Re: Pleurocoelus question

["Steve Brusatte" <dinoland@lycos.com>]

On Tue, 12 Jun 2001 23:47:37  
 Tompaleo wrote:
>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 ;-)

Oh, yeah, I'm just getting started.  That's why I turned to all of you experts 
on the list :-))  I just wish that there were some dinosaur-bearing deposits in 
Illinois.  I'll just have to stick to brachiopods for awhile, I guess.  

>>  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.  

I do realize that its general shape is still peg-like.  However, I agree with 
Ray.  Somebody should try to conduct a study on the cross section of these 
sauropod teeth, at least in brachiosaurids, and see how prevalent this star 
shape is.  Like Ray, I also don't doubt the fact that the star shape may be 
widespread, but we'll never known until somebody does some research.  

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. 

That's interesting.  If you find some time and don't mind "destroying" 
perfectly fine specimens, cut a few of them up and examine them under a 
microscope!
>
>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.

I haven't seen the specimens, but I have seen pictures.  Pleurocoelus is a 
small sauropod, which is where some of the confusion may have stemmed from.  
>
>Conclusion: All sauropod material from the Arundel should now be referred to 
>Pleurocoelus, and _P._altus_ at that - the more valid nomen.

This may very well be true, and would make sense.  But, I still abide by my 
first post, and think that some sort of study should be done.  If somebody 
shows me evidence that Pleurocoelus, and other brachiosaurids, have these 
star-shaped cross sections, I will then forget about Astrodon!
>
>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!

You may very well be right, but show me the papers!  Honestly, I think that 
Pleurocoelus and Astrodon are poor choices for state fossils, especially 
Pleurocoelus.  Texas would have been much better off designating Brontopodus, 
or maybe Eryops.  

Steve


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