Stegosaurus

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Lived 152 to 145 million years ago.

Stegosaurus is the classic plated dinosaur most people picture: large back plates, a small head, and a spiked tail used for defense. It lived late in the Jurassic, especially in what is now the western United States, and is best known from the Morrison Formation. This is the famous, fully recognizable stegosaur of popular imagination — the polished, later form of a branch that had already been evolving for quite some time.

We’re pretty sure Stegosaurus plates stood upright; the real debate now is their exact arrangement, not whether they lay flat.

The last stegosaurs went extinct in the Early Cretaceous, likely around 130 million years ago, probably due to gradual ecological change rather than a single extinction event.

Here's the key idea. Stegosaurus is the classic plated dinosaur most people picture: large back plates, a small head, and a spiked tail used for defense. It lived late in the Jurassic.

Finally, the core takeaway. Stegosaurus is the classic late Jurassic stegosaur — the famous plated dinosaur with a spiked tail. By the time it appeared in the Morrison Formation of the western United States, the stegosaur branch had already been evolving for millions of years, making Stegosaurus a later, polished form of a much older dinosaur design.

The flashcard inspired by it is this.

Front: What famous rock formation is Stegosaurus best known from in the western United States?

Back: Morrison Formation