Re: Astrodon vs Pleurocoelous

["Timothy Williams" <twilliams_alpha@hotmail.com>]

Thomas R. Lipka wrote:

> 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.


The abstract (no paper AFAIK) is from 
http://blackwidow.informatics.sunysb.edu/anatsci/browse.cfm
where you can find lots of other goodies.

PHYLOGENETIC RELATIONSHIPS OF Pleurocoelus Marsh (SAUROPODA)?

Leonardo Salgado and Jorge Calvo, Museo de Ciencias Naturales, Universidad 
Nacional del Comahue,  Buenos Aires 140, (8300) Neuquén, Argentina Rodolfo 
A. Coria, Museo "Carmen Funes" Subsecretaria de Cultura de Neuquén, (8318) 
Plaza Huincul, Neuquén, Argentina

(translated by:
Jeffrey A. Wilson
University of Chicago
Department of Organismal Biology & Anatomy
July 1997)

	The genus Pleurocoelus was originally proposed by Marsh to include material 
from the Arundel Formation (Lower Cretaceous) of Maryland, United States.  
Marsh recognized two species, P. nanus and P. altus.  The former is well 
represented by a collection of mostly disarticulated elements, while the 
latter is known from only a tibia and some isolated vertebrae.  Moreover, 
the presence of the genus Pleurocoelus was mentioned in Middle Cretaceous 
strata in the central north and central west of Texas (Comanche Series, 
Trinity Group).  A reinterpretation of material previously assigned to 
Pleurocoelus suggests that (1) P. nanus corresponds to a valid species; (2) 
P. altus does not appear to correspond to an adult of P. nanus, as was 
proposed be various authors; and (3) sufficient evidence does not exist to 
demonstrate that the Comanchean species and the Maryland species correspond 
to the same genus (Pleurocoelus).
	Pleurocoelus was traditionally included in the family Brachiosauridae, 
extending the biochron of this family of sauropods.  In a numerical analysis 
of characters considered from the material previously assigned to 
Pleurocoelus, P. nanus is found to be the sister group to titanosaurs.  
These taxa share, among others, the following characters: absence of 
phalangeal articular surfaces on the distal metacarpals, and a transversely 
expanded distal tibia.  Pleurocoelus retains anterior caudal vertebrae with 
flattened articular faces.  "Pleurocoelus" altus exhibits an 
anteroposteriorly expanded distal tibia, a character which is plesiomorphic 
for sauropods.
	The species represented in the Comanchean are probably basal members of the 
Titanosauria , as they present slightly procoelous anterior caudal 
vertebrae, dorsal vertebrae with the infradiapophyseal laminae bifurcated at 
their base, and the presence of a centro-parapophyseal lamina.  Ichnological 
evidence supports the existence of basal titanosaurs in North America during 
the Middle Cretaceous.


>  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.

If all the Arundel sauropod skeletal material (_P. nanus_ & _P. altus_) does 
indeed belong to a single species, then it makes sense to assume that the 
sauropod teeth (_Astrodon johnstoni_) also belong to this species, and to 
call that species _Astrodon johnstoni_.  But if there is some doubt on this 
issue (as raised by Salgado et al.: "P. altus does not appear to correspond 
to an adult of P. nanus, as was proposed be various authors"), then the 
tooth taxon _A. johnstoni_ cannot be combined with either skeletal-based 
taxon from Arundel.


> "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_.

I think on this point we are in complete agreement.  The referral of any 
non-Arundel material to _Pleurocoelus_ should be reconsidered.  The 
"Pleurocoelus" material from Oklahoma is now _Sauroposeidon_, and the 
Comanche "Pleurocoelus" material (AFAIK) certainly belongs elsewhere 
(related to _Cedarosaurus_?).   The implication of Salgado et al's work is 
that _Pleurocoelus_ should be limited to the type species (_P. nanus_).


> 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.

I'm a little confused here.  The type material for _Pleurocoelus_ is from 
Arundel.  True, certain Early Cretaceous sauropod material from North 
America has been referred to this genus (as "Pleurocoelus" sp.). But I think 
we can be reasonably certain that this material does not belong in the same 
genus as the type _Pleurocoelus_ species (which, if there is indeed one 
sauropod species from Arundel, can be referred to _Astrodon_.  If not...).

Thanks for the info!

Cheers

Tim
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