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darren.naish@port.ac.uk wrote:

> Thanks to Josh for his thoughts on the age of the Liaoning beds. One
> quick comment. Josh wrote...
> > To use _Sinosauropteryx_, for example, to
> > support a Tithonian age for the basins that contain it because it
> > looks like a Tithonian form, is fraught with problems when the sample
> > size is in the single digits and all of the specimens come from within
> > the rocks in question themselves.
> Furthermore, there are other very _Compsognathus_-like forms from
> indisputable Cretaceous rocks (Owen 1876, Naish 1999, Martill et al.
> 2000). And incidentally, as Nick Longrich has discussed here before,
> the type specimen of _Sinosauropteryx prima_ is pretty clearly not that
> similar to _Compsognathus_. HOWEVER, GMV 2124 (the second
> specimen - one with mammal jaws in its gut) is similar to
> _Compsognathus_ (and thus probably a compsognathid).
> Hopefully the thing with _Sinosauropteryx_ will eventually get
> published.

I sincerely appreciate Darren's thanks.  The only comment that I would make
here, and this was the point that I was going for, is that we need to
remember that unless we have many (a few hundred) specimens of these
_Compsognathus_-like forms, they themselves don't tell us much at all about
the age of the rocks.  The evidence for the sediments being "indisputable
Cretaceous rocks" needs to come from data other than the tetrapod fossils
contained in them unless these compsognathids are very abundant,
geographically very widespread, and known from a very short time span.  I
especially agree with Darren in the hopes that more detailed descriptions
are forthcoming.


Josh Smith
Department of Earth and Environmental Science
University of Pennsylvania
471 Hayden Hall
240 South 33rd Street
Philadelphia, PA  19104-6316
(215) 898-5630 (Office)
(215) 898-0964 (FAX)