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



I couldn't agree more... give me ammonites and pollen
over dinosaurs any day (strictly for biostratigraphic
purposes, of course)... :-)  

Magnetostratigraphy and radiometric dates are even
better, since one does not have to worry about time
transgressive first/last appearances producing errors
in age estimations.

Guy Leahy



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

> Tim Donovan wrote-
> 
> >   Iren Dabasu has other taxa in common with the
> >Bayanshirenian beds of Outer Mongolia. Erlikosaurus
> >and Segnosaurus are known from Baishin Tsav as well
> as
> >Iren Dabasu. Segnosaurus is also known from Khar
> >Hotol, where the boundary between the Bayanshiree
> and
> >Djadokhta formations occurs.
> 
> 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.
> 
> 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.
> 
> Basically, the take-home message is that dinosaur
> biostratigraphy sucks and 
> should not be used except very generally. 
> Invertebrates, pollen, 
> charophytes - those are useful.
> 
> Mickey Mortimer
> 
> 
>