Scientists believe that a predatory dinosaur called Spinosaurus aegypticus may have been 52 to 59 feet (16 to 18 meters) long, making it one of the largest predators, if not the largest. The animal’s long spine evolved during the Early Cretaceous period. (In fact, one vertebra of a Spinosaurus is taller than the average human.) The tall spines formed a skin-encased, sail-like structure; some scientists suggest that the long spine was needed to hold the sails. No one knows the function of the structure, but there are some theories. One states that, because the animals lived in the tropics close to sea level, the sails may have been used to cool off the animals. Another idea is that the sails were used for attracting potential mates, or for scaring off potential rivals or other dinosaur predators.