true semilunates & carpometacarpi (was Caenagnathiformes)

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

    Before commenting on Mickey Mortimer's post, let me just quickly note 
that I've come to the conclusion that Sternberg (in naming Caenagnathus) 
probably did mean "novel jaw" (as in a new type of jaw), not "recent" jaw.  
Caenagnathiformes would thus be even more appropriate (forms sharing a 
similar kind of "novel jaw").
    Now, referring to Mickey's statement below, I am glad to see no mention 
that the "true semilunate" may have arisen twice (although I am aware of 
that possibility, however remote I think it may be).  Unfused carpals in 
Segnosauriformes don't worry me too much, since I don't use the words fused 
or unfused in my definition (I did that on purpose since fused carpal 
elements occur in some primitive forms that lack true semilunates).  But it 
occurs to me that perhaps unfused "true semilunates" is another reason to 
keep Segnosauriformes in a clade separate from Caenagnathiformes (in other 
words "enigmosauria" may be paraphyletic, or at least it's holophyly still 
remains unconvincing to me).
    I'm not sure exactly what Mickey means by non-semilunate form in 
Caudipteryx and Protarchaeopteryx, but assume it is the shape.  So to 
account for that, perhaps the  definition should say: "usually" has a 
distinctive semilunate shape.  I listed the size criterion first, since the 
relatively large size seems to be a little more diagnostic than shape 
anyway.
    And now for the problem of carpometacarpi.  Since a "metornithes" clade 
is now appearing less likely, I've concluded that carpometacarpi probably 
evolved at least twice, once in pygostylians and at least once among the 
non-pygostylians ("alvarezsaurians" and Avimimidae).  There is certainly a 
question in my mind whether the latter two groups evolved it separately or 
not.  If we W4MA (wait for Mickey's analysis) perhaps that will shed some 
light on this question.
    What *does* concern me is the possibility that the fused carpals found 
in some non-maniraptors could be mistaken for one of these fused "true" 
semilunates (i.e. carpometacarpi).  Is this a potential problem (I am not 
aware of any known forms that would give us such problems at the present 
time)?
        ---- Cheers,  Ken Kinman

*****************************************
Mickey Mortimer wrote:
  Even assuming the semilunate of enigmosaurs and paravians is easily 
distinguishable from the primitive condition (which probably isn't that 
simple, given the unfused carpals in therizinosauroids, block-like fused 
carpometacarpus in alvarezsaurids, non-semilunate form in Protarchaeopteryx 
and Caudipteryx, etc.), we will undoubtedly find intermediates that make the 
presence of this state hard to judge.



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