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A non-Jurassic non-beaver



----- Original Message -----
From: "K and T Dykes" <ktdykes@arcor.de>
Sent: Friday, February 24, 2006 1:31 PM
Subject: Re: A Jurassic 'beaver'

Thanks to a kindly List Member, I've got the description of /Castorocauda/,
the Supplementary Online Material, the commentry from Thomas Martin and a
Science Press Release. The Supplementary Material has further information
on the basis of the age assessment. There are two radiometric datings of
relevance and the following is from page 3.


"Geological Age and Stratigraphical Horizon:

The holotype specimen of JZMP04117 was discovered at the Daohugou Locality
(N41°18.979', E119°14.318') of Ningcheng County of Inner Mongolia
Autonomous Region. The fossil is from Bed 3 of the Jiulongshan Formation
(sensu Ren et al. 2002). The fossiliferous bed yielding JZMP04117 and other
fossil vertebrates are 20 meters below the volcanic ash beds dated at
164.2±2.5Ma from feldspar by 40Ar/39Ar dating, and at 164.6±2.4Ma from
zircon by SHRIMP 206Pb/238U dating (Chen et al. 2004; Ji et al. 2004).
Therefore the fossil beds of JZMP04117
are approximately 164 ma and their age should be the Middle Jurassic."

The paper I reported here http://dml.cmnh.org/2005Sep/msg00329.html disagrees in no uncertain terms with the idea that the Daohugou Bed belongs to the Jiulongshan Fm. Importantly, the Daohugou Bed is above, not below, the Bathonian-to-Oxfordian ash layer (...which could even be Kimmeridgian, actually... http://www.stratigraphy.org/gssp.htm gives huge uncertainties for all age boundaries around these dates). All in all the data presented in that paper point to a Valanginian to Barremian age -- anywhere between the underlying (!!!) Tuchengzi Fm (whose "upper part" is about as old as the Berriasian-Valanginian boundary) and the probably overlying Yixian Fm.


It should be interesting to find out where the presumably (!) Hauterivian Dabeigou Fm (home of *Protopteryx*) fits into this.

The paper on *Jeholotriton* in the September JVP even equates the Daohugou Bed with the Yixian Fm (Barremian-Aptian boundary), though this may be too much.

Thanks for reminding me of *Sibirotherium*! I did deliberately ignore *Reigitherium*. I didn't know the unnamed material.