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Re: The dino-bird connection revisited



>These questions combine cladistics and BADD/BCF (oh no!).
>
>Among archosaurs, did birds originate the kinetic skull (the front of the 
>skull can be bent upward)?

Although some have tried to identify kinetic structures in the crania of
nonavian theropods, they do not unambiguously possess the detailed
structures found in birds.

>Does _Protoavis_ really have a kinetic skull?  (Chatterjee says yes.  Is 
>that a part of his analysis that is in question?)

ALL of the analysis is in question, as the "monophyly" of the specimen has
not been established.  The braincase looks theropodan (even coelurosaurian),
but the reconstruction of the rest of the skull is questionable (to be
polite).

>Does _Archeopteryx_ have a kinetic skull?  (I think not--yes?)

Some have tried to identify these features (paper in the Archaeopteryx
conference volume; can't recall the authors right now). They do seem to be
there, at least incipiently.

>If _Protoavis_ did, and _Archeopteryx_ did not, might that suggest that 
>_Archeopteryx_ is a flying theropod rather than a flying bird?  That 
>would surely explain why _Archeopteryx_ plots out very close to 
>theropods.

It might if a) Protoavis was found to be a real organism, and not a chimera;
b) in a phylogenetic analysis, Protoavis was found to cluster with true
birds; c) in the same analysis, Archaeopteryx was found NOT to cluster with
birds (and presumably would be clustering with Dromaeosauridae).

However, your last sentence does not read correctly.  Archaeopteryx does not
plot out "close to theropods"; it plots out DEEPLY NESTED within
coelurosaurian tetanurine theropods.  In the same analyses, however, it
shares more derived features with modern birds than it does with nonavian
dinosaurs.  Thus, the last sentence should read that "Archaeopteryx plots
out close to birds": not a surprising thing, after all.

>What is a bird, really?  Can skeletal features provide a 
>characterization, since feathers normally won't be preserved?  I mean 
>without assuming a particular phylogeny first, since I'm not sure we know 
>whether BCF or BADD.

Depends on whether you choose anatomical or phylogenetic definitions of
taxa.  If by "birds" you mean 'Aves', then some definitions include "all
descendants of the most recent common ancestor of ratites and neognaths"
(Gauthier, 1986) or "all descendants of the most recent common ancestor of
Archaeopteryx and modern birds" (used by Chiappe).  As Olshevsky will surely
point out in his response, his formulation of Aves includes many forms not
traditionally called "birds".

>Of course, if we assume that _Archeopteryx_ is a bird, that really stacks 
>the deck in favor of maniraptoran ancestors for birds.  What should I 
>know that would show me why the claim of theropod ancestry for birds is 
>not this transparently circular?

If Archaeopteryx is not included in these analyses, it doesn't necessarily
rip out the structure.  As has long been established, birds and the
traditional dinosaurs (especially theropods) uniquely share many features of
the pelvis, hindlimb, feet, pneumatic structures, tails, necks, etc.
Archaeopteryx nicely preserves a mosaic of primitive and derived characters,
and is known from many great specimens, which is why it is central to many
phylogenetic studies.  If, however, we were to use Sinornis, Iberomesornis,
Cathyornis, and other Mesozoic birds but excluded Archie, these derived
features would still be there.

Furthermore, Archaeopteryx doesn't "stack the deck" for the maniraptoran
position of birds.  Several paleontologists (including some on this net)
have reconstructed phylogenies where traditionally nonavian theropod groups
(troodontids, oviraptorids, etc.) occupy a position closer to modern
Neornithes than does Archaeopteryx.

Where do you see the circularity here?  Archaeopteryx shares derived
features with modern birds, although it lacks many advanced features of
later birds.  It has long been considered a bird because of this (and more
recently, because the most parsimonious distribution of these characters
place it closer to unambiguous birds than to all/most "theropods").

Thomas R. Holtz, Jr.
Vertebrate Paleontologist
Dept. of Geology
University of Maryland
College Park, MD  20742
Email:Thomas_R_HOLTZ@umail.umd.edu (th81)
Fax: 301-314-9661
Phone:301-405-4084