Sirenians first appeared in the fossil record in the Early Eocene and significantly diversified throughout the epoch. They inhabited rivers, estuaries, and nearshore marine waters. Sirenians, unlike other marine mammals such as cetaceans, lived in the New World. One of the earliest aquatic sirenians discovered is "Prorastomus" which dates back to 40 million years ago, and the first known sirenian, the quadruped "Pezosiren", lived 50 million years ago. An ancient sirenian fossil of a petrosal bone was found in Tunisia, dating back to approximately the same time as "Prorastomus". This is the oldest sirenian fossil to be found in Africa and supports molecular data suggesting that sirenians may have originated in Africa. Prorastomidae and Protosirenidae, the earliest sirenian families, consisted of pig-like amphibious creatures who died out at the end of the Eocene. When the Dugongidae appeared at this time, sirenians had evolved the characteristics of modern variety, including an aquatic streamlined body with flipper-like front legs with no hind limbs, and a powerful tail with horizontal caudal fins which uses an up-and-down motion to move them through the water.