Re: Ornithodesmus (Was Re: CRETACEOUS STEGOSAURS)

["Jaime A. Headden" <qilongia@yahoo.com>]

Simon Clabby (dinowight@yahoo.co.uk) wrote:

<Well, apart from the lack of dorsoventrally flattened transverse
processes, I'm not sure about dromaeosaurs, but the factors that attribute
it to the Coelophysoids and the abelisauroids are (and I quote from
Martill and Naish's excellent 'Dinosaurs of the Isle of Wight')
"...ankylosis of at least four sacrals, a sacrum with six sacrals, and a
neural spine laminae...", and it's fenestral sacral plate is reminiscent
of coelophysoids.>

  I'd hate to say this, though aside from the zygapophyseal laminae, the
sacrum is similar to ornithomimosauria, oviraptorid, caenagnathid,
troodontid, as well as dromaeosaurid sacra by the same features that would
suggest it was abelisaurian or coelophysoid. That it bears a pleurocoel on
only the first  two sacrals is a primitive feature. The zygapophyses do
form a continuous lamina (Howse and Milner's "neural platform"), and
dromaeosaurids do not neccessarily need to bear dorsoventrally flattened
sacral ribs. Affinities to more advanced theropods than non-tetanurans
like abelisaurids or coelophysids can be found in the wider central than
tall, the shallower last sacral caudal face to width, than to the first
sacral cranial face, showing the caudal vertebrae began much smaller and
broader in their centra than the dorsal vertebrae; the sacral ribs also
progress ventrally onto the centra, and advanced feature found in
near-birds. The strong arching of the sacrum is unique, apparently. This
form is not likely to be anything but a maniraptoran.

  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)

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