More than 80 living species of mammals are classified as whales, or cetaceans from ketos, the Greek name for sea monster. To early mariners these magnificent gigantic creatures were considered no less than monsters from the deep, and many stories attributed to adventures and encounters with whales ascribe to their impact on humanity. We can trace the origin of whales to the Eocene epoch lasting from approximately 55 million to 34 million years ago. It was during this period the gradual evolution of whales transformed them from land dwelling to sea dwelling mammals.
From recent fossil discoveries, it is believed that early relatives of whales walked on land as furred and hoofed carnivores. Evolving into a heavy-headed and short species having elongated jaws similar to crocodiles and alligators, they began to hunt amphibious animals from shallow water. The closest living relatives to whales are the hippopotamus species that spends most of the time semi-submerged in shallow waters.
Palaeontologists considered the early forms of cetaceans were four-legged land animals that took to the water in order to feed on fish. These early animals hunted in rivers and lakes, evidence found in fossilised remains determined from the mixture of oxygen in the bones that they swam only in fresh water. It was over the period of approximately 10 million years of so that these creatures gradually began to move out into seawater. These land dwelling animals were discovered to have a highly unusual shaped ear region that resembles those of modern whales studied today.
From their early beginnings on land, whales evolved into the giant air-breathing sea creatures we are familiar with today. As an occasional reminder of their land-dwelling ancestors, whales are sometimes born with one or two legs however they are now exclusively sea dwelling creatures that add to the diversity and beauty of our worlds' oceans and seas.