Re: More on Moser and prosauropod sacrals

["Jaime Headden" <ja_headden@qilong.8m.com>]

Dear Dr. Moser and the list,

  My only comment on this issue will be observation on one specimen of 
*Silesaurus,* ZPAL Ab III/404, in which the sacrum is a
unified object of four vertebrae, comprising dorsosacrals 1 and 2, plus the two 
primordial archosaurian sacrals, and no caudosacral,
based on the large size and contact of sacral ribs and ilia in the last two 
elements. Despite this, the dirst dorsosacral is fused
to the second, but is almost complete anterior to the anterior extent of the 
ilium, and does not contact it. It is, essentially, a
fused "lumbar," being a dorsal without facets for the ribs, and thus 
*Silesaurus* may be described as having a synsacrum. The reason
I mention this is the exclusionary data for defining possible dorsosacrals (or 
caudosacrals) based on how many vertebrae are defined
by extent of the preacetabular alae or contact with the ilium. As this is a 
primitive near-dinosaur (or possible dinosaur), it seems
particularly relevant in considerations of possible sacral compositions in 
experimentations in other basal dinosaurs, including
"prosauropods" as to sacral recruitment.

  Cheers,

  Jaime A. Headden

  Little steps are often the hardest to take. We are too used to making leaps 
in the face of adversity, that a simple skip is so
hard to do.  We should all learn to walk soft, walk small, see the world around 
us rather than zoom by it.

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