Re: Bakker's Brontosaurus and Late Cretaceous populations

[Mike Taylor <mike@miketaylor.org.uk>]

> Date: Tue, 02 Aug 2005 12:00:12 -0500
> From: Tim Williams <twilliams_alpha@hotmail.com>
> 
> Like a lot of things, 'lumping' and 'splitting' are often in the eye
> of the beholder.  Nevertheless there are obvious examples of
> oversplitting.  In recent years there has been a tendency to
> consolidate.  The Morrison sauropods are a good example:
> _Cathetosaurus_, _Ultrasaurus_, _Supersaurus_, _Seismosaurus_ and
> maybe _Dystylosaurus_ have either already sunk or are about to be
> sunk into long-established genera.

Just to be picky --

_Cathetosaurus_ Jensen 1988 was indeed sunk into _Camarasaurus_ (as
the new species _C. lewisi_) by McIntosh et al. 1996, and this seems
to be generally accepted.  _Ultrasaurus_ Jensen 1985 (which was
renamed _Ultrasauros_ Olshevsky 1991 due to preoccupation by the nomen
dubium _Ultrasaurus_ Kim 1983) was emphatically sunk into
_Supersaurus_ Jensen 1985 by Curtice et al. 1996, and if you listen
carefully you can still hear the echoes of the >PLUNK< sound.  (If it
seems odd that the brachiosaur "Ultrasauros" should be sunk into a
diplodocid, that's because Jensen inexplicably nominated a dorsal as
the holotype of "U." instead of the indisputably brachiosaurid scapula
that is most associated with that name.)  And Curtice and Stadtman
(2001) further sunk _Dystylosaurus_ Jensen 1985 into _Supersaurus_,
reducing Jensen's bumper crop of three new giant sauropods to just
one.

The others you mentioned are less emphatic, though.  The only
published attempt to synonymising _Seismosaurus_ Gilette 1991 with
_Diplodocus_ (so far as I know) is Lucas and Heckert (2000); and all
they have to say is "previously misrepresented as [...] a new genus,
_Seismosaurus_, but clearly not distinct from Diplodocus (B. Curtice,
pers. comm., 2000)".  I'm not particularly convinced by a pers. comm.
for that, and apparently Gillette is readying a defence of
_Seismosaurus_, so I suspect we've not seen the last of Sam.

Finally, we come to the last of Jensen's beasts, _Supersaurus_.  The
closest shave it's had is in an abstract by Brian Curtice (2003),
which says "The former Dystylosaurus dorsal vertebra provides an
autapomorphy for Supersaurus, that being a strongly reduced bifid
neural spine on dorsal four.  This loss of bifidity is important for
in all other diplodocids the neural spine is still deeply bifurcated
on dorsal four.  Only Barosaurus has a reduction in cleft depth that
far forward in the dorsal column.  Supersaurus has all but lost the
cleft, more closely resembling the sixth dorsal vertebra of Barosaurus
than the fourth."  In other words, Curtice doesn't really commit
himself one way or the other; and his analysis has in any case now
been superseded by McIntosh's (2005) new _Barosaurus_ monograph, which
reaffirms the genus _Supersaurus_ as distinct from _B._

In conclusion, I think _Seismosaurus_ and (especially) _Supersaurus_
are good genera, although the other three you mention are indeed dead.
Hope that's helpful to someone out there.

 _/|_    ___________________________________________________________________
/o ) \/  Mike Taylor  <mike@miketaylor.org.uk>  http://www.miketaylor.org.uk
)_v__/\  "Life does not cease to be funny when people die, any more than
         it ceases to be serious when they laugh" -- George Bernard Shaw.


References
----------

Curtice, Brian D.  2003.  Two genera down, one to go?  The potential
synonomy[sic] of _Supersaurus_ with _Barosaurus_.  Southwest
Paleontological Symposium 2003, Guide to Presentations, Mesa Southwest
Museum, January 25 2003, unpaginated.

Curtice, Brian D. and Kenneth L. Stadtman.  2001.  The demise of
_Dystylosaurus edwini_ and a revision of _Supersaurus vivianae_.
Western Association of Vertebrate Paleontologists and Mesa Southwest
Museum and Southwest Paleontologists Symposium, Bulletin, 8,
pp. 33-40.

Curtice, Brian D., Kenneth L. Stadtman and Linda J. Curtice.  1996.  A
reassessment of Ultrasauros Macintoshi (Jensen, 1985).  The
continental Jurassic M. Morales (Ed.)  Museum of Northern Arizona
Bulletin. 60:87-95.

Gillette, D. D., 1991, Seismosaurus halli, gen. et sp. nov., a new
sauropod dinosaur from the Morrison Formation (Upper Jurassic/Lower
Cretaceous) of New Mexico, USA: Journal of Vertebrate Paleontology,
v. 11, n. 4, p.  417-433.

Jensen, J.A.  1985.  Three new sauropod dinosaurs from the Upper
Jurassic of Colorado.  Great Basin Naturalist 45(4):697-709.

Jensen, James A.  1988.  A fourth new sauropod dinosaur from the Upper
Jurassic of the Colorado Plateau and sauropod bipedalism.  Great Basin
Naturalist 48 (2): 121-145.

Kim, H. M. (1983). Cretaceous dinosaurs from
Korea. J. Geol. Soc. Korea 19:115-126.

Lucas, S. G. and A. B. Heckert.  2000.  Jurassic dinosaurs in New
Mexico; pp. 43-46 in S. G. Lucas and A. B. Heckert (eds.), Dinosaurs
of New Mexico.  Bulletin 17, New Mexico Museum of Natural History and
Science.

McIntosh, John S.  2005.  The Genus _Barosaurus_ Marsh (Sauropoda,
Diplodocidae).  pp. 38-77 in Virginia Tidwell and Ken Carpenter
(eds.), Thunder Lizards: the Sauropodomorph Dinosaurs.  Indiana
University Press, Bloomington, Indiana.  495 pp.

McIntosh, John S., Wade E. Miller, Kenneth L. Stadtman and David
D. Gillette.  1996.  The osteology of _Camarasaurus lewisi_ (Jensen,
1988).  BYU Geolgy Studies 41: 73-115.

Olshevsky, George.  1991.  A Revision of the Parainfraclass
Archosauria Cope, 1869, Excluding the Advanced Crocodylia.  Mesozoic
Meanderings #2 (1st printing): iv + 196 pp.