The stegosaurus was a large, plant-eating dinosaur that lived during the late Jurassic period, around 155 to 150 million years ago. It is easily recognized by its distinctive double row of large, bony plates along its back and the spikes on its tail, known as the thagomizer. Stegosaurus could grow up to 30 feet long and weighed around 5 tons. Despite its size, the stegosaurus had a small brain compared to its body, which led to the belief that it was not very intelligent. It primarily fed on low-lying plants and used its strong legs to move through its habitat, which included forests and open plains.