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Hesperosaurus (North American Museum of Ancient Life)


Hesperosaurus (Greek for "western lizard"); pronounced HESS-per-oh-SORE-us


Woodlands of North America

Historical Period:

Late Jurassic (150 million years ago)

Size and Weight:

About 20 feet long and one ton



Distinguishing Characteristics:

Short, wide head; oval-shaped plates


About Hesperosaurus:

Stegosaurs--the spiked, plated dinosaurs--first appeared in Asia during the middle to late Jurassic period, then crossed over to North America a few million years later. That would explain the relatively evolved appearance of one of the first North American stegosaurs, Hesperosaurus, with its wide, round, mushroom-shaped dorsal plates and unusually short and blunt head (earlier stegosaurs had narrower skulls and less ornate plates). Ironically, the near-complete skeleton of Hesperosaurus was discovered in 1985 during the excavation of a fossil of its much more famous cousin, Stegosaurus.

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