STEGOSAUR SHOULDER SPINES

[Tetanurae@aol.com]

Thescelosaurus wrote:
<<    1.  What stegosaurians are known to have had shoulder spines?  The
 genera I know of are *Huayangosaurus*, *Kentrosaurus*, *Lexovisaurus*,
 and *Tuojiangosaurus*.>>

In my wanderings with these guys, I have come to the conclusion that shoulder 
spines are probably primitive for stegosaurs, and probably maybe even 
thyreophorans as a whole, the only stegosaur that seems not to have had them 
is Stegosaurus itself, and maybe Wuerhosaurus, which, conveniently clade 
exclusively with eachother based on a myriad of other characters.
 
So, to answer the question, all stegosaurs had them EXCEPT Stegosaurus and 
Wuerhosaurus.

<<    2.  What angle do the shoulder spines form with the long axis of the
 body when seen in dorsal view, if known?>>

Um...  The base is at a 45 degree angle roughly to the long axis of the 
spine, so they could theoretically spin around on the base and point any 
direction.  There may be some taphonomic information in either the papers 
that describe Tuojiangosaurus and/or Huayangosaurus, but seeing as I don't 
speak or read chinese....
 
<<    3.  Has it been shown fairly conclusively that these spines pointed
 rearward as well as laterally?>>

See #2
 
 <<   4.  Going along with #3, are these spines something likely to have
 been seriously displaced after death, like flipped in the reverse
 direction of their natural orientation?>>

Tough question.  The spines were flat based and strictly a dermal bone (ie 
not attched via ligaments etc to any other bones) that was sitting in skin 
fat and muscle, so theoretically, I could very well imagine them not ending 
up where they belonged.  Hey, this is why Kentrosaurus' spines were thought 
to have been protruding from the hips for 60 years.
 
<<5.  What would be the benefit for *Stegosaurus* to lose these spines?>>

I don't know.  Sexier? Lighter?  We need a lot more stegosaur remains to even 
have a glimpse of a picture of their evolution.
 
 <<6. Could these spines have been for display purposes instead of or in
 addition to defense?  >>

Yes.

Peter Buchholz
Tetanurae@aol.com