Why do hippos have big jaws?

Hippopotamus (hippopotamus amphibius) or hippo have 40 teeth. They have a pair of huge incisors (up to 18 inches long), curved lower canine teeth (ivory, grow up to 3 feet), and flat molars used for grinding up vegetation. Their teeth are used to defend their spot in the water hole in which they spend most of their day, in which they are very territorial.