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Inconsistency in Apatosaurus traits/Strange metamorphosis



     The horse is dead but I am still beating it. In
my last post, entitled "Where to draw the line," I
mentioned a few differences from Apatosaurus species
to Apatosaurus species. I mentioned that I felt the
presence, or absence, of an anterior expansion on the
cervical ribs of Apatosaurus species cannot be
considered a trait which separates the species from
one another. However, it doesn't stop there. I have
continuously been looking over the the cervicals of
each species and have noted that most, if not all, of
the smaller differences are most likely invalid traits
as well, for separating the species. 

Trends in the cervicals (all references to A. excelsus
are based off of the U. of Wyoming specimen unless
stated otherwise):

*The postspinal laminae in A. excelsus is curved in A.
excelsus and in A. louisae it is straight. This cold
easily be considered an individual, age related, or
gender difference. 

*In the University of Wyoming A. excelsus (formerly
563), there is a ridge of bone, or lamina, that runs
from the posterior of the centrum toward the
diapophysial-postzygapophysial laminae on each side of
the centrum. This laminae forms a "<" shape of bone on
the left side of the centrum (when looking at the
cervical from a posterior view. As well as a ">" shape
on the right. Originally I considered this a trait
that could possibly be exclusive to A. excelsus from
A. louisae and A. ajax since this laminae in A. ajax
and A. excelsus passes under the diapophyses, not
touching the diapophysial-postzygapophysial laminae.
However when I looked at YPM 1980 (the original
"Brontosaurus") its cervicals contain this laminae,
but rather than raising to the top of the diapophyses
or passing underneath them, the laminae runs down the
backside of the diapophyses. An inbetween position.
This suggests, to me, that perhaps throughout the
animal's life these ridges of bone rise up along the
posterior of the cervicals. In A. louisae cervicals
3-4 have the raised ridge of bone, like in A.
excelsus.

* In A. excelsus, when its cervicals are looked at
from an anterior view you can see down the length of
the cervical (you can see under the prezygapophyses
and so on). In A. ajax and A. louisae there is lamina
that extends to each diapophysis, above this lamina is
a plate of bone that prevents you from seeing to the
back of the cervical. However in the later cervicals
of A. louisae, the bone above this lamina begins to
sink in (sinking into the cervical allowing you to see
further back). The lamina also raises up a bit
allowing you to see more. This could suggest that
these laminae and plates could gradually shrink
disappear throughout the animals' lives.


Deeming these traits as an invalid means of separating
A. excelsus from A. louisae I can only find one trait
remaining that could really separate the two species'
cervicals.

     In A. excelsus and A. louisae, two additional
cavities form above the posterior neural canal opening

in the mid-late cervicals (in the early cervicals the
two species the posterior neural canal opening sits
alone. In A. excelsus the two additional cavities are
present at first in the 7th cervical (MAYBE the 6th,
but it has not been found). In A. louisae these two
cavities first show up in cervical 8th.


YPM 1980 UNIQUE

     YPM 1980 stands alone as being different from the
U. of Wyoming A. excelsus, A. louisae, and A. ajax.

In all of the cervicals (except 1 and 2) of A.
louisae, and the U. of Wyoming A. excelsus, and
cervicals 9-10 and a non numbered cervical (only
figured cervicsld I have of A. ajax) contain two
cavities above their anterior neural canal opening.
However the figured cervical of YPM 1980 has no
cavities above its anterior neural canal opening.

This is where I stand in my analysis of Apatosaurus
cervicals (mainly A. louisae and A. excelsus
comparison at this point). 

In my opinion the whole genus of Apatosaurus needs to
be re-looked at. 

                                      -Michael Lima

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