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Incisivosaurus gauthieri



This is a good week for dinosaurs!!

In today's Nature: the basal oviraptorosaur Incisivosaurus gauthieri, in the
following paper:

XU, X., Y.-N. CHENG, X.-L. WANG & C.-H. CHANG. 2002. An unusual
oviraptorosaurian dinosaur from China. Nature 419, 291 - 293.

It is known from a skull and a cervical, from the (fluvial) base of the
Yixian, like Sinovenator, Liaoceratops, and... other things that you'll be
hearing about over the next year.  Skull length is about 10 cm (4").  It
looks for all the world like what one would get if you used a graphics
package to "morph" the skulls of Erlikosaurus and Caudipteryx, and probably
not without reason...

The name refers to the prominent incisiform premaxillary teeth and Jacques
Gauthier.  This specimen has the most complete dentition of any
oviraptorosaurian: premaxillaries in the front of the premax, and
therizinosaur-like maxillary and dentary teeth *with wear facets*.

This is the specimen that essentially drives the nail in the coffin of the
avialian status of Oviraptorosauria, at least as based on cranial
morphology.  It shares with "classic" oviraptorosaurs (or more broadly with
other "enigmosaurs") a short preorbital region of the skull, big
premaxillary main body, dorsally positioned external naris (also in birds),
pendant paroccipital process, vertically oriented ectopterygoid, fused
dentary symphysis, long and shallow posteroventral process of the dentary,
strap-like splenial, large mandibular fenestra, and long retroarticular
process.  However, it lacks the following features previously used to link
oviraptorosaurs and dervied avialians: toothless jaws, short nasals, long
parietals, quadrate with a lateral cotyle for the quadratojugal, rodlike
jugal bar, long maxillary process of the palatine, absence of a subsidiary
palatine fenestra, ectopterygoid that articulates primarily with the
lacrimal and maxilla laterally, absence of a jugal hook on the
ectopterygoid.  In nearly all these cases it resembles therizinosauroids
rather than birds.

So perhaps oviraptorosaurs are secondarily flightless, but there is far less
support now that they would have branched off from the bird line after
Archaeopteryx did (rather than before: the "standard model").

Xu et al.'s phylogenetic study puts it in the basalmost position of
Oviraptorosauria, below Caudipteryx + the Oviraptoroidea polytomy.  I've
input it into my current version of the matrix, and find the same.

                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
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796