Re: Yixian Dating Again

["Jaime A. Headden" <qilongia@yahoo.com>]

  Accidentally sent this to David alone...

> David Marjanovic (david.marjanovic@gmx.at) wrote:
> 
> <Meanwhile revised AFAIK. Weren't they whole-rock ages while the K dates
> are based on individual crystals, or am I mixing this up with something?
> There are other radiometric dates (also Ar/Ar IIRC) that suggest
> Barremian
> for Sihetun.>
> 
>   Yes. I beleive Lo et al., used a whole congolomerate, whereas other
> studies used single-grain sampling. However, U/Pb sampling and Ar/Ar
> sampling also provide similar _and_ dissimilar results.
> 
> <*Hadrocodium* is from Yúnnán, more than 3,000 km to the southwest, and
> from the Early Jurassic.>
> 
>   You know, it used to be Yünnan, then you transcribe Yúnnán, I wonder
> why
> not just use simplified syllabaric approximations? Chinese lacks
> diacritics.
> 
> <Would say nothing either way, if *Aristosuchus* and/or that pelvis from
> Santana is compsognathid, too.>
> 
>   Both appear to correlate very well to *Compsognathus*. *Scipionyx*
> seems
> similar and/or transitional between *Compsognathus* and *Ornitholestes*
> in
> quality, and *Sinosauropteryx*, despite the third specimen, looks like
> it
> si compsognathid in the broadest sense. It is notable that a
> plesiomorphy
> does not always mean it is more basal than the Comp + birds node, but
> that
> it is just more primitive; it may _be_ more basal, but not neccessarily
> --
> a cladistic analysis often has difficulty telling the difference.
> *Sinosauropteryx* may be a primitive compsognathid, and the trees still
> support a close phyletic space between the two.
> 
> <Well, the tail is from a *Microraptor*, isn't it? There's a second
> anurognathid from the Yixian Fm, *Jeholopterus* from Inner Mongolia. The
> authors 
> 
> Wang Xiaolin, Zhou Zhonghe, Zhang Fucheng & Xu Xing: A nearly completely
> articulated rhamphorhynchoid pterosaur with exceptionally well-preserved
> wing membranes and "hairs" from Inner Mongolia, northeast China, Chinese
> Science Bulletin 47(3), 226 -- 232 (February 2002)>
> 
>   I have this ... it's not an anurognathid. Not close.
> 
> <Yes. I just mean it's suggestive, and it neither contradicts an EK age
> nor suggests a LJ one. -- AFAIK no J angiosperm pollen are known,
> right?>
> 
>   There is plenty of pollen from the Jurassic and Cretaceous that were
> offered as earliest angiosperms, but most have beein either disproven,
> or
> the rest subsumed to ambiguity or bad preservation. This is true of all
> the Jurassic palynomoprh studies.
> 
> <Would you say the teeth from Guimarota, not to mention the MJ ones from
> England, look like known troodontids? (I can't tell.)>
> 
>   I have not seen these teeth, and have been very interested in them for
> a
> while... just no opportunity to get the book, or find the papers on many
> isolated teeth in discussion. I tend to look at morphotypes more than
> anything that might be taxonomically important. But I am interested in
> these Guimarota teeth in specific. All of them ... lol.
> 
>   Cheers,
> 
> =====
> Jaime A. Headden
> 
>   Little steps are often the hardest to take.  We are too used to making
> leaps in the face of adversity, that a simple skip is so hard to do.  We
> should all learn to walk soft, walk small, see the world around us
> rather than zoom by it.
> 
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