[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: The timing of stegosaur extinction



Tim Donovan wrote-

> >  Gurvan Eran, Tevsh, Undurukhin and Tsagantsab
> >formations of Mongolia. I don't know in which of
> those
> >units or what other fossils show equivalence,
> though
> >Tugulu turtles "seem little changed from the late
> >Jurassic."
>
> The only dsungaripterid Unwin and Bakhurina (2000)
> report from anywhere in
> Mongolia is "Phobetor" parvus, which was previously
> named Dsungaripterus
> parvus.  This does not mean it can be used to
> correlate stratigraphy with
> Dsungaripterus weii though.
> Your turtle statement is too vague to be useful.

 AFAIK there are no stegosaurs in the c Barremian age
Mazongshan beds, nor in Mongolian or Chinese beds of
late early Cretaceous age, such as those which yielded
Chilantaisaurus. Is there any evidence that the
Lianmuqin is younger than Valanginian?

With all of ten or so stegosaur individuals known from anywhere in Cretaceous Asia, I don't think their absence in particular formations means much.
Have the beds Chilantaisaurus was found in yielded any dinosaurs except Chilantaisaurus itself, and a few indeterminate theropod elements?
My Lianmugin references are on campus, but Psittacosaurus xinjiangensis is known from there, right? In Liaoning, Psittacosaurus is restricted to Barremian-Albian, with Hongshanosaurus being present in the Late Valanginian-Hauterivian beds, and Chaoyangsaurus in the early Valanginian.


> Ah, but his table 14.2 includes absolute dates which
> are as recent as Aptian
> (e.g. upper part of Tsagantsav Svita 120 +/- 5 Ma).
> The Aptian started 125
> Ma (Gradstein and Ogg, 2004).


That doesn't make much sense, since the youngest putative Tsagantsabian dates overlap with those given for the younger Huhteeg Gorizont. Shuvalov was aware of those younger dates but evidently didn't take them seriously. IGEM dates have big margins of error and some are probably inaccurate. I note Lucas just used 130 Ma, apparently based on an average value.

They overlap in possible dates, but not definite ones. The youngest Tsagantsav date is 120 +/- 5 Ma, compared to the Huhteeg value of 116 +/- 8 Ma. So the Huhteeg could be 108 Ma, and that part of the Tsagantsav 125 Ma, for instance. The IGEM margins of error are comparable to the ARGI ones, the latter of which include a date that's latest Hauterivian at earliest (and mid Aptian at latest).


> I await this forwarded post.

 Actually it wasn't put onlist but you should have it
by now.

Nope.

Mickey Mortimer