The pre-thagomizer bits of stegosaurs

[rowe@lepomis.psych.upenn.edu (Mickey Rowe)]

Blaise Considine repeats his question:

> I was wondering whether the spikey forms came 1st, and evolved into
> the plated forms, whether they occurred at the same time, or what?

Last January Tom Holtz wrote the following in response to a question
about the number of tail spikes on stegosaurs (although I haven't
double-checked, I believe it was the first time that "thagomizer" was
used on this list):

  There is a debate as to whether all species of Stegosaurus had four
  spines (as in S. stenops).  Ancestrally, all stegosaurid plates were
  spines, and they became progressively more plate-like front-to-back
  over time.  It is likely that more primitive species of Stegosaurus
  may have had four or more pairs.
  
  Also, we now know that the spikes of Stegosaurus (the "thagomizer")
  were directed horizontally outwards and backwards, not upwards (as
  has been thought for 120 years).

Hope that helps.

> what are people's opinions regarding the hind-leg balancing poses
> sauropods seem to frequently be posed in today (JP's Brachiosaurus,
> AMNH's Barosaurus, pictures in several books)?

For what it's worth, my feeling is that we don't really know enough
about how they managed to appropriately regulate their blood pressure
under normal conditions to really make convincing arguments about
whether or not they could regulate it while performing such extreme
movements.  I like the Barosaurus mount at AMNH, but whether or not
it's possible? <shrug>  For a discussion, you might want to try to
find a copy of:

 AUTHOR(S):      Norell, Mark.
 TITLE:          Barosaurus on Central Park West.
 
 SOURCE:         Natural History 36-41 Dec '91

If you can't get it via interlibrary loan :-) then you might want to
try to purchase that back issue from the museum.  Whatever the cost
is, it's probably worth it just for the picture on the cover.  There
are other articles in that issue as well, including one by Peter
Dodson.  A good issue to have in your collection.  

Getting back to the question, Mark Norell writes this of the
Barosaurus mount at AMNH (I'm quoting from the abstract as it appears
in the Wilson Indexes which I can search from here.  I can do so only
because I'm affiliated with Penn so don't ask how you can do it...):

   Paleontologists are uncertain as to whether the scene depicted is
   an accurate reflection of how dinosaurs behaved.

That probably sums it up as well as anyone can.

-- 
Mickey Rowe     (rowe@lepomis.psych.upenn.edu)