Stegosaurus armatus


Name: Stegosaurus armatus

Age: Late Jurassic (~150 million years ago)

Where It's Found in Utah: Cleveland-Lloyd Dinosaur Quarry, Emery County, and Dinosaur National Monument, Uintah County.

Geologic Formation: Morrison Formation (Brushy Basin Member)

Classification: Ornithischia – Thyreophora – Stegosauria - Stegosauridae


Description: Stegosaurus was a 30 foot long plant-eating dinosaur that had two alternating rows of up to 17 plates running down its back and 4 tail spikes. These bones were not directly attached to the rest of the skeleton; the base of the plates were implanted in the skin. The most currently accepted arrangement of the back plates of Stegosaurus is in two alternating rows, with the bones oriented vertically.

Why It’s a Top NHMU Dinosaur: Stegosaurus armatus was first named by Othniel Charles Marsh (famous combatant with Edward Cope in the “Dinosaur Wars” of the 19th century) in 1877. At least two other species of Stegosaurus have been found in the Upper Jurassic of Utah, Colorado, and Wyoming. One specimen of Stegosaurus has even been found in Portugal! Held vertically, the plates would have provided little protection; suggested uses include temperature regulation, attracting a mate, and signaling to other members of the same species. The four tail spikes were likely used at least in part for protection – this is supported by broken and healed spikes, and damage to bones of Allosaurus consistent with a tail spike strike!

Where Can I See It?: The Past Worlds Gallery of the Natural History Museum of Utah; Dinosaur National Monument (; North American Museum of Ancient Life at Thanksgiving Point (


Suggested Reading/References:

Galton, P. M. 2010. Species of plated dinosaur Stegosaurus (Morrison Formation, Late Jurassic) of western USA: new type species designation needed. Swiss Journal of Geosciences 103:187-198.

Galton, P. M., and P. Upchurch. 2004. Stegosauria; pp. 343-362 in D. B. Weishampel, P. Dodson, and H. Osmólska (eds.), The Dinosauria, 2nd Edition. University of California Press, Berkeley.

Maidment, S. C. R., D. B. Norman, P. M. Barrett, and P. Upchurch. 2008. Systematics and phylogeny of Stegosauria (Dinosauria: Ornithischia). Journal of Systematic Palaeontology 6:367-407.

Maidment, S. C. R. 2010. Stegosauria: a historical review of the body fossil record and phylogenetic relationships. Swiss Journal of Geosciences 103:199-210.

Ostrom, J. H., and J. S. McIntosh. 1999. Marsh's Dinosaurs: The Collections from Como Bluff. Yale University Press, New Haven.

Author: Joshua Lively

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