RE: Aussie alvarezsaur? (was Re: Gondwanan Dinosaurs)

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

> Jaime A. Headden wrote:
>
> >   *Rapator ornitholestoides*:
> >
> >   I'll not say too much on this bone, but it bears
> >similarities to some Asian taxa which suggests it's
> >not a mcI to begin with, but a dI-1, like mononykids,
>
> This is a very good observation.  In alvarezsaurids, phalanx I-1 (the one
> that bears the big hand-claw) is very long anteroposteriorly but
> compressed
> lateromedially, giving it a distinctive "hourglass-like" shape.
> So is the
> "metacarpal" of _Rapator_ (BMNH R3178).
>
> Phalanx I-1 of alvarezsaurids also shows (1) an elongated posteromedial
> process (quite hook-like in _Patagonykus_, less so in mononykines); (2)
> bilobed proximal end, giving it a "B-shaped" articular surface; (3) deep
> extensor ligament pit; and (4) a symmetrical distal ginglymus.
> Judging from
> Huene's figures (reproduced in Glut), characters (1), (2) and
> possibly (3)
> are seen in _Rapator_.  I'm not sure about (4).
>

Ah, well...

Kudos to Jaime.  As part of a revision of basal tetanurines, I came across
the same observations.  I asked a couple of other theropod guys to check on
it: they seemed very favorable to this hypothesis.

So, although we haven't got the publication out yet where we discuss it, I
am EXTREMELY favorable to the idea of _Rapator_ possibly being phalanx 1 of
manual digit I of a (large) alvarezsaur.


                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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