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Greg Paul is not necessarily right; or "Archie may be a birdy"
I hate to pick on Tom again, but in 2009 I wrote a DML post responding to his
announcement of Tawa which he titled "Everything you know about basal
saurischians is wrong." You can read it here-
http://dml.cmnh.org/2009Dec/msg00122.html . Tawa's analysis shook up theropod
phylogeny by finding paraphyletic coelophysoids (even sensu stricto), but since
then we've had the Eodromaeus analysis which found coelophysoids to be
monophyletic and include Tawa itself. That's not to say the Eodromaeus
analysis is right, but that Tawa does not definitely change what we know about
theropod relationships. The point of my post was that each new analysis does
not prove the last analysis wrong, and it bears repeating for the current
thread on Xiaotingia.
Xu et al. placed Xiaotingia in Senter's (2007) version of the TWG matrix with
13 added characters and a few added taxa. Archaeopteryx emerged as a basal
deinonychosaur, but the abstract itself says this has only "tentative
statistical support" and is rightly conservative regarding its implications.
While Senter's analysis is great, and Xu et al. (and Hu et al., 2009 and Zheng
et al., 2008) were smart to add Anchiornis, Epidexipteryx, Similicaudipteryx
and Haplocheirus, there are numerous relevant taxa not included. The basal
dromaeosaurids Mahakala, Shanag and Tianyuraptor, the basal troodontids
Jinfengopteryx and Sinusonasus, the basal birds Jixiangornis, Dalianraptor,
Yandangornis and Zhongjianornis, the unenlagiine Austroraptor, the early
paravian Pedopenna, and the controversial Balaur are some of the most
important. There are also plenty of characters not included, as most of the
taxa I just listed came with versions of the TWG matrix that added their own
list of additional characters for paravian nodes (e.g. 37 new characters for Xu
et al.'s Anchiornis paper, 56 new ones in Xu and Zhang's Pedopenna paper). So
while the Xiaotingia results are certainly interesting, they're by not
necessarily better than the results from the papers describing Mahakala,
Shanag, Tianyuraptor, Austroraptor, Pedopenna or Xu et al.'s Anchiornis paper.
Maybe any combination of these taxa or characters is integral to keeping
Archaeopteryx in Avialae, regardless of the inclusion of Xiaotingia. We won't
know until all the data is combined (which I'm doing for the upcoming
publication of yet another important basal paravian). Until then, I'd say any
paravian topology is likely. Recall that correcting the original TWG matrix
led to Archaeopteryx being removed from Avialae in just three extra steps and
being a troodontid with four more steps. It's not a hard taxon to shift around.
> Date: Wed, 27 Jul 2011 13:20:13 -0400
> From: firstname.lastname@example.org
> To: email@example.com
> Subject: Greg Paul is right (again); or "Archie's not a birdy"
> Been very hard to keep quiet about this one for oh these looooonnnnnggggg
> An Archaeopteryx-like theropod from China and the origin of Avialae
> Xing Xu, Hailu You, Kai Du & Fenglu Han
> Nature 475, 465–470 (28 July 2011) doi:10.1038/nature10288
> Received 16 November 2010 Accepted 10 June 2011 Published online 27 July 2011
> Archaeopteryx is widely accepted as being the most basal bird, and
> accordingly it is regarded as central to understanding avialan origins;
> however, recent discoveries of derived maniraptorans have weakened the
> avialan status of Archaeopteryx. Here we report a new Archaeopteryx-like
> theropod from China. This find further demonstrates that many features
> formerly regarded as being diagnostic of Avialae, including long and
> robust forelimbs, actually characterize the more inclusive group Paraves
> (composed of the avialans and the deinonychosaurs). Notably, adding the
> new taxon into a comprehensive phylogenetic analysis shifts Archaeopteryx
> to the Deinonychosauria. Despite only tentative statistical support, this
> result challenges the centrality of Archaeopteryx in the transition to
> birds. If this new phylogenetic hypothesis can be confirmed by further
> investigation, current assumptions regarding the avialan ancestral
> condition will need to be re-evaluated.
> Larry Witmer's News & Views:
> Various media reports:
> Basic gist of story: discovery of (yet another boring generic-looking)
> feathered paravian from China that, when included in a phylogenetic
> matrix. pulls Anchiornis and Archaeopteryx together with itself to form
> Archaeopterygidae, and Archaeopterygidae pulled over as basal
> deinonychosaurs rather than avialians.
> (Hence the Greg Paul comment: Greg and Ken Carpenter had argued as early
> as the mid-1980s that Archaeopteryx was a basal member of the
> Dromaeosauridae-line rather than the bird line.)
> Statistical support for this position is not tremendously strong, so this
> is by no means written in stone. (Indeed I know of at least one study
> coming soon which will turn all of this inside out: however, that paper
> lacks the Xiaotingia zhengi data).
> Cool stuff.
> Thomas R. Holtz, Jr.
> Email: firstname.lastname@example.org 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