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RE: Alamosaurus as biggest North American sauropod



  The best strategy, in my opinion, is to simply do away with crap taxa. If you 
base your nomen on crap, and you can't distinguish it from two or more taxa 
(MMM = Mickey Mortimer's metric), regardless of its provenance, horizon, or the 
authors' preclusions about its ontogeny or gender, then that nomen deserves to 
be relegated to the annals of me laughing at you (the nomen, not the 
descriptors). If MMM can be affirmed, then that taxon has little to fear. If 
not, however, then if there is another appropriate name that meets MMM, then 
that taxon shall be raised upon high, and the other dashed to the depths of 
ridicule.

  I prefer the use of type specimen comparison over any other process so far 
used to "assess" the _reasonableness_ of a "genus"'s validity, including but 
not limited to ontogeny, stratigraphic and geographic distribution. Morphologic 
comparison, placed first and foremost, assures us that degree of unique 
features can affirm characters distinguishing organisms. At this point, 
ontogeny can only inform, and stratigraphy and geography can only expand or 
reduce the range of the taxon, rather than provide real evidence to distinguish 
taxa in the absence of other data. The weight of the latter points can increase 
with age and distance, such as a ceratopsian from the Oldman Formation 
(Alberta, Canada) and one from the Judith River Formation (Montana, USA) 
[ignoring the Two Medicine Formation for the moment as it is effectively an 
extension of the JRF]; when the two are morphologically similar, enough so that 
features may be ontogenetically or individually variable when compared to the 
same range in other taxa, provenance and horizon are irrelevant. If, instead, 
they are >10ma apart, these features may be more qualifiable as distinct, 
regardless of the apparent similarities. Despite this, it would then be foolish 
of an author to then distinguish a new taxon for one when another has been 
proposed. In the event they are both established as new taxa, then they should 
both stand; otherwise, if either cannot be distinguished from at least two 
other taxa with which it might be referred, then that taxon should be relegated 
to the dust bin -- not subsumed, not transferred as a new subset of the 
"likelier" form, but simply discarded.

  In this respect, *Titanosaurus indicus* would show no unique features that 
can distinguish it from potential conspecifics, and encompasses a range of 
features present in the Lameta Formation. However, *Jainosaurus 
septentrionalis* can apparently be so distingushed, and though they may still 
be the same taxon, this cannot be _proven_. Based on the morphology-first 
principle of agreement (something I discussed here - 
http://qilong.wordpress.com/2011/01/28/splitting-chirostenotes/ - when 
concerned with this question in regards to *Chirostenotes pergracilis* and the 
awesomely large number of different _potential_ morphologies that have referred 
to it in the last 80 years), they cannot be referred to one another as neither 
shares the same morphology and characteristics. In this way, I would agree with 
Wilson & Upchurch's general conclusion that one should be raised, the other 
dropped.

  As it is somewhat common to note, the holotype of *Alamosaurus sanjuanensis* 
is apparently based on a juvenile, and it lacks distinctive characteristics 
permitting it's segregation from other particular titanosaurs. As the lack of 
reasonably complete material for the taxon exists, and that large sauropod 
skeletons are difficult to find in the latest Late Cretaceous of southern 
Laramidia, much less a degree of skeletal material that can be affirmed to 
belong to a single ontogenetic series of a single species, it is questionable 
to refer new material of a differential stage that cannot in itself be 
absolutely shown to bear distinguishing characteristics of the unique taxon, 
and that this taxon is the same as the type specimen of *Alamosaurus 
sanjuanensis*. The convention to retain use of this nomen, for appropriately 
historical reasons, is the same that makes *Titanosaurus indicus* rear is 
longish neck so frequently here: It is romantic to think that we can reduce the 
chaff and keep the first, most famous, historical names present. I disagree 
strongly the most when this convention is applied to tooth-based taxa (e.g., 
*Astrodon johnstoni* or *Revueltosaurus callenderi*) simply because tooth 
morphology should be expected to be under a constraint that departs from 
typical skeletal anatomy, and is both highly divergent in closely related 
species (e.g., the *Varanus* "genus" complex) or extremely similar despite high 
skeletal, ontogenetic and morphological disparity (e.g., *Canis lupus 
familiaris*). Greg Paul has used the latter two options and reasons to lump 
taxa, but I'd rather use them to tell people _not_ to lump taxa, and not to 
split them either.

