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Re: Dinosaur Questions (last)

> > Why was Protoceratops classified as a ceratopsian?
>The simple answer: it has the beginnings of a neck frill, a similar
>beaked jaw, and a similar leg structure.  No other group of dinosaurs
>has quite this combination of characters.
>The complex answer is a long list of details of the skeleton which
>are the same between Protoceratops and the other ceratopsians, but
>are different than the details seen in other groups of dinosaurs.
>[Such as the relative size and shape of certain bones, and so on].

One of these characters is the rostral bone - a special extra bone at the
end of the beak, in front of the premaxillae.  Only ceratopsians (from
Psittacosaurus to Triceratops) have them.

Thomas R. Holtz, Jr.                                   
Vertebrate Paleontologist in Exile                  Phone:      703-648-5280
U.S. Geological Survey                                FAX:      703-648-5420
Branch of Paleontology & Stratigraphy
MS 970 National Center
Reston, VA  22092