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RE: Juramaia, Jurassic eutherian from China



http://www.nature.com/nature/journal/v476/n7361/extref/nature10291-s1.pdf

Excerpt from supplementary:

Part C. Geological Age of Juramaia and Tiaojishan Formation

The holotype specimen (BMNH1343) from Tiaojishan Formation is estimated to
be 160
million years old. This estimate is based on the following geochronological
studies.
The Tiaojishan Formation was dated to be 165-164 Ma by SHRIMP U-Pb method on
zircons in the Qiaomailiang Locality in the neighboring Ningcheng area of
the Inner
Mongolia Region (fig. 2 in Liu et al. 2006; also 61-Liu and Liu 2005). The
Lanqi
Formation in the adjacent Beipiao area of Liaoning is generally considered
to be a
stratigraphic equivalent of the Tiaojishan Fm. The lower part of Lanqi
Formation in the
Beipiao area near Jianchang County is recently dated to range to 160.7±0.4ma
to 158.7±0.6ma by high-precision 40Ar/39Ar geochronological method on
sanidines and
plagioclases.

An earlier estimate postulated the geological age of the Tiaojishan
Formation to be from
161ma to 151ma (62-Xu et al. 2003, cited by 63-Hu et al. 2009). Another
geological study
estimated that the top part of Tiaojishan be range from 162ma to 154ma
(64-Zhang et al.
2008). A recent study on a feathered troodontid dinosaur from the Tiaojishan
Fm. (Hu et al.
2009) adopted the estimate from K. Xu et al. (2003) (62) for the Tiaojishan
Formation.
The Hu et al. (2009) (63) tudy assigned the troodontid dinosaur from
Tiaojishan in Daxigou
site to be ~155 ma (about the median age from the range of 161 ma to 151ma,
according to
Xu et al. 2003[62]).

On the basis more recent work, especially the direct dating on the
Tiaojishan Fm (15-Liu et
al. 2006) and by the more precise geochronological method to date the Lanqi
Formation
(Tiaojishan-equivalent) in adjacent regions (16-Chang et al. 2009), we
believe that 160 ma
for the fossiliferous horizon of Daxigou site is a better estimate. By a
common used
geological timescale by Gradstein et al. (2004) (65), this fossil locality
should be placed in
the lowest part of the Late Jurassic.

For faunal correlation, the Tiaojishan Formation of the Jianchang County
also yielded the
pterosaur Darwinopterus modularis (66-Lü et al. 2009) and the troodontid
dinosaur
Anchiornis huxleyi. Hu et al. (2009) (63) pointed out that the invertebrate
and plant fossils
from the Tiaojishan Formation differ from, and are generally more
plesiomorphous than
those of the Early Cretaceous Yixian Formation. We concur with this
assessment, and
suggest that the Tiaojishan fossil biota is distinctively older than the
Jehol biota of the
Yixian Formation. Ultimately, the series of fossiliferous sites in the
Tiaojishan Formation
in the Jianchang County should be directly dated, by more thorough field
sampling of
igneous and volcanic materials collected on the sites.


--Mikko H.


*******************************************************************
Mikko K. Haaramo
Vertebrate paleontologist
Departement of Geosciences & Geography
Subdepartment of Geology
PL 64 (Gustaf Hällströmin katu 2a)
FIN-00014  University of Helsinki

tel: +358-9-191 50821
email: mikko.haaramo(at)helsinki.fi
*******************************************************************





-----Original Message-----
From: owner-DINOSAUR@usc.edu [mailto:owner-DINOSAUR@usc.edu] On Behalf Of
David Marjanovic
Sent: 25. elokuuta 2011 0:00
To: DML
Subject: Re: Juramaia, Jurassic eutherian from China

>  And now I have to update the webnotes for class... :-)
>
>  Thomas R. Holtz, Jr.

And now I'm getting deeply interested in the stratigraphy. Is it from 
the Daohugou Beds? If so, is it _really_ from the Daohugou beds? And how 
old are _they_ really? Really really?

Lithostratigraphic correlation in northeastern China is clearly very 
difficult. There are hairpin-shaped layers, and much of the area 
consists of 1000 m high rolling hills, one after the other for hundreds 
of km in every direction.