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RE: Andrew McDonald response re: European iguanodonts



  Understand that the provenances for proposed neotypes should, if at all 
possible, derive from the same formation as the holotype. This occurs with 
regard to Carrano et al.'s propoal for a neotype of *Majungasaurus 
crenatissimus,* using Lavocát's material over Depéret & Savornin's holotype 
(presumably to avoid using Sues & Galton's *Majungatholus atopus*). I mention 
this (with citations) here: 
http://qilong.wordpress.com/2011/03/11/systematic-originalism/ . Both taxa 
occur in the Maeverano Formation, and may have been collected close to one 
another in similar levels of the formation.

  The situation is similar to *Titanosaurus indicus*, where the holotype of 
*Titanosaurus colberti* (read: *Isisaurus*)  comes from the same hill and 
formation as the type species/specimen, but eas excluded merely for purposes of 
implied poor stability on the part of *Titanosaurus indicus* and slight 
variation in the preserved caudals (ignoring variation in the holotype and 
paratype caudals of the rejected taxon). We could reasonably state that 
*Isisaurus colberti* is a junior synonym of *Titanosaurus indicus* by 
designating the holotype of the former as the neotype of the latter. This 
situation would be similar to what was done for *Coelophysis bauri*, despite 
being rather different. In that case, specimens from a different formation 
entirely, of a different stratigraphic position (only slightly different), of a 
different locality, made the basis of new taxonomy (*Rioarribasaurus 
colberti*), in favor of nomenclature that was older, the basis of further 
employed taxonomy (*Coelophysidae,* *Coleophysoidea,* etc.), and more 
recognizable.

  Greater issues are present when it comes to *Troodon formosus* of the Judith 
River Formation of Montana, from which body fossils of troodontids are unknown 
but which exist in laterally continguous Two Medicine Formation beds and in 
less laterally contiguous but of likely same-age Dinosaur Park Formation. Here, 
a person can make a geographic argument that body fossils and the variation 
that exists among dentition leads to doubt about taxonomic overlap, especially 
as there are very few teeth that are _identical_ in morphology and size to the 
holotype (this is a "taste" issue, though -- I am overly picky on this point, 
but I have a particular reason). The best options (in my opinion) for a neotype 
would be material from the Two Medicine, which have failed to be published on 
for nearly two decades, but I would think a more or less complete cranial 
sample would be best. Otherwise, cranial material referred to *Stenonychosaurus 
inequalis* from the RTMP of Dinosaur Park Formation (Currie, 1987) is the best 
non-dental-bearing cranial material found so far, and would also be useful. I 
do not think any of this material _should_ bear the name, though, and we should 
simply stop using the name for the material from Alberta, Montana, Wyoming, and 
Alaska formations, aside from the type tooth.

  Note that some taxa for which neotypes seem preferable are problematic: 
*Spinosaurus aegyptiacus* is known (apparently) from material from Algeria, 
Tunisia, and Morocco, but good cranial or spinal material does not come from 
Egypt, and the Kem Kem and other formations are not in the same stratigraphic 
level as the Baharija. The same is true of *Carcharodontosaurus saharicus,* 
which while known for the skull from Morocco, is based on teeth from Algeria 
(?Albian) -- the possible neotype material comes from younger sediments 
(Cenomanian). Such temporal distance can be used as a proxy for taxonomic 
distance, at least in well-sampled and broad ranging sediments such as Dinosaur 
Park Formation and Hell Creek Formation, so why then should this not be true 
elsewhere? It is, in fact, the reason I don't think the neotype of *Coelophysis 
bauri* was properly selected: Padian's 1986 specimen _should_ have been better, 
being a whole specimen and from the type locality and formation. The same 
should then be true of other taxa. That we do not have good material from type 
formations is irrelevant, and the nomenclature may simply be set aside _until 
then_.

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: Mon, 4 Apr 2011 10:37:50 +1000
> From: tijawi@gmail.com
> To: dinosaur@usc.edu
> Subject: Re: Andrew McDonald response re: European iguanodonts
>
> Jaime Headden  wrote:
>
> >   If it weren't for various actions to stabilize the name *Iguanodon* (type 
> > species, type specimen) away from the teeth, we'd be dealing with another 
> > taxon nominative of a group from which is
> > couldn't be reasonably compared, a la *Titanosaurus* and *Troodon*.
>
>
> Agreed. _Troodon_ is a ticking time-bomb. The taxon _T. formosus_
> was established upon a tooth; but numerous other remains have been
> referred to this species, including a fragmentary skeleton named
> _Stenonychosaurus inequalis_ and a dentary named _Polyodontosaurus
> grandis_, from various horizons. It's not likely that all this
> material comes from a single species, which would mean that the _T.
> formosus_ tooth morphology is shared by more than one species. Under
> these circumstances, either _T. formosus_ is a nomen dubium, or a new
> holotype (neotype) would be designated in order to keep the genus
> _Troodon_ as a valid taxon (as was done with _Iguanodon_). If the
> former, we would go back to calling the family Saurornithoididae.
>
>
> A neotype (a partial skull) was also proposed for _Carcharodontosaurus
> saharicus_, a taxon also founded upon teeth (now lost) (Brusatte and
> Sereno, 2007). The risk here is that if _Carcharodontosaurus_ became
> a nomen dubium, the genus _Sigilmassasaurus_ would be available to
> receive the diagnostic material referred to _Carcharodontosaurus_ -
> assuming that the two are synonymous.
>
>
>
>
> Cheers
>
> Tim
>
>
>
>
> Cheers
>
> Tim