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Re: The Enigma of Psittacosaurus

----- Original Message -----
From: "Steve Brusatte" <dinoland@lycos.com>
To: <dinosaur@usc.edu>
Sent: Thursday, July 11, 2002 12:34 AM
Subject: Re: The Enigma of Psittacosaurus

> Alessandro wrote:
>>I think that the usage of laterally projecting jugal horn is a generalized
>>character for Psittacosaurus species, infact within Psittacosaurus the
>>horn is highly varibale, in most species the jugal horns point backward
>>the skull in dorsal view, nevertheless P. sinensis and P. xinjiangensis
>>jugal horn that point almost forward and the rostral edge is nearly
>>perpendicular to the skull mid-line. P. meileyingensis has small jugal
>>while P. neimongoliensis and P. youngi have larger jugal horn directed
>>backward. P. ordosensis has fairly large jugal horns also directed
>>P. mongoliensis has long jugal horns directed laterally.

>Right.  I would say the presence of said jugal horn is a generalized
>character for _Psittacosaurus_.  It's the position and development of that
>horn that makes it one of the few, IMHO, solid potential synapomorphies
>that can be used to discern interrelationships.  _P. sinensis_ and _P.
>xinjiangensis_ do have the extended jugal horns that extend far to the
>side.  As far as I can tell from illustrations, _P. meileyingensis_ does
>have a small horn.  _P. youngi_ also appears to have a somewhat large jugal
>horn.  The horns of _P. mongoliensis_ also point to the side, although its
>lateral point is directed somewhat backward (more so than in _P.

And what about the partecipation of the frontal in the supratemporal fossa?
In P. sinensis, and P. youngi the partecipation of the frontal in the
formation of supratemporal fossa is present, while in P. mongoliensis, P.
neimongoliensis, P. meileyingensis the frontal don't partecipate, in
outgroups as Neoceratopsian the condition is that the partecipation is
present, this is the case also in the very primitive Neoceratopsian
Liaoceratops yanzigouensis, and Archaeoceratops oshimai, and also in
Lesothosaurus diagnosticus (used by me as outgroups), I've used
Archaeoceratops because the condition in Chaoyangsaurus youngi is unknown,
unfortunately the condition is unknown also in P. xinjiangensis and P.

Alessandro Marisa
Via Achille Grandi n°18
Rovereto (TN) ITALY
Tel: 039-0464-434658 Email: amaris@tin.it