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[firstname.lastname@example.org: Alamosaurus a nomen dubium?]
As Darren's self-imposed thesis deadline approaches, so his rate of
generating absurdly erudite mini-dissertations on groups he's not
supposed to be particularly knowledgeable about but inexplicably is,
tends asymptotically to infinity. Stand by: some time in the next
eight minutes, I expect to forward a message outlining a definitive
new phylogeny of temnospondyls. Meanwhile, enjoy this one.
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Delivery-date: Fri, 15 Jul 2005 18:59:52 +0200
From: "Toni" <email@example.com>
To: "Mike Taylor" <firstname.lastname@example.org>
Cc: "darren uni" <email@example.com>
Subject: Alamosaurus a nomen dubium?
Date: Fri, 15 Jul 2005 18:08:35 +0100
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Me AGAIN. Will reply to your personal email(s) tonight. Meanwhile, could you
AGAIN fwd this to DML for me please? It wasn't easy to write this while looking
after a 3 yr old, and as for the thesis....
WRT Denver Fowler's assertion (hi Denver) that _Alamosaurus sanjuanensis_
should be considered a nomen dubium because Gilmore's 1922 type material (the
scapula USNM 10486) is non-diagnostic - and speaking of course as someone who
has pretty much made a career out of describing isolated limb bones and
vertebrae - we should not be so hasty in relegating this taxon to the dustbin.
Fair enough; (1) the paratype ischium described by Gilmore was found 60 m from
the holotype, was regarded by Gilmore as belonging to a second individual, and
could conceivably belong to a different taxon; (2) the topotype material
described by Mateer (1976), Kues et al. (1980) and others is also not
demonstrably conspecific with either the holotype or paratype; (3)
_Alamosaurus_ has clearly become a 'form genus' (Sullivan & Lucas 2000, p. 400)
to which all manner of Campanian and Maastrichtian titanosaur bits and pieces
have been referred.
However, the paratype ischium (USNM 10487) is 'nearly identical' (Lehman &
Coulson 2002, p. 164) to that of the good referred skeleton TMM 43621-1. This
is significant because, as you can see from fig. 9 in Lehman & Coulson (2002)
[where the word 'ilium' is accidentally used instead of 'ischium' in the figure
caption], titanosaur ischia differ enough in the dorsoventral depth and
orientation of the pubic peduncle and other features to be diagnostic. Hence
USNM 10487 and the juvenile specimen from Big Bend National Park (TMM 43621-1)
can be confidently regarded as the same taxon. This is great because, given
that there's no reason to think that 43621-1 represents more than one
individual, we now have associated cervical and dorsal vertebrae, coracoid,
humerus, ulna, pelvis, tibia, fibula and a metatarsal (Lehman & Coulson 2002).
If we now compare the many other elements referred to _A. sanjuanensis_ with
TMM 43621-1 we find that some, again, are identical, and hence should be
regarded as belonging to the same taxon as Gilmore's paratype ischium. And,
importantly, among these are the humerus, ulna, coracoid and ischium of USNM
15560: this is the associated North Horn Formation skeleton described by
Gilmore (1946). This specimen is perhaps, historically, the most important
specimen here because it also includes a nearly complete tail and both sternal
plates, and it's characters in these elements that have most often been used as
diagnostic for _A. sanjuanensis_. Wilson (2002) cited as diagnostic for this
taxon 'anterior and middle caudal vertebrae with several foramina opening at
base of transverse process, posterior caudal vertebrae with notched ventral
margins on anterior and posterior centrum faces, ulnar shaft not stout
[reversal]' (p. 275), while Upchurch et al. (2004) wrote of 'absence of caudal!
from caudal vertebra 9 onward [sic] and an acute rather than broad
craniolateral process of the sternal plate' (p. 311): both Wilson and Upchurch
et al. clearly used USNM 15560 when formulated their diagnoses.
However, at least some referred specimens differ from TMM 43621-1 (e.g. the
dorsal verts TMM 41398-1 and 41541-1, which sport lateral flanges on their
neural spines not seen in 43621-1), so could perhaps indicate different taxa..
but, then again, 43621-1 is a juvenile, so ontogeny rears its ugly head.
