The extinct cetacean commonly identified as the earliest known ancestor of whales is Pakicetus. Living about 50 million years ago in the early Eocene, this wolf-sized animal still had four functional legs and looked more like a land mammal than a modern whale.
Its fossils were first found in Pakistan, giving the genus its name: “Pakicetus” means “whale from Pakistan.” Scientists classify it as an early cetacean largely because of distinctive features in its ear bones, which connect it to the whale lineage. Its teeth and skull also show a mixture of terrestrial mammal and early whale traits.
Pakicetus probably lived near freshwater and may have eaten fish as well as other small animals. Later forms such as Ambulocetus became more clearly adapted to swimming, while protocetids and basilosaurids moved farther toward fully aquatic life.
Strictly speaking, Pakicetus is not proven to be the direct parent of every later whale; fossils usually represent close branches rather than documented parent-and-child sequences. In quiz usage, however, it is the canonical answer for the earliest known whale ancestor.