Dinosaurs first appeared on our planet in the earliest Triassic, it is believed they descended from earlier terrestrial reptiles such as the anapsid and the diapsida. The main characteristics that dinosaurs display that makes them dinosaurs are, they all have three or more sacral vertebrae (vertebrae over the hip) (A); a rear facing shoulder joint (B); asymmetric hands with two small outer digits (C); an open hip socket ( D); a cnemial crest on their tibia (E); an ascending process on their astrgalus (F); and a sigmoidal third metatarsal (G).

Illustrations of the features mentioned above (scale bars are 10 cm).

general dinosaur anatomy

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