapin_, or however that's spelled!)
Since they aren't connected to anything, and they're small, comaratively
lightweight bones, they're easily lost when an animal's body breaks up
prior to fossiliziation, and may be present in more animals than we know of
yet (specifically, other sauropods)...



Jerry D. Harris
Denver Museum of Natural History
2001 Colorado Blvd.
Denver, CO  80205
(303) 370-6403
Internet:  jdharris@teal.csn.net
CompuServe:  73132,3372

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