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RE: Alamosaurus as biggest North American sauropod



  My best example would actually be what is now recognized as *Revueltosaurus 
callenderi*. Originally a single tooth morphology. Later found to correspond to 
a heterodont taxon. Material now shows that the premaxillary, anterior dentary 
and posterior dentary/all maxillary teeth correspond to morphologies occuring 
in other isolated toothed taxa, such as *Galtonia gibbidens* and *Pekinosaurus 
olseni*. This material may represent crurotarsan dentition, and may come from 
highly similar animals; indeed, Irmis et al. (2007) referred both to as 
*Revueltosaurus* sp.. It is significant enough that one can raise doubt as to 
the "reasonableness" of the referral of the isolated teeth that form the 
original material to _any_ skeletal material with similar teeth, barring 
extraordinary luck in finding the appropriate jaw bones next to the original 
shed crowns. I have discussed this issue with tooth guys, and they are aware of 
the problem, but note that these referrals are supplemented by the addition of 
geographic and stratigraphic constraints, which narrow the possible owners.

  Despite this, even species may differ without significant (or any) dental 
change, and this is a caution that should have been applied. That heterodonty 
is present not just in ornithischians but in crurotarsans such as 
"revueltosaurs," as well as silesaurids, including a typically "ornithischian" 
aspect to the teeth, that one cannot show or demonstrate that these 
morphologies are not consistent in a single animal. This should raise the 
specter of doubt when it comes to the question "Should I name this taxon?" My 
argument is that the answer should be "No," but the adventurous taxonomist will 
say "Yes." In keeping with my argument and extending it to this level of 
egoism, I'd like to note that good things can come of it, but this hardly 
outweighs the problems: an author publishes more papers, increasing his 
notoriety and allows his work to speak volume simply because it is larger, he 
has named many taxa, and even has taxa named for himself. If taxonomy were a 
business, some nomenclators would be rich.

Irmis, R. B., Parker, W. G., Nesbitt, S. J. & Liu J. 2007. Early ornithischian 
dinosaurs: The Triassic record. _Historical Biology_ 19(1):3-22.

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)


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> Date: Fri, 9 Dec 2011 17:54:02 -0300
> Subject: Re: Alamosaurus as biggest North American sauropod
> From: augustoharo@gmail.com
> To: qi_leong@hotmail.com
> CC: martyniuk@gmail.com; Dinosaur.Mailing.List@listproc.usc.edu
>
> 2011/12/9 Jaime Headden <qi_leong@hotmail.com>:
> >
> >   As collection and investigation proceeds, we should eventually begin to 
> > collect more and more of potentially new taxa. If we relegate our choices 
> > for what gets named to reasonably complete specimens and groups of such 
> > specimens, regardless of the fact that "the fossil record is incomplete!!", 
> > then the taxonomy is likelier to become more stable, not less. If naming 
> > conventions based on single elements, or bunches of scrap, as was the case 
> > with *Allosaurus fragilis* or such, persist, then the problem of crap 
> > material (and thus crap taxa) continues.
> >
> What would be the problem with a "crap" taxon identified by a tooth? I
> would guess if you just find that many taxa later described shared the
> same features of the tooth, you simply drop the taxon and then regard
> the material upon which it was erected as indeterminate. The taxon can
> die, but as long as no more than one taxon was recognized with that
> tooth morphology, the name at least served to refer to that morphology
> (this makes sense to me because I think in practice, names are better
> descriptors of morphotypes than they are of such an ambiguous concept
> as "species", overall, but not only, in paleontology). So taxonomy
> would be more stable, yes, but we would be left with less labels to
> refer to morphotypes, which in my opinion would be a drawback
> regarding communication.
> Besides, how much complete a skeleton has to be to erect a name, seems
> arbitrary (for a skeleton which is 80% complete may still leave the
> doubt that two taxa can show significant differences in the unknown
> 20%; in addition, the entire skeleton per se is a very small part of
> the entire anatomical information of an animal).