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

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