Ask aDino Field Guide ← Jurassic

Artist's reconstruction · realistic art coming in a later version

Stegosaurus

STEG-uh-SOR-us

“Roof Lizard”

Jurassic
When
Late Jurassic
Where
North America
Size
30 ft long
Diet
Plants only

25 Facts

1–25
  1. Stegosaurus lived about 150 million years ago in the Late Jurassic period.
  2. Its name means “Roof Lizard” because scientists first thought the plates lay flat on its back like roof tiles.
  3. It was about 30 feet long — roughly the length of a school bus.
  4. It weighed up to 5 tons, about the same as an African elephant.
  5. It had 17 large bony plates running down its back and tail in two staggered rows.
  6. The biggest plates were over 2 feet tall — bigger than a kindergartener.
  7. Scientists still argue about what the plates were actually for. The top guesses: temperature control, showing off to other Stegosaurus, or scaring predators.
  8. The plates had blood vessels running through them, which is why temperature control is such a popular theory.
  9. The plates may have been able to flush with color by filling with blood — like a giant mood ring.
  10. Its tail had four sharp spikes that scientists call a “thagomizer.”
  11. The word “thagomizer” came from a cartoon! Far Side cartoonist Gary Larson invented it in 1982, and paleontologists liked it so much they made it official.
  12. The tail spikes were up to 3 feet long and very sharp.
  13. Fossils show Stegosaurus actually used its tail to fight — Allosaurus bones have been found with thagomizer-shaped puncture wounds.
  14. Stegosaurus was a plant-eater (herbivore) and ate ferns, mosses, and low bushes.
  15. It had a tiny brain — about the size of a hot dog — even though its body was huge.
  16. For a long time scientists thought it had a “second brain” in its hips. That wasn’t a brain, but it did have an unusually large nerve cluster there.
  17. It walked on four legs, with longer back legs than front legs, giving it a sloped-down shape.
  18. Its head was held very low to the ground, perfect for munching low plants.
  19. It had a beak at the front of its mouth for clipping plants, and small flat teeth in the back.
  20. Stegosaurus is the state fossil of Colorado, where many of its bones have been found.
  21. The first Stegosaurus fossil was discovered in 1877 by Arthur Lakes near Morrison, Colorado.
  22. Its closest relatives were other plated dinosaurs like Kentrosaurus and Hesperosaurus.
  23. It lived alongside Allosaurus (its main predator), Brachiosaurus, Diplodocus, and Apatosaurus.
  24. Despite being one of the most famous dinosaurs, only about 80 specimens have ever been found.
  25. Stegosaurus went extinct around 145 million years ago, long before T. rex appeared. They never met!