A non-Jurassic non-beaver

[David Marjanovic <david.marjanovic@gmx.at>]

----- 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.