Types of dinosaurs. Dinosaurs are united by at least 21 traits in their skulls and skeletons. These common characters (called synapomorphies) are the reason palaeontologists are sure dinosaurs had a common origin. However, when definite dinosaur fossils appear (early in the Upper Triassic), the group had already split into two great orders, the Saurischia, and the Ornithischia.Dalianraptor is listed by Olshevsky, but omitted from this list, since it has not been described as a nonavian dinosaur in a published source. ↑ Tereschenko, VS Alifanov, VR (2003). Bainoceratops efremovi, a new protoceratopid dinosaur (Protoceratopidae, Neoceratopsia) from the BainDzak Locality (South Mongolia).
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