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

--- tholtz@geol.umd.edu wrote:

> Except, of course, that the Bayn Shire small
> tyrannosaur material hasn't
> been demonstrated to actually come from
> Alectrosaurus olseni, which is at
> present a poorly diagnosed taxon.

  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. So it certainly appears
that Iren Dabasu correlates with the Bayanshirenian
strata which underlie the Djadokhta. But Baishin Tsav
and Khar Hotol are said to represent the upper part of
the Bayanshiree Svita, probably around the end of the
Santonian. Therefore it is likely that ostracods and
other microfossils from apparently equivalent beds of
Iren Dabasu did not long predate the
"Campanian-Maastrichtian" age they are considered
representative of. Such microfossils must have been
present earlier and persisted into later periods,
whereas most Bayanshirenian dinos did not.

> Actually, given that the Iren Dabasu has had far
> from a great number of
> field seasons, I would be cautious about saying
> what's really there.

  A great deal was found there by P. Currie years ago
and reported in Geotimes. AFAIK there were no
Nemegtian dinosaurs. A turtle, Khunnuchelys, is known
from Iren Dabasu, and differs from Nemegtian and
Maastrichtian turtles.

> Much like I would be cautious about dismissing the
> stratigraphic
> conclusions of a paper prior to reading it. (Yes, I
> admit: I'm pretty
> skeptical. 

  With very good reason.

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