Re: Morrison Sauropods\etc.

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

Justin Tweet wrote:

>         Of course, some are more distinctive than others.  Having all those
> super-diplodocids at the end of the Morrison is a bit suspicious
> (*Seismosaurus*, *Supersaurus*, the type of *Amphicoelias*...),

_Seismosaurus_ looks like it will be sunk into _Diplodocus_.  (This has been
published, though AFAIK the new combination _Diplodocus hallorum_ has yet to
officially come into existence).

_Supersaurus vivianae_ appears to be a valid genus and species, last I
heard.  It is quite distinctive from _Diplodocus_.

A new specimen of _Amphicoelias_ has bolstered the validity of this genus
(assuming the specimen is correctly referred).  John McIntosh is of the
opinion that _A. altus_ and (the super-large) _A. fragillimus_ be pooled
into a single _Amphicoelias_ species.

The status of other, more well-known (i.e. lots and lots of bones) Morrison
sauropod genera is in a state of flux.  Bakker has already split of
_Apatosaurus yahnahpin_ as a new genus (_Eobrontosaurus_).  Within
_Apatosaurtus_, it is becoming increasingly difficult to separate _A. ajax_
from _A. excelsus_ (type of _Brontosaurus_); McIntosh used size alone to
distinguish the two.  _A. ajax_ has a larger adult body size; but there's
some pretty big _A. excelsus_ stuff around (referred to _A. excelsus_, I
believe, on stratigraphical grounds).  The rarer _A. louisae_ seems a happy
species though.

Apparently there is a new sauropod skull floating about, which Bakker has
suggested may belong to _A. excelsus_ (thereby justify the resurrection of
_Brontosaurus_).  Mine is not to reason why.

Distinguishing _Diplodocus longi_ from _D. carnegii_ is also very tricky.
_D. hayi_ looks good.

Regarding _Camarasaurus_, the distinction between _C. grandis_ and _C.
supremus_ faces the same trouble as _A. excelsus_ vs _A. ajax_: Does size
matter?

I happen to think _Cathetosaurus_ is a valid genus, though of late it is
more usually sunk into the genus _Camarasaurus_ as _Camarasaurus lewisi_.
The
anterodorsal rotation of the ilium seen in _C. lewisi_ might very well be a
derived feature which it shares with the Titanosauriformes rather than an
autapomorphy for the species _C. lewisi_.


Hope this helps.


Tim

------------------------------------------------------------

Timothy J. Williams

USDA/ARS Researcher
Agronomy Hall
Iowa State University
Ames IA 50014

Phone: 515 294 9233
Fax:   515 294 3163

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