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Re: The timing of stegosaur extinction



Tim Donovan wrote-

> > Early Cretaceous, Sand Wells Formation (USA),
> > ?Stegosauridae indet..
>
>    What is the age of that unit? Not long ago, there
> was a report of Stegosaurus in Siberia, indicating a
> connection with NA. In light of that, and the close
> affinitiy of Stegosaurus and Wuerhosaurus, I think the
> latter may have been present in NA early in the K. But
> recently the Yellow Cat-lacking stegosaurs- has been
> redated to c Aptian, indicating a very long gap
> between the Morrison record and the first good early
> Cretaceous record in NA. The Asian and NA records
> suggest stegosaur extinction occurred before the
> Aptian.

Don't know a more precise age.  These ages were all from The Dinosauria 2nd
Ed..
A close affinity of Stegosaurus and Wuerhosaurus has not been shown to
exist.  In Galton and Upchurch's (2004) analysis, Wuerhosaurus is variously
placed as sister to Stegosaurus, or to (Stego(Lexovi,Hespero)).
The Yellow Cat Member is supposed to be Barremian, where's this Aptian
redating from?

> > Barremian, La Amarga Formation (Argentina),
> > Stegosauria indet..
>
>   Barremian? I thought it was Hauterivian.

According to Leanza et al. (2004), the Puesto Antigual Member of the La
Amarga Formation is Early Barremian.

>   Didn't Russell mention possible stegosaur remains
> from the late early Cretaceus of Morocco?

Apparently it's a stegosaur-like femur based only on a photograph (Russell,
1986).

> > Early Cretaceous, Potton Sands (England),
> > Craterosaurus pottonensis.
>
>   Wasn't that material reworked?

Yes, but presumably from Early Cretaceous age, since Iguanodon cf.
bernissartensis is preserved there.

> > Valanginian-Albian, Tugulu Group (China),
> > Wuerhosaurus homheni.
> > Valanginian-Albian, Qaganur Formation (China),
> > Stegosauria indet..
> > Early Cretaceous, Ejinhoro Formation (China),
> > Wuerhosaurus ordosensis.
>
>   I think Wuerhosaurus was no younger than about
> Valanginian. An Aptian-Albian age seems outdated and
> dubious. Wuerhosaurus homheni was of Tsagantsabian
> age, and Shuvalov wrote that Tsagantsabian sediments
> had already begun to accumulate by the end of the
> Jurassic. According to Lucas, W. ordosensis also
> appears to be of Tsagantsabian age.

Early Cretaceous Asian formations seem inadequately dated for the most part.
Lucas and Estep (1998) say "key taxa of biochronological value" for
Tsagantsabian age are Prodeinodon, Asiatosaurus, Psittacosaurus and
Dsungaripterus.  But both Prodeinodon and Asiatosaurus are currently
indeterminate, so no remains besides the Huhteeg Svita holotypes can be
referred to them.  Psittacosaurus is said to also be in the younger
Khukhtekian sediments, and indeed is known from Late Barremian-Early Albian
times in Liaoning.  Has Dsungaripterus been found outside its type locality?

> > Maastrichtian, Kallenkurichi Formation,
> > Stegosauridae indet..
>
>   Didn't Galton and Upchurch recently resurrect
> Dravidosaurus, considered by Chatterjee to be a
> plesiosaur?

Yes, but without reason or discussion.

Mickey Mortimer
Undergraduate, Earth and Space Sciences
University of Washington
The Theropod Database - http://students.washington.edu/eoraptor/Home.html