Yixan Age

[Josh Smith <smithjb@sas.upenn.edu>]

> From: Mickey Mortimer 
> Some specific critiques-
> Hou continues to state the Lower Yixian Formation is Late
> Jurassic, when it is Middle Barremian.  Thus, though he says
> Confuciusornis, Liaoningornis, Eoenantiornis and Liaoxiornis
> were the earliest pygostylians, there are taxa from Spain,
> England, Mongolia and North Korea which predate or coexisted
> with them (http://www.cmnh.org/dinoarch/2002Jan/msg00544.html). 
> Thus, his conclusion that enantiornithines evolved in East Asia
> is unfounded.

Well, while I certainly am of the opinion that the available data point 
toward a Middle Barremian age as more viable than a Tithonian one, 
saying that the Yixian IS Middle Barremian is wrong for the same 
reasons that the supporters stating emphatically that these rocks ARE 
Tithonian.  To quote Kevin Padian a few years ago on whether birds 
evolved from dinosaurs or not "guys, were aren't ever going to know."  
The most reliable data, interpreted as reliable according to current 
interpretations of the mechanics of science, are more indicative of a 
Barremian age than they are of a Tithonian age.  Indeed strongly so.  
However, this is the best that we are going to get.  
While one would think that given the Swisher et al. and Smith et al. 
2001 papers would have pretty resolved this "contentious" issue, but 
the newest _Archaefructus_ paper would suggest otherwise.  But that is 
ok.  We are on it...

-J

----
Josh Smith
Department of Anthropology
Harvard University
18 Traymore Street
Cambridge, MA 02140
Office: 617.495.1966
Director, Bahariya Dinosaur Project http://egyptdinos.org

After 1 August:
Josh Smith
Assistant Professor of Geology
Department of Earth & Planetary Sciences
Washington University
Campus Box 1169
1 Brookings Drive
108 Wilson Hall
St. Louis, MO 63130-4899
Office: 321 McDonnell Hall
Phone: 314-935-4258  FAX: 314-935-7361
smithjb@levee.wustl.edu
http://epsc.wustl.edu