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Are alvarezsaurids arctometatarsalian?
And the answer is:
No. (Well, very probably not).
I've only had the paper for fifteen minutes, but I took a quick look through
Novas' new paper on Patagonykus.
There has been some debate on the net as to whether the clade Patagonykus +
Mononykus belongs in Arctometatarsalia, as the metatarsal condition of
Mononykus meets and surpass the pinching of mt III seen in true
Arctometatarsalia (tyrannosaurids and bullatosaurs). The condition in
Alvarezsaurus (regarded as a primitive relative of Patagonykus + Mononykus)
is non-arctometatarsalian. When word of Patagonykus first broke (okay, the
funny thing is, I actually held in my hand some of the Patagonykus material
while writing my dissertation, but that's a story for another time...),
there was debate as to whether it would have a more primitive foot (like
Alvarezsaurus) or an advanced foot (as in Mononykus).
And the winner is... A relatively primitive foot. The mt III of Patagonykus
is only pinched as much as in oviraptorosaurs or dromaeosaurs (or basal
birds), and the proximal portion reaches the ankle.
This suggests that Parvicursor and/or "Ornithomimus" minutus (if either of
them are indeed alvarezsaurids) are more closely related to Mononykus than
to either of the two Argentine forms.
Now, I've got to spend a LONG time with Witmer's antorbital monograph. Time
to recode the characters! :-)
Thomas R. Holtz, Jr.
Vertebrate Paleontologist Webpage: http://www.geol.umd.edu
Dept. of Geology Email:firstname.lastname@example.org
University of Maryland Phone:301-405-4084
College Park, MD 20742 Fax: 301-314-9661