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Re: Pleurocoelus question



    First, I want to express appreciation to each person who has contributed
to out discussion of the Pleurocoelus/Astrodon controversy. Personally, I am
pretty well convinced that the Texas sauropod(s?) that have been called
Pleurocoelus are in fact a different species(s) than the Maryland
sauropod(s?).  Although it may not be relevant, quite a few of the sauropod
tracks I have found here in Maryland look in consistent ways sufficiently
different from the Glen Rose sauropod tracks with which many of us are
familiar, that it gives me at least a suspicion that the Maryland sauropod
track-maker(s) could have been different from the type making the famous
Texas tracks -- and I say this while trying to taking substrate type and
consistent form across various local substrate types into consideration.

    Thanks, Tom Lipka for pointing to the external similarities of many
sauropod teeth based on your extensive experience in finding and handling
Maryland sauropod teeth and comparing their external form with those of
sauropods from elsewhere. But, now, because Astrodon johnstoni was based (as
Steve pointed out) upon a tooth with a star-shaped pulp section, it seems to
me someone with access to the teeth of a lot of sauropods should take a look
at the pulp cross-section (and not just their external similarities) of some
of those other sauropod teeth from Texas (if they exist) and elsewhere and
see whether they have the star shaped pulp cross-section.

    If I were betting on the matter, I would take pretty large odds that the
star-shaped section is NOT unique to the Maryland sauropods (even as their
external form is not unique), but feel that comparing it to the
cross-section of sauropod teeth from elsewhere (including Texas, if they are
available) would be a worthwhile undertaking that could settle the matter of
whether the Maryland sauropod(s) are different in that particular respect.
So far as I know, no one has done that, but Tom may know more certainly
about it.  If -- and that's a big if -- the pulp shaped cross-section of the
Maryland sauropod tooth should prove unique when compared to those from
elsewhere, then it seems to me that the person who makes that examination
would have a find of substantial importance and a feather in his or her
scientific hat (to use a figure of speech).

    Tom?  Others?  Any takers?

    Ray Stanford


----- Original Message -----
From: <Tompaleo@aol.com>
To: <dinosaur@usc.edu>
Sent: Tuesday, June 12, 2001 11:47 PM
Subject: Re: Pleurocoelus question


In a message dated 6/12/01 9:00:51 PM Eastern Daylight Time,
dinoland@lycos.com writes:

>
>  Okay, fine, but who is to say that Astrodon is a nomen dubium.  I was
just
> talking about this with Ray Stanford off list (feel free to jump in, Ray
:-).
>  I've done a lot of reading on the early discoveries of this dinosaur for
a
> project during the past week or so.

So have I and many others, both on and off this list,  and over a
considerably longer time ;-)


 From what I have read, the first
> Astrodon specimens were discovered by a chemist, who showed the specimens
(a
> few teeth) to a dentist.  This dentist, Christopher Johnson, named the
tooth,
> diagnosing it as having a "star shape" when cross cut.  Leidy officially
> named the species and described it in 1865, keeping Johnson's diagnosis.

Right. Good research!


>  To me, the species is diagnostic, unless tooth evidence does not count...
>  >

BINGO! In the case of sauropods, it does not! Sauropod teeth in general are
not distinct enough for taxonomic distinction. The  "Astrodon" form is a
general form expressed by other genera not necessarily related to it. Though
star shaped in x-section, it is still a peg like  in overall shape which
might indicate basal titanosaur or brachiosaur.  Matt Wedel refers to the
"Astrodon" morph as a "form genus" . I can see why, I have also seen and
recovered these _exact_ shaped_teeth from the Antlers Fm. of Oklahoma (home
of _Sauroposeidon_) and in the Cloverly Fm. of MT (along with a considerable
number of postcrania and verrts of a yet to be described sauropod that are
NOT pleurocoelus sensu Pleurocoelus sp.) If the teeth from these localities
were mixed in with my Arundel material, it would be impossible to
distinguish
them! But it is a  near certainty that they belong to entirely different
genera.

Additionally, regarding the Maryland taxon, _P. altus _ (Marsh) was named
for
the material belonging to a larger (ie. more adult)  sauropod than that
which
belonged to the smaller  (more juvenile)_P. nanus_. Virtually all who have
seen the material, including myself,  recognize the likelhood that the two
represent ontogenetic variants on the same Pleurocoelus  sp.(?) theme. Alas,
the teeth we now refer to as  Astrodon, likely belonged to Pleurocoelus
(likely _altus__ ) INMHO.

Conclusion: All sauropod material from the Arundel should now be referred to
Pleurocoelus, and _P._altus_ at that - the more valid nomen.

And just because Leidy named it just doesn't make it so!  Ditto for O. C.
Marsh. Where the Arundel is concerned, Marsh's nomenclature leaves much to
be
desired!  I am having a ball with his theropoda! ;-)
He even believed the Arundel to be of Jurassic age because of the presence
of
this sauropod. The Arundel is firmly dated to late-early K (Aptian) age.
And,
we all now know that sauropods survived into the Late-K.

At least Marsh gave us a framework from which to build upon.

Finally, all of the above represents a turn around in my thinking regarding
Astrodon. I used to regard the "Astrodon" problem much the same way you do
now  Steve. But with recent discoveries, and work by Salgado, Wedel and
others, and my own pers. obs.,  I have seen the light. My "Maryland Pride"
has been humbled!

Well, it's past my bedtime so I'll close before I really step on a mine!

Cheers,

Tom

Thomas R. Lipka
Paleontological/Geological Studies
Tompaleo@aol.com