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YIXIAN = J OR K?
Jim Kirkland wrote...
> I have heard that the Chinese are getting ready to publish a paper
> in Science or Nature giving new radiometric Ar/Ar dates from ashes
> within the Yixian Formation lucustrine beds giving dates of around
> 142-140 mya (pretty basal Cretaceous). Certainly as the
> Psittacosaurs have pemaxillary teeth they are more primitive than
> any so far described. I think we had all better wait and see.
Paul Davis has been covering the respective ages of the Yixian and
Jiufuotang Fms in his recent talks on early bird evolution, and in
the abstract to his talk given at the Cretaceous Biodiversity
Conference (Portsmouth '98) he writes..
'The ages of these formations is surrounded in controversy at the
moment, basically due to differing dates obtained from different tuff
horizons. However all researchers agree that the formations range
from Upper Jurassic to the Lower Cretaceous with the Yixian Formation
underlying the Jiufuotang Formation.
'The older Yixian Formation has yielded a monospecific avian
assemblage (_Confuciusornis sanctus_) and is dated as 141+/- 6 Ma
(combined K-Ar, Rb-Sr data). This makes _Confuciusornis_ comparable
in age to _Archaeopteryx_.....'
Ah, but does it? Isn't there is also some controversy over the exact
date of Solenhofen: Kimmeridgian or Tithonian? I am aware of some
published work that attempts to resolve this issue, but do not have
it to hand. It has been discussed on the list before.
Paul's abstract has just been published in _Europal_ 13 (Sept 1998),
as are all the other abstracts from the Cretaceous Biodiversity
Conference. Other tetrapod ones are Benton on European and African
Cretaceous dinosaurs, Evans on Cretaceous diversity of lepidosaurs
and lissamphibians, Martill on Crato Fm aerial organisms, Naish on
Wealden Group theropods and Unwin on pterosaur evolution. From a
personal perspective this conference was especially interesting as I
tried to give my presentation after spending all of lunchtime in the
pub... this was not wise.
"People see woodlice and report armadillos"