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Re: Where to draw the line.
> Dr. McIntosh pointed out to me that the presence
> of a forward expansion on the cervical ribs in _A.
> excelsus_ and the lack of the expansion in _A.
> louisae_ is a main characteristic that separates the
> two species. Since then I have become convinced that
> this can no longer be used as a trait to separate the
> two species.
Congratulations!!! You've hit the nail on the head.
Mathew J. Wedel & R. Kent Sanders: Osteological correlates of cervical
musculature in Aves and Sauropoda (Dinosauria: Saurischia), with comments
on the cervical ribs of *Apatosaurus*, PaleoBios 22(3), 1 -- 6 (15
A few random quotes...
"The absence of anterior processes of the cervical ribs has traditionally
been regarded as an autapomorphy of *Apatosaurus louisae*. However,
anterior processes are weakly developed or absent in some specimens of *A.
ajax* and *A. excelsus*, so this character is probably less diagnostic
than previously assumed."
"[...] we consider the taxonomic utility of anterior processes to be
"the presence or absence of anterior processes is probably not useful for
discriminating species of *Apatosaurus*."
> What are the characteristics that paleontologists look
> for to determine whether _Apatosaurus) material is
> that of _A. excelsus_, _A. ajax_ or _A. louisae_?
> (cervical differences or otherwise).
> -Michael Lima
Maybe there are none anymore. :-)
BTW, if there's a university near you, I'm sure the library is public. The
university libraries over here are public, just that the general public
doesn't know that. :-)
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