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