Article | Published:

Skeletons of terrestrial cetaceans and the relationship of whales to artiodactyls

Naturevolume 413pages277281 (2001) | Download Citation



Modern members of the mammalian order Cetacea (whales, dolphins and porpoises) are obligate aquatic swimmers that are highly distinctive in morphology, lacking hair and hind limbs, and having flippers, flukes, and a streamlined body. Eocene fossils document much of cetaceans' land-to-water transition, but, until now, the most primitive representative for which a skeleton was known was clearly amphibious and lived in coastal environments. Here we report on the skeletons of two early Eocene pakicetid cetaceans, the fox-sized Ichthyolestes pinfoldi, and the wolf-sized Pakicetus attocki. Their skeletons also elucidate the relationships of cetaceans to other mammals. Morphological cladistic analyses have shown cetaceans to be most closely related to one or more mesonychians, a group of extinct, archaic ungulates, but molecular analyses have indicated that they are the sister group to hippopotamids. Our cladistic analysis indicates that cetaceans are more closely related to artiodactyls than to any mesonychian. Cetaceans are not the sister group to (any) mesonychians, nor to hippopotamids. Our analysis stops short of identifying any particular artiodactyl family as the cetacean sister group and supports monophyly of artiodactyls.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.


All prices are NET prices.


  1. 1

    Hulbert, R. C. Jr, Petkewich, R. M., Bishop, G. A., Bukry, D. & Aleshire, D. P. A new middle Eocene protocetid whale (Mammalia: Cetacea: Archaeoceti) and associated biota from Georgia. J. Paleontol. 72, 907–927 (1998).

  2. 2

    Thewissen, J. G. M. & Hussain, S. T. Systematic review of the Pakicetidae, early and middle Eocene Cetacea (Mammalia) from Pakistan and India. Bull. Carnegie Mus. Nat. Hist. 34, 220–238 (1998).

  3. 3

    Luo, Z. & Gingerich, P. D. Terrestrial Mesonychia to aquatic Cetacea: transformation of the basicranium and evolution of hearing in whales. Univ. Michigan Pap. Paleontol. 31, 1–98 (1999).

  4. 4

    O'Leary, M. A. & Geisler, J. H. The position of Cetacea within Mammalia: phylogenetic analysis of morphological data from extinct and extant taxa. Syst. Biol. 48, 455–490 (1999).

  5. 5

    Uhen, M. D. New species of protocetid archaeocete whale, Eocetus wardii (Mammalia, Cetacea) from the middle Eocene of North Carolina. J. Paleont. 73, 512–528 (1999).

  6. 6

    Luo, Z. in The Emergence of Whales: Evolutionary Patterns in the Origin of Cetacea (ed. Thewissen, J. G. M.) 269–301 (Plenum, New York, 1998).

  7. 7

    Thewissen, J. G. M., Hussain, S. T. & Arif, M. Fossil evidence for the origin of aquatic locomotion in archaeocete whales. Science 263, 210–212 (1994).

  8. 8

    Thewissen, J. G. M., Madar, S. I. & Hussain, S. T. Ambulocetus natans, an Eocene cetacean (Mammalia) from Pakistan. Courier Forschungsinstitut Senckenberg 191, 1–86 (1996).

  9. 9

    Thewissen, J. G. M. & Fish, F. E. Locomotor evolution in the earliest cetaceans: functional model, modern analogues, and paleontological evidence. Paleobiology 23, 482–490 (1997).

  10. 10

    Milinkovitch, M. C. & Thewissen, J. G. M. Even-toed fingerprints on whale ancestry. Nature 388, 622–624 (1997).

  11. 11

    Luo, Z. In search of whales' sisters. Nature 404, 235–237 (2000).

  12. 12

    Gingerich, P. D., Russell, D. E. & Shah, S. M. I. Origin of whales in epicontinental remnant seas: new evidence from the early Eocene of Pakistan. Science 220, 403–406 (1983).

  13. 13

    Kellogg, R. A Review of the Archaeoceti (Carnegie Inst. Washington, Washington, 1936).

