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Re: "Sleeping Dragon" (Psittacosaurus)

It seems to me that the phylogenetic signal from sleeping position may be weak, 
at best.  Because of the need to keep warm and the uniform physics of thermal 
conductance, this behavior seems to me a likely candidate for convergent (if 
not parallel) evolution.  Not that I'm saying birds didn't inherit the posture 
from their non-avian theropod ancestors; but by itself it wouldn't be terribly 
convincing evidence of direct ancestry.

Scott Hartman
Zoology & Physiology
University of Wyoming
Laramie, WY 82070

(307) 742-3799