Re: Albertosaurinids

[Dinogeorge@aol.com]

In a message dated 96-01-06 19:30:27 EST, pharrinj@PLU.edu writes:

>Well, I tend to think of _Nanotyrannus_ as more primitive than any other 
>known group of tyrannosaurs.  Its wedge-shaped skull, narrow beak, large 
>orbits, forward-pointing parasphenoid, and infratemporal fenestra without 
>any large rostral process of the quadratojugal and squamosal make it the 
>most troodont- or ornithomimid-like tyrannosaur known (i.e. the most 
>primitive).  That not all of these features are strictly size-related can 
>be seen by examining the skulls of other small tyrannosaurids (_Alioramus 
>remotus_, _Gorgosaurus sternbergi_, _Maleevosaurus novojilovi_), which 
>have broad snouts and, in particular, large rostral processes across the 
>infratemporal fenestra.

Having a widely expanded occiput relative to snout width (best seen in
ventral view in Gilmore's 1946 paper), resulting in orbits having a
forward-pointing component, seems to be a derived feature shared by
_Nanotyrannus_ in common with _Dinotyrannus_ and especially _Tyrannosaurus_.
Other putative tyrannosaurinid synapomorphies include a lacrimal with no horn
and a ventrally deflected occipital condyle.