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New AVES definition refined (more testable?)
I would like to thank those who have given some constructive feedback
on this matter. I fully expected my proposal to be controversial (but I was
a little surprised just how strongly it is being dismissed before it is even
tested). Mickey Mortimer's upcoming analysis will be an important first
test, and *if* he can convince me that "enigmosauria" is holophyletic, I
will certainly modify my proposal accordingly.
However, I am convinced that the case for "enigmosaur" paraphyly is at
least as strong as it is for holophyly, and there may be some surprises for
those who are drawing definitive conclusions before rigorous testing is
done. Therefore, I cannot in good conscience back away from enigmosaur
paraphyly just because that possibility is being so heavily criticized.
Now, it is certainly not easy coming up with a better and more precise
redefinition of AVES until it becomes a cooperative effort, but I am
proceeding as best as I can. What follows is a more refined definition
(assuming enigmosauria will be shown to be paraphyletic after more rigorous
testing is done). I will first give my proposal for the Primary Definition,
and then follow it with a list of supportive characters I have come up with
PRIMARY DEFINITION of Class Aves sensu lato (proposed): Theropods
possessing both a "convex coracoid glenoid" AND at least one the two
following carpal characteristics: (1) Distal carpals I and II enlarged and
fused into a single element with a distinctive semilunate shape; and/or (2)
this fused structure fully caps metacarpals I and II.
Notes: Protarchaeopterx and Caudipteryx meet this definition even
though they apparently lack the distinctive semilunate "shape". Deinonychus
also meets the definition, even though one of its metacarpals is not "fully"
capped. Segnosaurians do NOT meet this definition, although Beipaiosaurus
seems to approach it the best. The segnosaurians are most likely the sister
group of Class Aves sensu lato, and therefore many of the supportive
characters which are listed below will be found in some or all segnosaurians
(as noted). Tyrannosaurs appear to be further out (contra Sereno's
(1) Enlarged sternum articulating with more than 2 pairs of ribs. Also
note that sternal anterior margin is apparently often slotted for coracoids
(and said coracoids sharply reflexed).
(2) Possession of ornithoid eggs (microstructure modified or partially
reversed in Troodontidae).
(3) Possession of vaned feathers (may occur in some outgroups including
segnosaurians). A particular kind of vaned feathers or their bodily
distribution may eventually distinguish Aves from the earlier forms
(insufficient data at present).
(4) Laterosphenoid head small, and snovial joint small or absent
(unknown if this also occurs in segnosaurians or not).
(5) Anterior trochantor splitting from greater trochantor closer to
femoral head (occurs in tyrannosaurs as well).
(6) Preacetabular blade of ilium dorsoventrally elongated (also in
segnosaurians, but it is distinctively expanded laterally).
(7) Bowed ulnar shaft (also present in some outgroup genera).
(8) Lacrimal-frontal contact present (also occurs in tyrannosaurs).
(9) Relatively large hypapophyses on anterior dorsals (also in
Neimongosaurus and Ornitholestes).
(10) Often possess ossified uncinate processes.
(11) Dorsal carpals I and II have a pronounced trochlear groove on the
proximal side (also occurs in Coelurus, segnosaurians and tyrannosaurs).
(12) Most Aves (but caenagnathiforms are primitive in this respect)
have retroversion of pubes to varying degrees (retroversion in segnosaurians
probably occurred in parallel--i.e. a mild case of convergence).
(13) The fused distal carpal element has often fused to the metacarpals
(forming a carpometacarpus). Apparently arose at least twice in Class Aves
(14) Distal end of ulna more than 1.5 times as broad as tall (this
character could probably use some refining).
(15) Anterior trochantor cylindrical (also in derived segnosaurians).
(16) Reduced supracetabular crest of ilium (also in some tyrannosaurs
(17) Several other characters I haven't had time to work on.
So there you have my viewpoint as it stands at present. If Mickey's
analysis convinces me that "enigmosauria" is holophyletic, I will modify my
proposal accordingly. However, I think even he may be surprised, and that
the case for "enigmosaur" paraphyly is a very viable alternative. According
to this alternative view, "enigmosauria" is based on plesiomorphies and
parallelisms. We shall see. As always, *constructive* comments are
------- Cheers, Ken Kinman
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