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Re: Astrodon vs Pleurocoelous



With all due respect to Tim and to Salgado et al.?
> 
>  If Salgado and co are correct, no less than THREE sauropod genera are 
>  represented from among the Lower Cretaceous North American material 
>  traditionally named "Pleurocoelus".  According to recent research (which 
is 
>  still in progress)...
  
This was first posited by Marsh (1888). I'm not sure what paper Tim is 
referring to so I cannot comment on it at this time. However, almost no one 
on this side of the pond, including myself believes there are two taxa let 
alone one taxon of Pleurocoelus present in Maryland. The referred specimens 
_are_ most likely juvenile or sub-adult and adult forms of the same sauropod. 
 Since the only known sauropod teeth found in the Arundel are those of 
_Astrodon_johnstoni_ (Leidy, 1865) and _predates Marsh, it stands to reason 
they all belong to the same beast and most of us who work on Arundel material 
refer all to A. johnstoni. Furthermore, most of the skeletal remains came 
from the very same locality as did the teeth.
Marsh (1888, 1896), erroneously believed that sauropods were  Jurassic in age 
based on his work out west.  Thus he believed the Potomac Fm. or at least the 
part containing the Arundel Clay was late Jurassic. (See also my paper, Lipka 
, 1998 for a brief discussion of this on the web at: 
http://www.wam.umd.edu/~lfsxdth/dino/lipka/theropod.html)


>  (1) _Pleurocoelus nanus_ (type species, from the Arundel Formation of
>  Maryland) is a brachiosaurid (or at least outside the Titanosauria); it 
>  shows a few titanosauriform synapomorphs (absence of phalangeal articular 
>  surfaces on the distal metacarpals; transversely expanded distal tibia), 
but 
 
Probably so. The concessus, based on the available material seems to lean 
towards  _Brachiosaurid_


>>  (3) The _Pleurocoelus_ material from the Comanche Series of Texas,
>  definitely does NOT belong in the genus _Pleurocoelus_.  Its anterior
>  caudals are weakly procoelous.  Based on this and other features, the 
>  Comanche sauropod may be a basal titanosaur, and possibly the same as 
>  _Cedarosaurus_.
  
For this I refer you to Matt Wedel's et al., (2000) JVP (V. 20 no. 1) paper, 
111;
"The customary assignment of any sauropod remains from the Aptian-Albian of 
North America to the genus _Pleurocoelus_ should be reexamined in light of 
the dsicovery of _Sauroposeidon_

Thus "Pleurocoelus" sp. is pushed further west than Oklahoma!

Indeed, I was privileged to see the cervical series of _Sauropoeseidon_  a 
couple years ago when it was still a "Pleurocoelus". It was of course still 
in matrix. It is huge for an Aptian-Albian sauropod and evidently larger than 
even "P. altus". The Antlers Fm. of Oklahoma  also _does_ have Astrodon-like 
(damn near identical to my Arundel specimens!) teeth.  However all the OMNH 
specimens I have seen are small compared to the often larger  Arundel 
specimens but the range in sizes between teeth from these two sites do 
overlap. There are similar teeth in the Cloverly Fm (Units V-VII)  as well.

The point(s) I want to emphasize regarding the Arundel sauropods that at 
present, "Pleurocoelus sp." of any kind are not generally regarded to occur 
in the Arundel. The preferred taxon for the Maryland sauropod is in fact 
_Astrodon_johnstoni_.  It is likely a brachiosaurid. It is clear from fossil 
evidence from units _contemporaneous_  with the Arundel Clay (early -- mid 
Aptian) that several distinct genera of medium to large sauropods  were still 
roaming around North America well after the end Jurassic "extinction" of 
sauropods in general in N. America.

Select Bibliography:

Lipka, T., R., 1996, Recovery of new dinosaur and other fossils from the 
Early Cretaceous Arundel Clay Facies (Potomac Group) of the central Maryland, 
USA in Babcock, L. E. and Ausich, W. I. (eds.), Sixth North American  
Paleontological Convention  Abstracts of Papers, The Paleontological Society, 
Special Publication 8, p. 241. 

Lipka, T. R., 1998, The affinities of the enigmatic theropods of the Arundel 
Clay facies (Aptian), Potomac Formation, Atlantic Coastal Plain of Maryland 
in Lucas, S. G., Kirkland, J. I., and Estep, J. (eds.), Lower and Middle 
Cretaceous terrestrial ecosystems, New Mexico Museum of Natural History 
Bulletin 14, p. 229-234    

Lull, R. S., 1911a , The Fauna of the Arundel Formation, Lower Cretaceous 
Formations of the United States, Maryland Geological Survey, Lower Cretaceous 
Volume p. 173-178. 

Lull, R. S., 1911 b, Systematic paleontology of the Lower Cretaceous deposits 
of Maryland: Vertebrate. Lower Cretaceous Volume, Maryland Geological Survey 
, p. 183-211.

Marsh, O. C., 1888, Notice of a new genus of Sauropoda and other dinosaurs 
from the Potomac Formation, American Journal of Science,  3rd Series, v. 35, 
p. 89-94
  
               ----, 1896,  The Jurassic formations in the Atlantic coast, 
American Journal of Science, Fourth Series, v. II, p. 433-447. 

Ostrom, J. H., 1970, Stratigraphy and paleontology of the Cloverly Formation 
(Lower Cretaceous) of the Bighorn Basin area, Wyoming and Montana, Yale 
Peabody Museum Bulletin 35, 234 p.

Wedel, M. J., Cifelli, R.L., and Sanders, R.K., 2000. Sauroposeidon proteles, 
a new sauropod from the early Cretaceous of Oklahoma. JVP, v. 20 no. 1, p. 
109-114

Hope this helps!

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