Name: ‭ ‬Pakicetus ‭(‬Pakistan whale‭)‬.
Phonetic: Pa-kee-see-tuss.
Named By: Gingerich‭ & ‬Russell‭ ‬-‭ ‬1981.
Classification: Chordata,‭ ‬Mammalia,‭ ‬Cetacea,‭ ‬Archaeoceti,‭ ‬Pakicetidae,‭ ‬Pakicetinae.
Species: P.‭ ‬inachus‭ (‬type‭)‬,‭ ‬P.‭ ‬attocki‭ ‬,‭ ‬P.‭ ‬calcis,‭ ‬P.‭ ‬chittas.
Diet: Carnivore.
Size: Between 1 and 2 meters long.
Known locations: Pakistan.
Time period: Ypresian to early Bartonian of the Eocene.
Fossil representation: Several individuals of partial remains.

       Pakicetus may well be the oldest known ancestor to modern whales,‭ ‬and along with other animals such as Ambulocetus,‭ ‬represent the group of terrestrial carnivores that began developing adaptations for a wholly aquatic lifestyle.
       Due to its transitional nature,‭ ‬it is hard to say with certainty how Pakicetus lived.‭ ‬Its ear structure is more developed for hearing in the air.‭ ‬Other forms such as the aforementioned Ambulocetus had ears that worked best when submerged in the water.‭ ‬This indicates that Pakicetus itself spent more time out of the water than in it.
       Analysis of the fossil site indicates that it was a coastal region at the time,‭ ‬and as such possibly had many estuaries and islands.‭ ‬Pakicetus has been envisioned by some as a wolf sized predator that would dive into the water after fish.‭ ‬In this scenario it could have focused its attention upon prey that had become trapped in tidal pools at low tide.‭
       The bones of Pakicetus indicate dense bone growth,‭ ‬a well-known adaptation in animals that spend a lot of time in the water.‭ ‬This bone analysis combined with the positioning of the eyes near the top of the skull has brought the second hunting theory of lurking in the water like a crocodile.
       Either way it may be that these marine adaptations are not just driven by predatory forces but practical ones too.‭ ‬Pakicetus may have had to cover a lot of ground to find food,‭ ‬and the rising and falling tides may have cut off some areas of the coast,‭ ‬creating islands at high tide that would have had‭ ‬passable land bridges at low tide.‭ ‬By evolving into a body that could provide efficient aquatic movement,‭ ‬Pakicetus would have had an advantage in not having to wait for the low tide.

More information on these whales can be found on their respective pages; 1 - Pakicetus,
2 - Ambulocetus, 3 - Rodhocetus, 4 - Dorudon, 5, Brygmophyseter, 6 - Diorocetus.

Further reading
- Middle Eocene large mammal assemblage with Tethyan affinities, Ganda Kas region, Pakistan. - Journal of Paleontology 54(3):508-533 - R. M. West - 1980.
- Pakicetus inachus, A New Archaeocete (Mammalia, Cetacea) from the Early-Middle Eocene Kuldana Formation of Kohat (Pakistan) - Contributions from the Museum of Paleontology, The Museum of Michigan 25 (11): 235–246 - Philip D. Gingerich & Donald E. Russell - 1981.
- Origin Of Underwater Hearing In Whales - Nature 361 (6411): 444–445. - J. G. M. Thewissen & S. T. Hussain - 1993.
- New middle Eocene archaeocetes (Cetacea: Mammalia) from the Kuldana Formation of northern Pakistan. - Journal of Vertebrate Paleontology 29(4):1289-1299 - L. N. Cooper, J. G. M. Thewissen & S. T. Hussain - 2009.
- From Land to Water: the Origin of Whales, Dolphins, and Porpoises - Evolution: Education and Outreach 2 (2): 272–288. - J. G. M. Thewissen, L. N. Cooper, J. C. George & S. Bajpai - 2009.


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