You better beware this dino’s tail.

A hungry Allosaurus runs up to Stegosaurus, ready to attack. But as it gets close, Stegosaurus swings its heavy tail, and—whack! One of its thick, pointy spikes drives into Allosaurus’ tailbone. Allosaurus limps away, and Stegosaurus continues to munch ferns and young trees.

Puzzling plates

Stegosaurus is famous for its two rows of kite-shaped plates that stick out from its neck, back, and tail. But the paleontologist who first discovered a Stegosaurus fossil thought the plates laid flat on its back like a turtle’s shell. That’s why its name in Greek means “roof lizard.”

So why does Stegosaurus have these plates? Some scientists think they were used to attract mates, similar to the frill on a TriceratopsOthers think the plates protected Stegosaurus from attacking predators or absorbed heat from the sun to help warm the animal. Although the plates are still a mystery, fossilized footprints reveal that this dino likely traveled in family groups.

Experts think that Stegosaurus’s tail was its main method of defense. The dino could swing its large tail from side to side with great force. A fossilized tailbone of Allosaurus has a hole in it the size of a Stegosaurus tail spike—ouch!

Butt brain?

Stegosaurus lived about 145 million years ago during the Jurassic period in what’s now Colorado, Utah, and Wyoming. It was about the length of a bus and weighed almost 14,000 pounds. But this enormous animal had a brain that was only slightly larger than a walnut. 

One early paleontologist believed that Stegosaurus had a second brain in its tail because the expert noticed a cavity like those where the brain would be in its rump. But that’s a busted myth—the empty space likely held a mass of tissue that might have helped produce extra energy or was simply a fluid-filled gland. 


Ali and Sean travel back 150 million years to the Jurassic period to get a look at a flying dinosaur called the Anchiornis. Tour guide Simon reveals that this dinosaur actually had feathers!