Stegosaurus

'Stegosaurus was a saber-toothed sauropod that lived in North America during the Late Jurassic Period (approximately 155 to 150 million years ago). It was characterized by 17 bony plates (up to 60 cm) arranged in two rows along its back and four spines (tagomizers) on the tip of its tail. The function of the plates has long been debated, but it is now believed that their primary function was to regulate body temperature. This is because the vasculature inside the periosteum is well suited to thermoregulation and was too weak for defense. Stegosaurus had a very small brain, about the size of a walnut (about 80 grams), making it one of the smallest dinosaurs in terms of brain size relative to body weight. The spines on the tail were effective in defending against predators, and allosaur fossils have shown signs of injury from stegosaur tail spines.