  14. 14

    Gingerich, P. D., Smith, B. H. & Simons, E. L. Hind limbs of Eocene Basilosaurus: evidence of feet in whales. Science 249, 154–157 (1990).

  15. 15

    Uhen, M. D. in The Emergence of Whales: Evolutionary Patterns in the Origin of Cetacea (ed. Thewissen, J. G. M.) 29–61 (Plenum, New York, 1998).

  16. 16

    Bajpai, S. & Thewissen, J. G. M. A new diminutive Eocene whale from Kachchh (Gujarat, India) and its implications for locomotor evolution of cetaceans. Curr. Sci. 79, 1478–1482 (2000).

  17. 17

    Zhou, X., Sanders, W. J. & Gingerich, P. D. Functional and behavioral implications of vertebral structure in Pachyaena ossifraga (Mammalia, Mesonychia). Contrib. Mus. Paleontol. Univ. Michigan 28, 289–319 (1992).

  18. 18

    Thewissen, J. G. M. & Hussain, S. T. Postcranial osteology of the most primitive artiodactyl Diacodexis pakistanensis (Dichobunidae). Anat. Histol. Embryol. 19, 37–48 (1990).

  19. 19

    Madar, S. I., Thewissen, J. G. M. & Hussain, S. T. Additional holotype remains of Ambulocetus natans (Cetacea, Ambulocetidae), and their implications for locomotion in early whales. J. Vertebr. Paleont. (in the press).

  20. 20

    Howell, A. B. Aquatic Mammals: Their Adaptations to Life in the Water (Charles Thomas, Baltimore, 1930).

  21. 21

    Howell, A. B. Speed in Animals: Their Specializations for Running and Leaping (Univ. Chicago Press, Chicago, 1944).

  22. 22

    King, J. E. Seals of the World (Cornell Univ. Press, Ithaca, 1991).

  23. 23

    Shaeffer, B. Notes on the origin and function of the artiodactyl tarsus. Am. Mus. Novit. 1356, 1–26 (1947).

  24. 24

    Thewissen, J. G. M. & Madar, S. I. Ankle morphology of the earliest cetaceans and its implications for the phylogenetic relations among ungulates. Syst. Biol. 48, 21–30 (1999).

  25. 25

    Vaughan, T. A. Mammalogy (Saunders College, New York, 1986).

  26. 26

    Bajpai, S. & Thewissen, J. G. M. in The Emergence of Whales: Evolutionary Patterns in the Origin of Cetacea (ed. Thewissen, J. G. M.) 213–233 (Plenum, New York, 1998).

  27. 27

    Weber, M. Die Säugetiere (Gustav Fischer, Jena, 1928).

  28. 28

    Gingerich, P. D., Raza, M. S., Arif, M., Anwar, M. & Zhou, X. New whale from the Eocene of Pakistan and the origin of cetacean swimming. Nature 368, 844–847 (1994).

  29. 29

    O'Leary, M. A. & Uhen, M. D. The time of origin of whales and the role of behavioral changes in the terrestrial-aquatic transition. Paleobiology 25, 534–556 (1999).

  30. 30

    Thewissen, J. G. M., Williams, E. M. & Hussain, S. M. Eocene mammal faunas from northern Indo-Pakistan. J. Vertebr. Paleont. 21, 347–366 (2001).

  31. 31

    Thewissen, J. G. M. & Hussain, S. T. Origin of underwater hearing in whales. Nature 361, 444–445 (1993).

  32. 32

    Hemilä, S., Nummela, S. & Reuter, T. A model of the odontocete middle ear. Hearing Res. 133, 82–97 (1999).

  33. 33

    Rado, R., Himelfarb, M., Arensberg, B., Terkel, J. & Wollberg, Z. Are seismic communication signals transmitted by bone conduction in the blind mole rat? Hearing Res. 41, 23–30 (1989).

  34. 34

    Lenhardt, M. L. Bone conduction hearing in turtles. J. Audit. Res. 22, 153–160 (1982).

  35. 35

    Geisler, J. H. & Luo, Z. in The Emergence of Whales: Evolutionary Patterns in the Origin of Cetacea (ed. Thewissen, J. G. M.) 163–212 (Plenum, New York, 1998).

