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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.                                   
tholtz@geochange.er.usgs.gov
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
U.S.A.