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



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).