Pakicetus (meaning 'whale from Pakistan') is an extinct genus of amphibious cetacean of the family Pakicetidae, which was endemic to Indian Subcontinent during the Ypresian (early Eocene) period, about 50 million years ago.

[5] Reconstructions of pakicetids that followed the discovery of composite skeletons often depicted them with fur; however, given their relatively close relationships with hippos, they may have had sparse body hair.

"[7] However, Thewissen et al. 2009 argued that "the orbits ... of these cetaceans were located close together on top of the skull, as is common in aquatic animals that live in water but look at emerged objects.

"[9] The Pakicetus skeleton reveals several details regarding the creature's unique senses and provides a newfound ancestral link between terrestrial and aquatic animals.

[4] Cetaceans also all categorically exhibit a large mandibular foramen within the lower jaw, which holds a fat pack and extends towards the ear, both of which are also associated with underwater hearing.

The fossils were found in the Kuldana Formation west of Islamabad in northern Pakistan and were dated as early to early-middle Eocene in age.

In contrast, the origin of cetaceans, which includes whales, began as four-legged land animals who actively used locomotion and were great runners as a result.

[14] The fossils came out of red terrigenous sediments bounded largely by shallow marine deposits typical of coastal environments caused by the Tethys Ocean.

During the Eocene, modern day Pakistan was part of an independent island-continent off the coastal region of Eurasia, and therefore an ideal habitat for the evolution and diversification of the Pakicetidae.