Re: Sinosauropteryx at Dinofest

[smithjb@sas.upenn.edu (Joshua Smith)]

Allan Edels wrote:
> 
> Mike:
> 
>     You could be right - of course, it might be younger - Aptian, maybe.
> (Josh - Are you lurking somewhere? - Can you correct me here?).
> 
        OK. Here is what I know about the age of Sihetun.  We have a good 
Ar-Ar date on the most basal basalt/andesite of the Yixian Formation, from 
close to the Sihetun Quarries.  This date is 121.9 Ma (+/- a couple, as 
always), which puts Sihetun in the Barremian.  It is a good date, not 
great, as the laser technique still has some problems with it (however, 
as I am a paleoecologist, I am not really familiar with all of the 
details of those problems).  We are looking to get zircon dates from 
tuffaceous sediments in the area.  This would bring our confidence level 
on the dates up to around 95% where we want it.
        We also have basalt samples from the overlying flow unit (the 
Sihetun Member 3 for those of you who were in Philly), and are in the 
process of getting numbers off of them.  This will allow us to further 
contrain the age of the most basal sedimentary intercalation (the one 
with all of the goodies in it).  I am pretty sure that Sihetun is 
Barremian, but as I said in the talk, we don't have any idea of how long 
it took to emplace the lacustrine sediments at the site.  There are no 
data on sedimentation rates (and sedimentation rate data are almost 
always junk anyway) nor is there good control on whether or not we have 
temperal hiatuses within those sediments (they don't always show up at 
outcrop scale).   So yes, the Sihetun intercalation could even be younger 
than Barremian, especially the upper beds, but we don't have any data on 
that yet.  Give me a month or so and I should be able to let you know.  
Whichever, they are going to have to go a long way to convince me that 
those beds Jurassic-anything.

        Ok.  Since I know someone will ask, let's talk about the 
provenance of _Sinosauropteryx_.  I went into that talk assuming that 
Phil and I were on the same sheet of music as he didn't mention anything 
about his view BEFORE I went in there.  AFTER his talk, I yacked with him 
about it and said that he had talked to the people who had pulled the 
specimens out of Sihetun and they pointed him at the specific hole where 
_Sinosauropteryx_ is supposed to have come from.  These same people 
pointed me to a totally different area of the quarry, and had shown Dong 
a different area of it still.  Some of the other people we talked to were 
rather emphatic about the idea that no one really knew where the little 
buggers actually came from.  So, I guess I am still unconvinced and Phil 
and I are sitting on different sides of the fence on this issue. 
Whatever.  As long as people understand that there is a strong element of 
uncertainty concerning the specific relationships among the Liaoning 
fossils at this time.   This is really not that important of an issue until 
people start arguing things like the stratigraphic seperation between
_Protarchaeopteryx_ and _Confuciusornis_ and postulating a significant 
evolutionary span between them on the basis of that seperation.  I suspect I 
don't need to elaborate on what I think of that idea...

-Josh

-- 
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Josh Smith
Department of Geology
University of Pennsylvania
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