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Re: dem bones



>From: "Considine, Blaise" <bpc.apa@email.apa.org>
 > Now my question is why can't you tell how the bones ought to be 
 > connected? ... Don't bones line up in one correct way? 

Not necessarily.  There are two basic problems: joints and breakage.

Joints: in a vertebrate, all seperate bones are attached by means of
joints.  There are many kinds of joints, but almost all involve
some amount of cartilege (or other connective tissue).  The result
is that the ends of the *bone* *itself* rarely match up exactly.
[The main exceptions I know of are the skull bones].  Secondly,
in the case of the ribs, the joints are actually rather narrow.

Breakage: well, this one is obvious - few fossils, even "complete"
ones arrive at the preparator completely without wear and tear to
the specimen.  What this can do to mathcing is quite obvious.
About the worst, and also one of the most common, is crushing
and flattening, which change the shape of the bones, sometimes
without leaving obvious traces of the alteration.
[To inderstand why this is so common: imagine a few thousand tons
of dirt and rock piled on top ...].

 > Couldn't you tell about the ribs from their curvature (or what is left 
 > after fossilization)?

Assuming the curvature is still unchanged, there is still the issue
of determining at what angle to attach the head of the ribs to the
vertebrae.  This can be tricky.

[And, having seen a number of fossils, crushing and flattening
can easily alter the curvature of ribs].


Note, I am not saying it is impossible - only that it takes great
care, and attention to small details.

swf@elsegundoca.attgis.com              sarima@netcom.com

The peace of God be with you.