Temporal range: Early Eocene
|Cast of P. attocki, ROM|
Gingerich & Russell, 1981
Pakicetus is a genus of extinct terrestrial carnivorous whale of the family Pakicetidae which was endemic to Pakistan from the Eocene (55.8-40.4) Ma). The vast majority of paleontologists regard it as a basal whale closely related to the direct ancestors of modern day whales.
Pakicetus was assigned to Protocetidae by Gingerich and Russell (1981), Carroll (1988) and Benton (1993). Then to Pakicetinae by Gingerich and Russell (1990) and McKenna and Bell (1997); and to Pakicetidae by Thewissen and Hussain (1998), Thewissen et al. (2001), Thewissen et al. (2001), Geisler and Sanders (2003), McLeod and Barnes (2008) and Uhen (2010).
Fossil distribution 
The first fossils were uncovered in Pakistan, hence their name. The strata of western Pakistan where the fossils were found was then the coastal region of the Tethys Sea. The first fossil found of the creature consisted of an incomplete skull with a skull cap and a broken mandible with some teeth. It was thought to be from a mesonychid, but Gingerich and Russell recognized it as an early cetacean from characteristic features of the inner ear, found only in cetaceans: the large auditory bulla is formed from the ectotympanic bone only. This suggests that it is a transitional species between extinct land mammals and modern cetaceans. It was illustrated on the cover of Science as a semiaquatic, somewhat crocodilelike mammal, diving after fish.
Possible semi-aquatic nature 
Somewhat more complete skeletal remains were discovered in 2001, prompting the view that Pakicetus was primarily a land animal about the size of a wolf, and very similar in form to the related mesonychids. In 2001, J. G. M. Thewissen and colleagues wrote that "Pakicetids were terrestrial mammals, no more amphibious than a tapir."
However, in 2009 Thewissen et al. 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. Just like Indohyus, limb bones of pakicetids are osteosclerotic, also suggestive of aquatic habitat" (since heavy bones provide ballast).
In popular culture 
The creature was featured in an episode of Paleoworld called Back to the Seas, where it was portrayed as a semi-aquatic crocodilelike mammal, as it was believed to be at the time. It was also portrayed as a descendant of the mesonychids and an ancestor of Ambulocetus.
See also 
- Paleobiology Database: Pakicetus basic info
- P. D. Gingerich & D. E. Russell, Pakicetus inachus, a new archaeocete (Mammalia, Cetacea) from the early-middle Eocene Kuldana Formation of Kohat (Pakistan). Univ. Mich. 1981, Contr. Mus. Paleont, Vol 25, 235–246
- Science 22 April 1983: Online Table of Contents.
- Thewissen, J. G. M.; Williams, E. M.; Roe, L. J.; Hussain, S. T. (2001). "Skeletons of terrestrial cetaceans and the relationship of whales to artiodactyls". Nature 413 (6853): 277–281. doi:10.1038/35095005. PMID 11565023.
- Thewissen, J. G. M.; Cooper, Lisa Noelle; George, John C.; Bajpai, Sunil (2009). "From Land to Water: the Origin of Whales, Dolphins, and Porpoises". Evolution: Education and Outreach 2 (2): 272–288. doi:10.1007/s12052-009-0135-2.