[toni.naish@btinternet.com: Alamosaurus a nomen dubium?]

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

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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Envelope-to: mike@miketaylor.org.uk
Delivery-date: Fri, 15 Jul 2005 18:59:52 +0200
From: "Toni" <toni.naish@btinternet.com>
To: "Mike Taylor" <mike@miketaylor.org.uk>
Cc: "darren uni" <darren.naish@port.ac.uk>
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!
 ribs
 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 
holotyp!
e. Given
 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, 
864-869.

 

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.


- -- 
Darren Naish
School of Earth & Environmental Sciences
Burnaby Building, Burnaby Rd
University of Portsmouth 
Portsmouth, UK, PO1 3QL

email: darren.naish@port.ac.uk
[send large attachments to: eotyrannus@gmail.com]
tel: 023 92846045





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