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Re: "Pinnants" (was Re: BIRDY _ARCHAEOPTERYX_)



Message text written by INTERNET:Dinogeorge@aol.com
>Unless I misread the post, the argument was using the >reversal< of the
avian
foot into the arctometatarsalian condition as something very unlikely to
happen. My point was that this is the same kind of transformation that must
take place in the theropod foot to make it segnosaurian, and that it must
surely, therefore, be just as unlikely.<

        I think we crossed wires here somewhere (knowing me, probably on my
end!) -- apologies for the confusion!  I perceived that you were saying
that the segnosaurian foot (with four completely unfused metatarsals) would
have to have undergone a marked reversal (from an arctometatarsalian
condition...???) to explain its pedal morphology in light of the
phylogenetic analyses that place the group deeply nested within the
Theropoda -- this was in response to my post pointing out that in order for
enantiornithine birds to be descended from a theropod possessing an
arctometatarsus would likewise require a reversal.  What I was trying to
say was that if the arctometatarsalian condition arose independently in
several advanced lineages of theropods (which it seems to have done -- once
in alvarezsaurids, once in caenagnathids, and again in the
Tyrannosauridae+Bullatosauria group), then, by default, the closest common
ancestor of _all_ these theropods would have to have an unfused, un-
arctometatarsalian pedal morphology.  Segnosaurs certainly could still be
in this group (as they seem to be, based on the braincase morphology); they
just weren't one of those groups that ever evolved the arctometatarsalian
pedal morphology.  Did that help?



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                     Jerry D. Harris
                 Fossil Preparation Lab
          New Mexico Museum of Natural History
                   1801 Mountain Rd NW
               Albuquerque  NM  87104-1375
                 Phone:  (505) 899-2809
                  Fax: ; (505) 841-2866
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