[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

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

--- "Jaime A. Headden" <qilongia@yahoo.com> wrote:

> Tim Donovan (uwrk2@yahoo.com) wrote:

> I hardly doubt Mongolia was sans
> plants capable of producing pollen, so it MUST be
> there or had been there, even
> if subsequently removed or destroyed. 

 For the most part it just wasn't preserved in the LK
of Mongolia. Palynomorphs have been found in the Arts
Bogd area but not in the Nemegt AFAIK, although the
latter has yielded some plant fossils.

> <And Mesolanistes, conchostracans etc.>
>   See, selective taxonomic categorization and
> ignoring other dating methods
> (such as magnetostratigraphy and radiometrics of
> clastics!) doesn't help. 

 As I pointed out before, the Maastrichtian age of the
Nemegt is based on a variety of evidence, including
radiometric dating of underlying beds. See The Age of
Dinosaurs in Russia and Mongolia.

> <Again, Norman considered S. angustirostris and S.
> osborni to be virtually
> indistinguishable.>
>   Just
> because _A_ researcher considers them identical
> doesn't mean 1) they are or 2)
> that their ages were the same. As I explained
> before, named avian genera and
> even modern species can exists for 20+ million
> years, based on minimal
> morphological change.

 But this wasn't generally true of large LK dinosaurs.
Dodson noted that few genera spanned more than one
stage. Saurolophus is only known from early
Maastrichtian units 3 and 4 of the Horseshoe Canyon.

> Turnover among large dinosaurs
> was faster. Saurolophus is
> unknown from the Campanian or late Maastrichtian. 

>   As for *Saurolophus*, this still doesn't mean both
> species across the Pacific
> were the exact same age 

  Maybe not the EXACT same age but researchers have
considered a similar age parsimonious. See e.g. Lucas
Vertebrate Biochronology of the Mesozoic of China, and
Vertebrate Biostratigraphy and Biochronology of the
Cretaceous of China. I believe Osmolska and J. Wagner
have a similar view.

>since they are likely to
> have a common descent which
> is, logically, OLDER than either. So if we were to
> find this ur-*Saurolophus*,
> would we call it *Saurolophus* even? 

  Maybe Prosaurolophus. A species of Hypacrosaurus,
intermediate between Lambeosaurus and H. altispinus,
is known from the upper Two Medicine, but it is
clearly distinct from the Maastrichtian species. I
think the same would be true if the ancestor of S.
osborni turns up there.

> comes from this or that
> paper, a lot of them seemingly from Shukhov.

 SHUVALOV! Martinson and Sukhanov had the same view.

Yahoo! Mail - PC Magazine Editors' Choice 2005