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Re: Hypothesis: degrees of mesopuby



In a message dated 2/15/02 6:26:37 PM Eastern Standard Time, 
kinman@hotmail.com writes:

>      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.).   

Um, the next most basal well-known troodontid (after _Sinovenator_) is 
_Sinornithoides_, which is mesopubic.

Opisthopubic > mesopubic > very slightly propubic, with a concomitant 
(related?) increase in body size--exactly the same as what happened in 
oviraptorosaurs and large dromaeosaurs.  Makes sense to me.


>  Even at the Rahonavis 
>  and Archaeopteryx stage, it was just barely starting to shift to the 
>  opisthopubic side of mesopuby.

Either that, or that's where it began, with developments in various lineages 
leading towards either extreme opisthopuby, continued mesopuby, or slight 
propuby.


>        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.

_Achillobator_?  Or is this not a "major" reversal?

>  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.

[eyes boggle; the water I have just drunk shoots out of my mouth Danny 
Thomas-style]

Huh???  Non sequitur.  The fusion of the slc (whatever that ends up meaning) 
could easily have been a single mutation, possibly one that caused the wrist 
cartilages to fuse before they ever even ossified.  Ontogeny doesn't *have* 
to recapitulate phylogeny.

--Nick P.