  36. 36

    O'Leary, M. A. in The Emergence of Whales: Evolutionary Patterns in the Origin of Cetacea (ed. Thewissen, J. G. M.) 133–161 (Plenum, New York, 1998).

  37. 37

    Luckett, W. P. & Hong, N. Phylogenetic relationships between the orders Artiodactyla and Cetacea: a combined assessment of morphological and molecular evidence. J. Mamm. Evol. 5, 127–182 (1998).

  38. 38

    Shimamura, M. et al. Molecular evidence from retroposons that whales form a clade within even-toed ungulates. Nature 388, 666–670 (1997).

  39. 39

    Gatesy, J. in The Emergence of Whales: Evolutionary Patterns in the Origin of Cetacea (ed. Thewissen, J. G. M.) 63–111 (Plenum, New York, 1998).

  40. 40

    Milinkovitch, M. C., Bérubé, M. & Palsbøll, P. J. in The Emergence of Whales: Evolutionary Patterns in the Origin of Cetacea (ed. Thewissen, J. G. M.) 113–131 (Plenum, New York, 1998).

  41. 41

    Nikaido, M., Rooney, A. P. & Okada, N. Phylogenetic relationships among cetartiodactyls based on insertions of short and long interspersed elements: hippopotamuses are the closest extant relatives of whales. Proc. Natl Acad. Sci. USA 96, 10261–10266 (1999).

  42. 42

    Gentry, A. W. & Hooker, J. J. in The Phylogeny and Classification of the Tetrapods, Vol. 2: Mammals (ed. Benton, M. J.) 235–272 (Clarendon, Oxford, 1988).

  43. 43

    Bajpai, S. & Gingerich, P. D. A new Eocene archaeocete (Mammalia, Cetacea) from India and the time of origin of whales. Proc. Natl Acad. Sci. USA 95, 15464–15468 (1998).

  44. 44

    Thewissen, J. G. M. Phylogenetic aspects of cetacean origins: a morphological perspective. J. Mammal. Evol. 2, 157–184 (1994).

  45. 45

    Thewissen, J. G. M., Madar, S. I. & Hussain, S. T. Whale ankles and evolutionary relationships. Nature 395, 452 (1998).

  46. 46

    Naylor, G. J. P. & Adams, D. C. Are the fossil data really at odds with the molecular data? Morphological evidence for Cetartiodactyla phylogeny reexamined. Syst. Biol. 50, 444–453 (2001).

  47. 47

    Swofford, D. L. PAUP 4.0b8 Phylogenetic Analysis Using Parsimony (and Other Methods) (Sinauer, Sunderland, Massachusetts, 1998).

  48. 48

    Gingerich, P. D., Haq, M.-u., Zalmout, I., Khan, I. H. & Malkani, M. S. Origin of whales from early artiodactyls: hands and feet of Eocene Protocetidae from Pakistan. Science (in the press).

Download references


We thank M. Arif, S. Bajpai, J. Erfurt, A. Friscia, M. Hellmund, S. Madar, M. Raza, J. Quade and the Geological Survey of Pakistan for assistance in field work, access to collections and laboratories, and/or discussions. M. Tomasko prepared Fig. 1. Funding for this research was provided by the National Science Foundation (EAR 9902830).

Author information


  1. Department of Anatomy, Northeastern Ohio Universities College of Medicine, Rootstown, 44272, Ohio, USA

    • J. G. M. Thewissen
    •  & E. M. Williams
  2. Department of Geosciences, University of Arizona, Tucson, 85721, Arizona, USA

    • L. J. Roe
  3. Department of Anatomy, Howard University, College of Medicine, Washington, 20059, DC, USA

    • S. T. Hussain


  1. Search for J. G. M. Thewissen in:

  2. Search for E. M. Williams in:

  3. Search for L. J. Roe in:

  4. Search for S. T. Hussain in:

Corresponding author

Correspondence to J. G. M. Thewissen.

Supplementary information

About this article

Publication history



Issue Date


Further reading


By submitting a comment you agree to abide by our Terms and Community Guidelines. If you find something abusive or that does not comply with our terms or guidelines please flag it as inappropriate.