Hippos are mammals. A mammal has hair or fur, most are born alive, and the young are fed milk from their mom. Hippos start as an egg inside their mom's stomach. The egg gets fertilized and they turn into an embryo. When they are born, they become calfs or babies. Once they grow up and reach adulthood the male hippo get the title bull. If you're a female hippo you gain the title cow. Eventually hippo's die.