RE: Giant birds

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> Raymond Ancog
> I'm surprised at this. I would expect that troodontids + deinonychosaurs
> would be the sister group to Avialae, and then oviraptors and
> ornithomimids
> would be successive sister groups to the crown clade (based strictly on
> what I've read, not on first-hand information).

Sereno and Makovicky & Sues do find a troodontid + dromaeosaurid clade in
their analyses; however, I do not: troodontids come out as the sister taxon
to Ornithomimosauria OR the sister taxon to dromaeosaurids + birds.  Xu et
al. (the _Sinornithosaurus_ paper) find the latter position, too.  At the
Ostrom Symposium Norell presented an analysis by the AMNH staff: they found
troodontids as the sister taxon to oviraptorosaurs + therizinosauroids
(which is only one step longer than my most parsimonious trees in my
analysis).

Or, as I've said to various people: troodontids suck!  (at least
phylogenetically: have nothing against them personally...).

> Doesn't the
> enlarged second
> toe unite them to the exclusion of birds?

Actually, primitive birds (_Rahonavis_, for example) have an enlarged second
toe, and many primitive birds (_Rahonavis_, _Archaeopteryx_, some
enantiornithines) show hyperextensibility of pedal digit II.

> BTW, which is more acceptable, dromaeosaur or deinonychosaurs?

Both are acceptable: they represent different taxa.  Dromaeosauridae is the
clade comprised of all descendants of the most recent common ancestor of
_Dromaeosaurus_ and _Velociraptor_; Deinonychosauria is the clade of all
taxa closer to _Deinonychus_ than to Neornithes.  Under the Makovicky & Sues
or Sereno cladograms, troodontids are deinonychosaurs but not
dromaeosaurids; under the AMNH, Holtz, or Xu et al. cladograms the only
known deinonychosaurs are dromaeosaurids.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
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