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Re: An Odd Question on Tyrannosaurs.....



On Sunday, July 7, 2002, at 01:05 AM, Mickey Mortimer wrote:

MariusRomanus@aol.com wrote-
 
> Are there any indications at all..... and I mean even in the slightest bit...... that tyrannosaurs had
> unicates that were not ossified?.....
 
Yes, there are many indications they had unossified uncinate processes, in the form of several complete articulated specimens without them.  I'm sure tyrannosaur expert Tom Holtz could verify he's never seen one.
 
> Obviously the monsters had a cartilaginous sternum to start with.
 
But they didn't.  At least some (eg. Gorgosaurus, Tyrannosaurus bataar) had ossified sterna.

Brochu showed at the mexico SVP meeting that Lambe's Gorgosaurus "sternum" is actually two fused pairs of gastralia, offhand I don't know of any tyrannosaurid that preserves an ossified sternum. I don't know of any theropods outside of Tyrannosauridae that have this gastralia structure either (its present in both T. rex and Gorgosaurus libratus) so it may be a synapomorphy of the group.
Unossified uncinate processes may have been present, for example cartilages are present on the posterior of the ribs of "Willo". I think they are actually pretty widely distributed which would explain how they pop up again (ossified) in tuataras. Probably the sternum was present, ossified or otherwise, in all dinosaurs.