Re: Pleurocoelus question

[Tompaleo@aol.com]

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