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Re: Sinornithomimus sociality and the Polish theropod



Brad McFeeters wrote:

<Varricchio, D.J., P.C. Sereno, Zhao X., Tan L., J.A. Wilson & G.H. Lyon, 2008. 
Mud-trapped herd captures evidence of distinctive dinosaur sociality. _Acta 
Palaeontologica Polonica_ 53(4):567-578.  

Dzik, J., T. Sulej & G. Niedzwiedzki, 2008. A dicynodont-theropod association 
in the latest Triassic of Poland. _Acta Palaeontologica Polonica_ 
53(4):733-738.>

  The Dzik, Sulej and Niedzwiedzki paper at least gives us more information on 
the "rhino-sized" kannemeyeriid dicynodont (it really is huge), and the 
"theropod" whose identity was discussed. Possibly one of the more important 
elements of the latter is shown in some detail, the femur, but while the femora 
are often important for diagnosing dinosaur attributes, although the ilium and 
tibia can be just as if not more important, a curious extension and development 
of the olecranon of the ulna is rather distinct. This element enforces not only 
a quadrupedal posture, but argues for a design and stance that are unlike those 
found in basal dinosaur ancestry, much less theropod ancestry. The ulna, while 
relatively straight, lacks the significant reduction of a theropod, and that 
the arm was a body-weight supportive limb, which would mean any other 
development of the skeleton towards a theropod condition would have been likely 
only due to convergent cursoriality.

  On the other hand, Varricchio et al. describe the *Sinornithomimus* bonebed 
and include new prepared material which really sets up the distinct condition 
of this site, as several of these intact specimens were preserved with their 
legs and arms buried deep into the strata, crossing layer zones, and perturbing 
underlying layers of mud. Despite this, these fossils show the typical 
"dehydrated" posture of the dorsally curved spine and highly retracted (often 
into a complete circle) neck. Several of these animals are preserved in "life" 
poses, set up vertically, while others are ling on their side. Not a single one 
of them was adult, showing aggregation of a herd, perhaps, through catastrophic 
events.

  Cheers,

Jaime A. Headden

"Innocent, unbiased observation is a myth." --- P.B. Medawar (1969)