English: Size of the pakicetid Pakicetus, compared to a human. Brown silhouette shows Pakicetus as a terrestrial, dog-like animal is based on skeletal drawing (which in turn is a composite of different specimens published by Thewissen et.al. (2001)).^[1] Green silhouette outlines an alternative restoration by John Klausmeyer (University of Michigan Exhibit Museum) of Pakicetus as an aquatic, swimming animal (measuring about 1.4 meters long).^[2][3]

When Pakicetus became known to science in the early 1980s, the only known remains consisted of fragments of a skull (GSP-UM 084) and a jaw fragment with some teeth (GSP-UM 081). ^[4] From these remains, Pakicetus was reconstructed and suggested to represent an “amphibious stage” in whale evolution that “may still spent a significant amount of time on land”. ^[5] In 2001, Thewissen et.al. published additional bones referred to Pakicetus and concluded that it was a terrestrial animal.^[1]

Philip Gingerich have repeatedly claimed the reconstruction of Pakicetus as a terrestrial animal to be “controversial”.^[2]He points out that the conclusion by Thewissen et.al. that Pakicetus was terrestrial is “based on isolated bones found in a quarry where pakicetid and land mammal bones are mixed together–circumstances unlikely to convince many skeptics”^[6] and argue it was made “with little explanation”.^[2] Gingerich have defended his original depiction of Pakicetus as a semiaquatic animal, based the aquatic adaptations he originally described, ^[6] and subsequently^[2] on the basis of its hearing mechanism,^[7] the ilium, ^[8] bone microstructure^[9] and long toe bones (indicating webbed feet for swimming).^[2] Gingerich have repeatedly favoured the depiction by John Klausmeyer. ^[2][6][3]

Sources

1. ↑ ^{a b} Thewissen J.G.M., Williams E.M., Roe L.J. & Hussain S.T. (2001). "Skeletons of terrestrial cetaeans and the relationship of whales to artiodactyls", Nature 413(6853): p. 277-281. DOI: 10.1038/35095005
2. ↑ ^{a b c d e f} Gingerich P.D. 2012, “Evolution of Whales from Land to Sea”, Proceedings of the American Philosophical Society 156(3): p. 309-323
3. ↑ ^{a b} Gingerich P.D. (2015). “Evolution of Whales from Land to Sea”, in Dial K.P., Shubin N & Brainerd E.L. (eds.). Great Transformations in Vertebrate Evolution (University of Chicago Press), p. 239-256
4. ↑ [1]
5. ↑ [2]
6. ↑ ^{a b c} [3]
7. ↑ [4]
8. ↑ [5]
9. ↑ [176:TPSOEE2.0.CO;2.short]