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> Arctometatarsialian has been used about 500 times, but could
>somebody please define it? And did those cladograms actually put T. rex
>closer to modern birds than Archaeopteryx, or was I misreading that?
Arctus (L. compressed, channeled, pinched). Nothing to do with arktos (Gr.
bear, and the related term artikos, land of the bear (i.e., the North)).
The arctometatarsalian condition is the pinched third metatarsal condition
seen in tyrannosaurids, ornithomimids, troodontids,
elmisaurids/caenagnathids, Avimimus, and Mononykus (but NOT in
Archaeopteryx, ornithurine or enantiornithine birds, etc.). If you have
access to pictures of the foot of Struthiomimus or Albertosaurs, they will
show this. (Sadly, almost every T. rex specimen mounted is mounted with the
wrong sort of foot!)
Tony Thulborn and a certain poster to the net from out in Washington State
have found the position you describe, but (important emphasis) NO computer
generated cladogram has found the same.
In the various phylogenies I've cooked up, true Arctometatarsalia (including
at least Tyrannosauridae, Troodontidae, and Ornithomimosauria) is less
closely related to birds than are Archaeopteryx or the Dromaeosauridae. In
my most recent studies, oviraptorosaurs and therizinosauroids were also
closer to birds than are the arctomets.
A similar position has been found by the AMNH workers (Clark, Norell,
Chiappe, Perle, etc.), with therizinosauroids among the arctomets (well, if
they are going to reverse the foot, they might as well do it all the way!).
Sereno still finds a monophyletic Deinonychosauria as the sister group to
birds, with tyrannosaurids further out, and an
ornithomimosaur-therizinosauroid clade further out than that.
Currie finds birds within Arctometatarsalia (maybe closer to troodonts than
to ornithomimosaurs or tyrannosaurids), but his most recent coelurosaur
cladograms are still not publically presented (i.e., they were not shown at
the SVP theropod meeting).
Thomas R. Holtz, Jr.
Dept. of Geology
University of Maryland
College Park, MD 20742