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

--- Michael Mortimer <mickey_mortimer111@msn.com>

> There has been no published evidence for any
> Erlikosaurus or Segnosaurus 
> remains outside of their holotypes and (in
> Segnosaurus) paratypes.  Sure 
> Currie and Eberth reported elements which were
> 'identical' in 1993, but then 
> in 2001 and 2002 we get two new Iren Debasu
> therizinosauroids.  Until the 
> old remains are compared with these new taxa, the
> referral is very weak.

  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.

> Remember, Mononykus, Avimimus, Saurornithoides and
> Velociraptor have all 
> been reported from Iren debasu as well, and are all
> Djadockhta/Nemegt age.  
> But Currie and Dong (2001) later modified Currie and
> Eberth's referral from 
> Saurornithoides to Troodontidae indet..  I've seen
> figures of the Iren 
> Debasu Avimimus remains, and how are we to tell if
> they're Avimimus 
> portentosus, A. sp. nov., or another genus of
> avimimid?  They differ a bit 
> from the A. portentosus specimens, but determining
> what it means is pretty 
> subjective.

 Turnover among small theropods was apparently not as
fast as turnover among larger dinosaurs. Ornithomimus
is known from the Campanian to the end of the
Maastrichtian. It wouldn't be surprising if some Iren
Dabasu theropods were very closely related to Nemegt
counterparts, even if the temporal difference were

> Basically, the take-home message is that dinosaur
> biostratigraphy sucks and 
> should not be used except very generally. 
> Invertebrates, pollen, 
> charophytes - those are useful.

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

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