Hypothesis: degrees of mesopuby

["Ken Kinman" <kinman@hotmail.com>]

Dear All,
    In my opinion, the conclusion that opisthopuby is primitive for 
maniraptorans is erroneous.  I believe the primitive state in early 
coelurosaurs was somewhat (moderately to slightly) propubic, and that this 
continued right on up to the maniraptoriform level and into the primitive 
maniraptors (early troodonts, Achillobator, etc.).   Even at the Rahonavis 
and Archaeopteryx stage, it was just barely starting to shift to the 
opisthopubic side of mesopuby.
     The major exceptions are the segnosaurians who needed increasing 
opisthopuby for an expanding gut, and then one or more clades of 
dromaeosaurs also evolved in a more opisthopubic direction for reasons that 
are not clear.  I think that Sinovenator is one of those dromaeosaur clades 
(perhaps with Sinornithosaurus?).
     After we get past Archaeopteryx, opisthopuby is the rule rather than 
the exception.  Why oviraptors reversed back to a more propubic is anyone's 
guess, but I think it is the only major reversal of this kind.
    If Sinovenator is a basal troodontid, then this same kind of reversal 
must have happened, but I think this is unnecessarily unparsimonious.  I 
believe the basal troodonts would be similar to Sinovenator, but with a 
mesopubic or even slightly propubic orientation.
    Of course I have looked at lots and lots of other characters in coming 
to this conclusion, but that's the way it looks to me.  The earliest Aves 
(sensu lato), such as early troodonts would have only recently evolved fused 
distal carpals (true semilunates), and would probably have unfused distal 
carpals until very late in ontogeny.  At the Deinonychus stage you might 
have to go earlier into ontogeny to find an unfused semilunate (such as that 
juvenile Deinonychus---at Yale? or Harvard?).
   Well, that's all the time I have for now.  If I don't get "constructive" 
criticism on this, and just get "peanuts" or worse thrown at me, I will 
probably go into a more extended period of lurking.  We shall see.
         ------- Cheers,  Ken


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