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true semilunates & carpometacarpi (was Caenagnathiformes)
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
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
---- 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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