Stegosaurus STEG-uh-SOR-us
"Roofed lizard"
You 1.8 m (5.9 ft) tall
Stegosaurus 9 m (29.5 ft) long
6 people holding hands
- Length
- 9 m (29.5 ft) — About 9 m long, 4 m tall at the shoulder, ~3.5 tonnes.
- Period
- Late Jurassic (155–145 Mya)
- Place
- North America · Western United States · Portugal
- Food
- Herbivore — Low-growing ferns, cycads, and horsetails. Probably stripped soft plants with a beak.
Stegosaurus is the dinosaur that looks like nothing else alive today — a plant-eater the size of a bus, with a double row of upright bony plates along its back and four spikes on its tail. It walked on four legs but the back legs were much longer than the front, so its body sloped forward from the hips.
Stegosaurus lived in the Late Jurassic, about 150 million years ago. That puts it closer in time to Tyrannosaurus rex than T. rex is to us — children’s books that show them fighting are mixing two periods 85 million years apart.
What we know
- Two staggered rows of large bony plates ran along the back.
- Four long spikes on the tail — paleontologists call this the 'thagomizer'.
- Skull was tiny relative to body — the brain was about the size of a walnut.
- Lived alongside Allosaurus, Apatosaurus, and Diplodocus in the Morrison Formation.
What we guess
- What the plates were for. Old idea: armor. Newer ideas: heat regulation, species display, or threat advertising. Probably all three at once.
- Whether the plates were brightly colored in life — possible but unprovable.
- How exactly the tail spikes were used. Allosaurus vertebrae with stegosaur-spike-shaped wounds suggest defense, not just display.