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Re: ABELISAURIDS & CARCHARODONTOSAURIDS



On Mon, 15 Mar 1999 darren.naish@port.ac.uk 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 
> carcharodontosaurids. 

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
_T. rex_.

Nick Pharris
Pacific Lutheran University
Tacoma, WA 98447
(253)535-7045