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Re: Apatosaurus: Follow up



> Date: Mon, 11 Jul 2005 08:57:49 -0700 (PDT)
> From: Mike Limonite <taradosgon@yahoo.com>
> 
> While searching the web for a a site that would give me the correct
> names for the different parts of a sauropods vertebrae I came across
> DML posts from 2004 which had mentioned alot of the material that
> was in my post making mine for the most part redundant (and looking
> back at the Gilmore Monograph some of the information I gave was
> incorrect). However, I still have a couple questions.

Hi, Mike, nice to see some sauropod discussion on-list.  Regarding the
name so the laminae, the definitive paper is Wilson 1999, which
established the system that's been used all but universally since
then:

        Wilson, Jeffrey A.  1999.  A nomenclature for vertebral
        laminae in sauropods and other saurischian dinosaurs.  Journal
        of Vertebrate Palaeontology 19(4): 639-653.

Not to steal Wilson's thunder, but the system is actually
astonishingly simple, once you get over the long names.  (Which is
really the point of the system, and the reason it's caught on.)  Each
lamina is just named after the two things it joins.  Spine up on top,
centrum down below, pre- and post-zygs at the front and back, and
diapophysis and parapophysis sticking out the sides.  So if you have a
lamina joining (say) the prezyg and the diapophysis, it's a
prezygadiapophyseal lamina (or PRDL for short).  If you have a lamine
below the postzyg (i.e. connecting it with the centrum), it's a
centropostzygapophyseal lamina (CPOL).  And so on.  Anything that
doesn't fit into that scheme is just labelled and "acessory lamina"
and swept under the carpet :-)

Second thing: if you're interested in detailed _Apatosaurus_
morphology and species-identity issues, then you _must_ get the new
Upchurch et al. 2005 monograph, which is state of the art on that
taxon.  It's a marvellous piece of work in every way: ferociously
detailed, meticulously referenced and (not least) beautifully
illustrated:

        Upchurch, Paul, Yukimitsu Tomida, and Paul M. Barrett.  2004.
        A new specimen of _Apatosaurus ajax_ (Sauropoda: Diplodocidae)
        from the Morrison Formation (Upper Jurassic) of Wyoming, USA.
        National Science Museum Monographs No.26.  Tokyo.  ISSN
        1342-9574

> Also the significance of anterior projections on the cervical ribs
> of _Apatosaurus_ specimens in classifying them has been undermined.

"Undermined" as in "wiped out"  :-)

> However, the anterior projections seen on _A. excelsus_ and _A.
> ajax_ cervicals would offer a different muscle attachment point than
> the ventral processes seen in _A. louisae_ and some _A. ajax_ and
> _A. excelsus_ cervicals, unless anterior projections grow from these
> ventral processes as the animal grows wouldn't _A.  louisae_ have a
> completely different muscle structure than CM 563?  Which would also
> mean that CM 563 and YPM 1980, even being of the same species
> (_A. excesus_) had noticeable differences in cervical muscles?

That seems extremely unlikely, as the presence and absence of anterior
projections from the cervical ribs seems to vary along all sorts of
axes, e.g. ontogenetic or even along the neck of an individual.  More
likely, the muscle attachment sites are homologous in all cases; just
very hard to spot :-)

 _/|_    ___________________________________________________________________
/o ) \/  Mike Taylor  <mike@miketaylor.org.uk>  http://www.miketaylor.org.uk
)_v__/\  "One hour of life, crowded to the full with glorious action,
         and filled with noble risks, is worth whole years of those mean
         observances of paltry decorum" -- Sir Walter Scott.

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