Cheers,

  Jaime A. Headden
  The Bite Stuff (site v2)
  http://qilong.wordpress.com/

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)


"Ever since man first left his cave and met a stranger with a
different language and a new way of looking at things, the human race
has had a dream: to kill him, so we don't have to learn his language or
his new way of looking at things." --- Zapp Brannigan (Beast With a Billion 
Backs)


----------------------------------------
> Date: Fri, 9 Dec 2011 11:25:23 +1100
> From: tijawi@gmail.com
> To: dinosaur@usc.edu
> Subject: Re: Alamosaurus as biggest North American sauropod
>
> Matthew Martyniuk <martyniuk@gmail.com> wrote:
>
> > I don't see the issue with using parsimony. In fact I have kind of an
> > issue when people don't use it. If the remains can't be differentiated
> > from _A. sanjuanenis_, and there is no evidence to suggest multiple
> > taxa were present in this environment, it should be considered _A.
> > sanjuanenis_ until evidence to the contrary can be produced.
>
>
> As a rule of thumb, this "rule" is unevenly applied. For example,
> Carpenter and Tidwell (2004) referred all sauropod material from the
> Arundel Formation to a single taxon. All the Arundel sauropod
> material was consistent with the presence of a single species, which
> took the name _Astrodon johnsoni_. In the process, _Pleurocoelus
> nanus_ and _P. altus_ were considered to be subjective junior synonyms
> of _Astrodon johnsoni_, a taxon that was originally established on
> material that is not diagnostic at the genus level (tooth + tooth
> fragment).
>
>
> On the other hand, Wilson and Upchurch (2003) did *not* combine
> _Titanosaurus indicus_ and _Antarctosaurus septentrionalis_ into a
> single taxon in their revision of the titanosaur material from the
> 'Sauropod bed' of the Lameta Formation at Bara Simla. This was
> despite the fact that this study found no reason to recognize more
> than one species at Bara Simla. The Conclusion makes this clear:
>
>
> "The discussion above, however, demonstrates that
> Huene & Matley’s (1933) decision to separate the
> ‘Sauropod bed’ specimens into several individuals
> from two taxa is not supported by the available
> evidence. It is possible that only one individual was
> present, as originally suggested by Matley (1921).
> Even if more than one individual is represented,
> two or more taxa cannot yet be reliably distinguished.
> However, although morphological and geological data
> do not argue against the presence of a single species
> at Bara Simla, there is simply no positive evidence
> supporting this hypothesis."
>
>
> Because _T. indicus_ was based on material (two caudal vertebrae) that
> Wilson and Upchurch (2003) found to be non-diagnostic at the genus
> level, these authors declared _T. indicus_ to be a nomen dubium. _A.
> septentrionalis_ had been previously assigned its own genus
> (_Jainosaurus_; Hunt et al., 1994), which was the name adopted by
> later studies for the "valid" titanosaur from Bara Simla (e.g., Wilson
> et al., 2009, 2011 - the latter study assigned additional titanosaur
> material from a separate site [Chhota Simla] to _J. septentrionalis_
> ). However, I'm confused as to why all the titanosaur material from
> Bara Sima wasn't simply assigned to a single taxon that carried the
> name _T. indicus_, with _Jainosaurus septentrionalis_
> (=_Antarctosaurus septentrionalis_) as a junior synonym.
>
>
>
>
>
>
>
> Cheers
>
> Tim