Pakicetids

Pakicetids (formally known as Pakicetidae) are a family of extinct animals that are the earliest known cetaceans. While modern-day cetaceans are all water-dwelling animals such as whales and dolphins, the pakicetids pre-date the transition from land.

There are three known genera of pakicetids, the wolf-sized Pakicetus, Nalacetus, and the fox-sized Ichthyolestes. Pakicetus was the first discovered (in 1983, by Philip Gingerich, Neil Wells, Donald Russell, and S. M. Ibrahim Shah) and all three species are known from a few sites in Pakistan, hence the name of the first genera and the family as a whole. The region is believed to have been coastal to the Tethys Sea when the pakicetids lived, some 52 million years ago.

The pakicetids were carnivorous land animals, but are presumed to be ancestors of modern whales because of peculiarities in the bones of the ear, peculiarities which have only been found in whales. The current theory is that modern whales evolved from archaic whales such as Basilosaurids, which in turn evolved from something like the amphibious Ambulocetids, which themselves evolved from something like the land-dwelling Pakicetids.