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Re: Mongolian Strata



>    Hi all,
>    
>        Sorry to bug everyone with this but I need answers. I'm 
>looking to find out what age range(s) the Gobi/Mongolia/China area 
>covers. From the fauna uncovered from there, I'm figuring it's at 
>least Upper Jurassic and (the lower side of)Upper Cretaceous, but I 
>would like to know for sure.

China, especially, has many diverse faunas from throughout the age of
Dinosaurs.  Chinese dinosaurs include some rare Late Triassic forms,
abundant Early Jurassic forms (the so-called _Lufengosaurus_ fauna), the
best Middle Jurassic fauna known (containing _Huayangosaurus_, _Gasosaurus_,
_Shunosaurus_, and _Omeisaurus_, to name a few) and excellent Late Jurassic
assemblages (containing _Sinraptor_, _Mamenchisaurus_, other sinraptorids
and euhelopodids, and a buttload of stegosaurians).

With regards to the Cretaceous, there are late Early Cretaceous units (the
_Psittacosaurus_ fauna, probably Aptian-Albian stages), and various Senonian
age (Coniancian, Santonian, Campanian, and Maastrichtian) units, although
the ages of each particular unit is not yet well constrained.  The Nanxing
basin contains latest Maastricthian-early Paleocene deposits, making it one
of the few regions in which the K-T boundary is preseved on land.

Mongolian dinosaurs, at least those I'm aware of, are all Cretaceous.  (By
"Mongolian", I refer to the old Mongolian People's Republic, and not Inner
Mongolia, which is an autonomous region in the People's Repbulic of China) .

The _Psittacosaurus_ fauna is well known from Mongolia.  According to Dave
Norman, the type specimen of _Iguanodon orientalis_ (which is NOT the
big-nosed Mongolian iguanodontian often illustrated) cannot be distinguished
from _I. bernissartensis_.  IF _I. orientalis_ belongs to the European
species, and IF _I. bernessiartensis_ had a typically short species duration
(two big "IF"s), then there are older Barremian deposits somewhere in
Mongolia.

The Bayn Shire fauna, once considered to be early Late Cretaceous, may in
fact be early Campanian (i.e., tens of millions of years younger than
previously supposed).  All the Late Cretaceous faunas of Mongolia may be
Campano-Maastrichtian (~86-65 million years ago), but the exact date is far
from certain.  Although the Djadochta-Barun Goyot-Nemegt series of faunas
has been interpreted as a temporal sequence (incidentally, indicating
increasing humidity in Mongolia at the end of the Cretaceous), these units
might only be generally contemporaneous, but from different environments.
In fact, part of the AMNH work in Mongolia is to sort out this problem.

Hope that answered your question.  To add a final note, the old southern
Asian Soviet Republics (Tajikistan, Kazakhstan, etc.) contain dinosaurs
which have been interpreted as Turonian age: that is, occuring between the
_Psittacosaurus_ fauna and the Bayn Shire. 

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661