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Re: ABELISAURIDS & CARCHARODONTOSAURIDS
On Mon, 15 Mar 1999 firstname.lastname@example.org wrote:
> Rugosity of the dorsal
> surface of the nasals, invasion of the orbit by a rostral process of
> the postorbital bar and I think rugosity on the dorsal surface of the
> postorbital are some of the characters that have been advanced in
> favour of this relationship: all are seen in both abelisaurids and
I believe Phil Currie also uses contact between the postorbital and
lacrimal, which is present in abelisaurids and carcharodontosaurs and
almost present in _Sinraptor_ (which Currie also assigns to this group).
However, since this contact is not fully developed in _Sinraptor_, then if
it is really synapomorphic in abelis and carchs, then that makes
_Sinraptor_ the sister group to (Abelisauridae + Carcharodontosauridae).
This seems to be going a bit far to me, considering the large number of
cranial and postcranial characters allying _Sinraptor_ to the allosaurids
(and allying _Acrocanthosaurus_, which Currie excludes from this group,
both to allosaurids and to other carcharodontosaurs).
> Aublysodonts and tyrannosaurines like _Gorgosaurus libratus_ also
> show that the tyrannosaurid orbit is not, ancestrally, invaded by
> the postorbital process in tyrannosaurids, yet this condition seems
> to have convergently evolved in _Tyrannosaurus_ and _'Albertosaurus'
> arctunguis_ (though this might be arguable - please comment if so).
The postorbital apparently does not invade the orbit in _Daspletosaurus_,
either. This may be an ontogenetic (or otherwise size-related) feature,
as the orbit is also not invaded in _Nanotyrannus_, which may be a young
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