Re: Albertosaurinids

[pharrinj@PLU.edu]

On Sat, 6 Jan 1996 Dinogeorge@aol.com wrote:

> 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.
> 

I'm saying that a narrow beak (like that seen in troodonts) is a 
primitive feature, where other tyrannosaurs broadened their snouts as 
they got big and developed new hunting techniques.  It could also be a 
parallel development, as in the albertosaurine _Daspletosaurus_.  
Outgroups to tyrannosaurs (troodonts, 
ornithomimids, birds, archaeopterygids, dromaeosaurs) have no lacrimal 
horns, and other primitive tyrannosaurs (_Alectrosaurus_, _Alioramus_) 
don't either (at least that's my interpretation, given the scrappy nature 
of the skulls of the latter two taxa).  OK, to be completely honest, I 
have to concede the existence of a lacrimal horn in _Pelecanimimus 
polyodon_, but it's very small.

Character polarity is important in such discussions.

BTW, you've stuck two separate endings on the ends of words like 
"albertosaurinid".  I assume you mean "albertosaurine".  ;-)

     See ya,

     Nick Pharris
     Pacific Lutheran University