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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
> 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:
> (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),
Probably so. The concessus, based on the available material seems to lean
>> (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
For this I refer you to Matt Wedel's et al., (2000) JVP (V. 20 no. 1) paper,
"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.
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,
----, 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.
Hope this helps!
Thomas R. Lipka