What Is and Is Not a Dinosaur?

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A key evolutionary innovation of dinosaurs is that they walk with a fully erect posture, holding their hind legs vertically under their hips. What else makes a dinosaur a dinosaur? Learn how scientists define this group of reptiles in the first video from the AMNH.tv series "Dinosaurs Explained."

Visit AMNH.tv for more from the "Dinosaurs Explained" series.

Tags: Dinosaurs