SECOND THOUGHTS ON THE BIRDINESS OF THE ALVAREZSAURIDAE

[Tetanurae@aol.com]

Hello all,

Upon preparing an article on _Unenlagia comahuensis_ for an upcoming issue of
Dinosaur Discoveries I was struck by some of the features in _U_'s pelvis
that Novas uses to demonstrate that _U_ is an 'intermediate' between
dromaeosaurs and _Archaeopteryx_ + other birds.  Among these are:

Loss of the cranial portion of the pubic boot.  This makes the pubis look
more or less like a J and is seen in _Unenlagia_, _Archaeopteryx_,
"Linsterosaurus", the flying raptor, most other birds more or less, and
(surprisingly enough) _Adasaurus_.  The cranial portion is retained
primitively in Dromaeosaurs (and other non-avialaean tetanurans) and
Alvarezsaurs (or _Patagonykus_ at least)

Presence of the proximodorsal process of the ischium.  This is a tiny knob
near the suture with the illium.  It is present in _Unenlagia_,
_Archaeopteryx_, the flying raptor (I think), all other birds.  I am unaware
of the condition in "Linsterosaurus", and there appears to be the beginnings
of this in _Adasaurus_, though that could just be shading...  It is absent in
dromaeosaurs (and other non-avialaean tetanurans), and Alvarezsaurs.

Anyways, those two characters would leave me to believe that Alvarezsaurids
aren't Avialaeans at all.  BUT, Chiappe claims that they have a new skull of
the Alvarezsaurid _Mononykus_ that has supposedly lost the Jugal-Postorbital
bar, which is a bird feature, which would make me reconsider my
reconsideration....  Yet, it is also claimed that _Avimimus_ had lost this
bar, but the pieces are broke and I am pretty skeptical of the claim.  For
me, I think _Avimimus_ (the head at least) is an oviraptorosaur.

Anyways, to conclude, I am not to sure of what to make of Alvarezsaurs
anymore....  That is why I focus on ornithischians gosh darn it!

Peter Buchholz
Tetanurae@aol.com

That reminds me....... Can I become the Queen of Brazil now?

-------------------------------
REFS:

Chiappe, L M.  1995.  The first 85 million years of avian evolution.  Nature
378:349-355.

Kurzanov, S M.  1985.  The skull structure of the dinosaur _Avimimus_.
 Paleontological Journal 4:92-99.

Novas, F E.  1997.  Anatomy of _Patagonykus purtai_ (Theropoda, Avialae,
Alvarezsauridae) from the Late Cretaceous of Patagonia.  JVP 17(1):137-166.

Novas, F E, and Puerta P F.  1997.  New evidence concerning avian origins
from the Late Cretaceous of Patagonia.  Nature 387:390-392.

Sampson, S D, Krause, D W, and Forster, C A.  1997.  Madagascar's buried
treasure.  Natural History 3/97:24-27.