Re: Age of the Barun Goyot, Djadoktha and Nemegt Formations

[Tim Williams <twilliams_alpha@hotmail.com>]

Jaime Headden wrote:

>   But maybe I can counter Donovan's statement above by saying that someone 
> else
> thinks that the two *Saurolophus* species are different genera? Researcher 
> vs.
> researcher, who will win!? (While I'd bank on Norman for his credentials, I 
> and
> others will note he tends to be a lumper and has dismissed variation in
> geographic areas due to individual variation,

Several ornithopod species that have been "lumped" in the same genus are 
currently in the process of being de-lumped (or should that be un-lumped?).  
(For example, one famous ornithopod genus is about to be pared down in 
dramatic fashion.)  However, although Norman apparently has a reputation as 
a "lumper" (see above), he did recognize that _"Probactrosaurus" 
mazongshanensis_ does not belong in the genus _Probactrosaurus_ (among other 
features, the dentary tooth crowns of _mazonhshanensis_ more closely 
resemble those of _Altirhinus_ than _P. gobiensis_).

Norman D.B. (2002). On Asian ornithopods (Dinosauria: Ornithischia). 4. 
_Probactrosaurus_ Rozhdestvensky, 1966. Zoological Journal of the Linnean 
Society 136: 113-144.

And while certain parts of the euornithopod tree may be "lumpy", other parts 
may be oversplit when it comes to the number of genera.  Just look at 
_Hypacrosaurus_, _Corythosaurus_ and _Lambeosaurus_, or _Edmontosaurus_ and 
_Anatotitan_.  The same is pretty much true for advanced ceratopsids.  The 
validity of genera often lies in the eye of the beholder, and so makes for a 
poor yardstick in biostratigraphy.

Cheers

Tim (not Donovan).