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RE: Question on Anchiornis huxleyi

> From: owner-VRTPALEO@usc.edu [mailto:owner-VRTPALEO@usc.edu] On Behalf Of Leo 
> W Sham
> Sent: Thursday, June 20, 2013 2:23 AM
> To: VRTPALEO@usc.edu; dinosaur@usc.edu
> Subject: Question on Anchiornis huxleyi
> Dear Listers,
> I am confused about the current taxonomic status of Anchiornis. What is the 
> current opinion for the questions below?
> (1) Is it considered a sister taxon/outgroup of Troodontidae, or that of 
> Avialae, or still something else e.g. basal Avialae?
> (2) It it closer than, or less close than, Archaeopteryx to crown Aves 
> (Neornithes)?
> (3) Any relevant comments?
> Thank you very much in advance! You can reply to me in private.

The main takehome messages of recent papers on basal paravians should be:
1) There is no simple single unassailable resolution of the position of 
"archaeopterygid"-grade theropods, likely because...
2) Said animals are very close to the divergence between Dromaeosauridae (in 
whatever combination), Troodontidae (ditto), and
Avialae (ditto again).
3) And as such they will continue to jump back and forth between the basal 
branches of the clades in question.

But that is okay. And actually is much more informative than a stabilized 
position. Ultimately it is far less significant to resolve
whether Archaeopteryx &/or Anchiornis &/or Aurornis &/or Xiaotingia &/or etc. 
are basal avialians or basal deinonychosaurs or so
forth. Instead we should recognize that we have very likely homed in on the 
morphotype which gave rise to both the
dromaeosaurid-line and the bird-line. Yes, it will be more helpful in the end 
to pick out which ones fit where, but if some of these
animals are on one branch and others on the other, then we have established the 
basal morphology of Paraves and the form which gave
rise to both divergent clades.

NOTE: All the above hinges on the standard model of Deinonychosauria and 
"archaeopterygids" being close to crown-group birds than
are oviraptorosaurs; the alternative model, proposed by various workers, is 
that Oviraptorosauria is closer to crown-group birds and
that archaeopterygids are just basal deinonychosaurs.

Thomas R. Holtz, Jr.
Email: tholtz@umd.edu   Phone: 301-405-4084
Office: Centreville 1216                        
Senior Lecturer, Vertebrate Paleontology
Dept. of Geology, University of Maryland
Fax: 301-314-9661               

Faculty Director, Science & Global Change Program, College Park Scholars
Fax: 301-314-9843

Mailing Address:        Thomas R. Holtz, Jr.
                        Department of Geology
                        Building 237, Room 1117
                        University of Maryland
                        College Park, MD 20742 USA