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Re: Everything you know about the Iren Dabasu age is (right)

 The Iren Dabasu therizinosaur fauna still appears to
have much more in common with that of the
Bayanshirenian of Outer Mongolia than it does with the
Nemegtian.  Iren Dabasu types appear very similar to
Bayanshiree forms; both were medium sized, common and
diverse, whereas Therizinosaurus was big and rare.

How many known segnosaur specimens are there from all three formations together? 5? Certainly less than 10, no? How do you intend to make statistically meaningful statements based on that kind of sample size...?

In addition, you're trying to do biostratigraphy with _the evolutionary "level" of_ big, rare terrestrial vertebrates. This is highly prone to fallacies.

 Not necessarily. Recall J. Wagner's remark that
palynomorphs have a nasty habit of showing up at
different times in different places. I suspect that is
true with regard to the Tsagayan and Hell Creek, and
the apparent synchrony is illusory.

Palynomorphs still have big advantages: they occur in exorbitant numbers, making statistics applicable; and they are spread by wind, which means they have the potential to correlate terrestrial and marine sediments (which is usually almost as good as getting an absolute age for the terrestrial ones).

I note btw that
Mesolanistes, indicative of a Maastrichtian age, is
not AFAIK, known from the Tsagayan.

It's indicative of a Maastrichtian age _and a certain environment_. Look at the snail species around you. Is there any that occurs in rainy forests and in semideserts alike?