The evolutionary history of cetaceans is thought to have occurred in the Indian subcontinent from even-toed ungulates 50 million years ago, over a period of at least 15 million years. Cetaceans are fully aquatic marine mammals belonging to the order Artiodactyla, and branched off from other artiodactyls around 50 mya (million years ago). Cetaceans are thought to have evolved during the Eocene or earlier, sharing a closest common ancestor with hippopotamuses. Being mammals, they surface to breathe air; they have finger bones in their fins; they nurse their young; and, despite their fully aquatic life style, they retained many skeletal features from their terrestrial, mammalian ancestors. These mammalian characteristics all point to their terrestrial origin, also the first mammals were terre