The stegosauruses, which had a short neck, small head and low brain-to-body mass ratio, which is a rough estimate of the intelligence of an animal, used their spiked tails as a defense against predators.
It had a short neck and a small head, meaning it most likely ate low-lying bushes and shrubs. Stegosaurus had a relatively low brain-to-body mass ratio. Today, it is generally agreed that their spiked tails were most likely used for defense against predators, while their plates may have been used primarily for display, and secondarily for thermoregulatory functions. Brain-to-body mass ratio, also known as the brain-to-body weight ratio, is the ratio of brain mass to body mass, which is hypothesized to be a rough estimate of the intelligence of an animal, although fairly inaccurate in many cases. 
