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>>This makes me wonder if similar displays would have been used by Theropods.
>>appears that fights only occur when a "winner" and a "loser" cannot be 
>>determined through "bobbing". 
>Sure, theropods could well have exhibited this kind of behavior. (But how
>could we confirm this?)

Obviously, we can't confirm this in nonavian theropods.  However, it is
expected in all dinosaurs on phylogenetic grounds.

Both lepidosaurs and birds use head-bobbing in intraspecific display.  This
is probably a basal diapsid behavior, so the expectation is that, unless
they lost this behavior for some reason, extinct diapsids used head-bobbing
as well.

Of course, there is the question of crocodiles.  Do they use head-bobbing?
If not, either they lost that feature or the behavior evolved independantly
in lepidosaurs and birds.

Thomas R. Holtz, Jr.
Vertebrate Paleontologist
Dept. of Geology
University of Maryland
College Park, MD  20742
Email:Thomas_R_HOLTZ@umail.umd.edu (th81)
Fax: 301-314-9661