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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". ;-)
Pacific Lutheran University