Stegosaurus could be up to 9 m long and 4 m tall - as big as a bus. On its back it sported large bone plates which could measure up to 6 cm high and 6 cm wide. For a long time it was considered the stupidest dinosaur, because its brain was no larger than a tennis ball and weighed only 8 g, especially considering that its body weighed 4.5 tonnes. Today we believe that it had a kind of second brain in the base of its tail. Its teeth were too pointed for chewing, so the herbivore swallowed stones, which crushed the food in its stomach.