Zoologists refer to manatees and dugongs as "sea cows" but a simple internet search might return the more playful moniker "floaty potatoes." While only four species of the round, slow-moving aquatic herbivores of the order Sirenia remain on Earth -- and all are considered vulnerable to extinction -- fossil evidence suggests that many different kinds of sea cows lived in the past, and at times numerous species coexisted. Over their long history sea cows have lived along the coasts of every continent but Antarctica.