Two good, associated skeletons - whose material overlaps with each other, and
with Gilmore's paratype ischium - therefore show that there >is< a valid
Campanian-Maastrichtian North American lithostrotian, for which the name
_Alamosaurus sanjuanensis_ has historically been associated. But, given that
none of this overlaps with the non-diagnostic holotype.. is this lithostrotian
really _A. sanjuanensis_? On this I agree with Lucas & Sullivan (2000) who
wrote 'Certainly one, and possible more, titanosaurid taxa are represented by
the thus-far collected specimens of _Alamosaurus_, but the name _A.
sanjuanensis_ is based on an inadequate holotype. If and when a potentially
diagnostic specimen is discovered, we believe it will be useful (by preserving
longstanding usage) to set aside the holotype and designate a neotype' (p.
150). In their otherwise excellent paper, Lehman & Coulson (2002) didn't
comment on this problem, and hence _A. sanjuanensis_ remains based on a dodgy
the above I feel it would be easy to sort this out and fix _A. sanjuanensis_
as a clearly valid, diagnosable taxon. There is a publication in this I suppose.
Re: the size of _A. sanjuanensis_ (or, at least, of the same taxon as that
represented by the paratype and 43621-1), Lehman & Coulson (2002, p. 169)
estimated a considerable adult size (I won't attempt to estimate it from their
fig. 11, given my track record with mathematics) and wrote of _A. sanjuanensis_
as 'among the largest of sauropod dinosaurs'.
Finally, regarding changing views on sauropod biology, it is not correct to say
that people regarded sauropods as terrestrial until the 1920s and 30s. Ok:
Phillips, Mantell, Marsh, Cope and others suggested terrestrial habits for
sauropods on numerous occasions in the 1800s, but in general quite the opposite
is true. Of course Owen, in describing _Cetiosaurus_ in 1841-2, regarded it as
a giant aquatic crocodilian. When sauropods became dinosaurs this view was
transferred across, and later endorsed by Marsh and Cope's discovery of
retracted external nostrils and supposedly weak teeth. Marsh and Cope came to
regard sauropods as amphibious by the 1880s at least, and by now everyone was
simply assuming that this must have been right. Riggs deserves a lot of credit
for interpreting sauropods 'correctly' as early as 1904, but otherwise
sauropods stayed where Owen put them right up into the 1970s. I feel (this
point is rarely emphasised enough) that the most important factor in the
amphibious/aquatic sauropod myth was therefore historical contingency: Owen
made the initial mistake, but even as views on these animals changed, his
interpretation of their lifestyle was not properly questioned or rejected. By
analogy, the giant predatory bird _Phorusrhacos_ is ALWAYS (pretty much)
restored with black and white plumage. Why? Well, because that's how it was
first depicted by Zdenek Burian! Ah, the burden of history.
Refs - -
Gilmore, C. W. 1922. A new sauropod dinosaur from the Ojo Alamo Formation of
New Mexico. _Smithsonian Miscelleneous Collection_ 72, 1-9.
- - . 1946. Reptilian fauna from the North Horn Formation of central Utah. _U.
S. Geological Survey Professional Paper_ 210-C, 29-52.
Lehman, T. M. & Coulson, A. B. 2002. A juvenile specimen of the sauropod
dinosaur Alamosaurus sanjuanensis from the Upper Cretaceous of Big Bend
National Park, Texas. _Journal of Paleontology_ 76, 156-172.
Lucas, S. G. & Sullivan, R. M. 2000. The sauropod dinosaur Alamosaurus from the
Upper Cretaceous of the San Juan Basin, New Mexico. _New Mexico Museum of
Natural History and Science Bulletin_ 17, 147-156.
Kues, B. S., Lehman, T. & Rigby, J. K. 1980. The teeth of _Alamosaurus
sanjuanensis_, a Late Cretaceous sauropods. _Journal of Paleontology_ 54,
Mateer, N. J. 1976. New topotypes of _Alamosaurus sanjuanensis_ Gilmore
(Reptilia: Sauropoda). _Bulletin of the Geological Institutions of the
University of Uppsala, New Series_ 6, 93-95.
Sullivan, R. M. & Lucas, S. G. 2000. _Alamosaurus_ (Dinosauria: Sauropoda) from
the late Campanian of New Mexico and its significance. _Journal of Vertebrate
Paleontology_ 20, 400-403.
Upchurch, P., Barrett, P. M. & Dodson, P. 2004. Sauropoda. In Weishampel, D.
B., Dodson, P. & Osmólska, H. (eds) _The Dinosauria_. University of California
Press (Berkeley), pp. 259-322.
Wilson, J. A. 2002. Sauropod dinosaur phylogeny: critique and cladistic
analysis. _Zoological Journal of the Linnean Society_ 136, 217-276.
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