Topic summary
Toothed whales
Extracted from the Wikipedia article Toothed whale.
Evolution
Toothed whales, along with baleen whales, are descendants of land-dwelling mammals of the artiodactyl order (even-toed ungulates). They are closely related to the hippopotamus, sharing a common ancestor that lived around 54 million years ago (mya). The primitive cetaceans, or archaeocetes, first took to the sea approximately 49 mya and became fully aquatic within 5–10 million years. The ancestors of toothed whales and baleen whales diverged in the early Oligocene. This was due to a change in the climate of the southern oceans that affected the environment of the plankton that these whales ate.