Manatees and dugongs live in warm, shallow, coastal waters, estuaries (where rivers meet the sea), and in slow moving rivers in tropical parts of the world. Manatees and dugongs have existed for more than 60 million years which means that they were around at the same time as the dinosaurs! Manatees and dugongs are members of the biological family named Sirenians: the dugong, the West Indian manatee, the West African manatee, and the Amazonian manatee. There once was a fifth type of Sirenian called the Stellar's sea cow, but it was over-hunted and became extinct about 230 years ago. When an animal becomes extinct it means that there are no longer any more of those animals anywhere in the world. The sea cow is gone forever, and swims only in our memories.