Re: The most important fossil discovery in 2004 (your opinions?)

[Mickey Mortimer <Mickey_Mortimer111@msn.com>]

Amtoine Grant wrote-

> which makes the question "how can we be sure it is THE[of the species
> we know] basal tyrannosaurid, and not something else".

We can't, but it is more parsimonious than other hypotheses given the
published data.  Tyrannosauroid synapomorphies include- fused nasals; nasals
anteriorly convex in section; pneumatic articular; preacetabular notch in
ilium.

> Which brings to mind the allosaurs to tyrannosaurs theory. I actually
> lost my 'Predatory Dinosaurs of the World' at the airport before I got
> to that section. Uh, could someone break down or point to an article
> online where it discusses this.  Because last I checked tyrannosaurs
> were considered coelurosaurs that attained their size independent of
> the allosaurs, similar to the spinosaurids. Aren't allosaurs considered
> carnosaurs, on a serperate branch from the coelosauria?

Tyrannosauroids have been considered coelurosaurs by all(?) published
numerical phylogenetic analyses where this has been tested.  Allosaurids are
by definition carnosaurs.  Paul (2002) lists only a few features to justify
placing tyrannosauroids in Carnosauria - deep, anterodorsally directed
cultriform process; broad squamosal-quadratojugal bar; third metatarsal
L-shaped in proximal view.  These seem more likely to be avetheropod
symplesiomorphies, and are far outnumbered by the coelurosaurian characters
of tyrannosauroids.  Dilong does have a few carnosaurian characters, but it
resembles basal coelurosaurs far more.

> While we're at
> it, how does allosaur hind-limb morphology differ from tyrannosaurs in
> terms of gracility?

Allosaurids are less gracile than similarly sized tyrannosaurids.

Mickey Mortimer
Undergraduate, Earth and Space Sciences
University of Washington
The Theropod Database - http://students.washington.edu/eoraptor/Home.html