Temporal range: Eocene–Oligocene
|Cynthiacetus and Ambulocetus skeletons|
|Families and Clades|
Archaeocetes, or "ancient whales", are a paraphyletic group of primitive cetaceans that lived in the Eocene period ( ). Representing the earliest cetacean radiation, they include the initial amphibious stages in cetacean evolution and are thus the ancestors of the both modern cetacean suborders, Mysticeti and Odontoceti. This initial diversification occurred in the shallow waters that separated India and Asia , resulting in some 30 species adapted to a fully oceanic life; though both echolocation and filter-feeding evolved during a second radiation .
First identified as cetaceans by West 1980, the Pakicetids, the most archaic of whales, had long slender legs, a long narrow tail, and could reach the size of a modern wolf. They have only been found in sediments from freshwater streams in north-western India and northern Pakistan and were probably waders rather swimmers.
Dozens of fossils are known, but only of skulls, teeth, and jaw fragments; no complete skeletons have been found. The dentition varied: the smallest species had teeth like modern fish eaters, and the largest were more like modern hyenas. The pakicetids may have been predators or carrion feeders. Neither the skull nor the dentition of pakicetids resemble those of modern whales, but the sigmoid process, involucrum, pachyostotic (compact) and rotated ossicles of their ears still reveal their cetacean nature.
The next diverging family of whales, the Ambulocetids, were large, amphibious, and crocodile-like with large feet and a strong tail. Sediments indicate they lived in coastal areas and their compact bones suggest they were ambush rather than fast pursuit predators. Also known exclusively from Pakistan and India, the ambulocetids include the oldest known whale Himalayacetus, which is believed to be , some 4 million years older than the rest of its family.
Of the less than ten fossils that have been described, one, Ambulocetus natans, is nearly complete and the main source of information concerning early cetacean evolution. The size of a male sea lion, it had a large head with a long snout and robust, strongly worn teeth. The lower jaw shows that Ambulocetus had an unusual soft tissue connecting the back of the jaw to the middle ear — a small equivalent to the large sound-receiving fat pad in modern odontocetes. Its eyes were placed dorsally on the head, but were facing laterally. The musculature of the head, neck, and back was strong and the flute-less tail was long. The hindlimbs were short, but equipped with long feet. The forelimbs were also short and equipped with five short hoofs. Ambulocetus probably swam with its hindfeet like a modern otter, but moved slowly on land. It probably was an ambush hunter like modern crocodiles.
The Remingtonocetids had short limbs, and a strong and powerful tail with flattened vertebrae. Their long snout, tiny eyes, and ear morphology suggest their vision was poor and that hearing was their dominant sense. They too have only been found in Pakistan and India, and sediments suggest they lived in turbid waters in coastal areas. Though they were probably able to live on land, they apparently used their tails to swim.
Dozens of fossils have been described, but most are only skulls and lower jaws with few dental and postcranial remains. Remingtonocetids probably varied in size with the smallest species matching Pakicetus and the largest Ambulocetus. Remingtonocetids had longer snouts than other archaeocetes, but except that the cranial morphology also varied considerably, probably reflecting different diets. The eyes were small, but the ears were large and set far apart — probably reflecting an increased emphasis on underwater hearing. The fragmentary remains of Remintonocetid postcrania suggest that they had a long neck and large hindlimbs that were probably able to support the body weight on land.
The Protocetids, known from both Africa and America, were a diversified family with hind limbs and a strong tail, indicating that they were strong swimmers that colonized shallow and warm oceans, such as reefs. They greatly affected cetacean evolution , because they spread across Earth's oceans. They had long snouts, large eyes, and a nasal opening located farther up the head than in earlier archaecetes — suggesting they could breath with the head held horizontally, similar to modern cetaceans — a first step towards a blowhole. Their dentition varied, but started to evolve towards the non-masticating teeth of modern cetaceans, and they were probably active hunters. Their hindlimbs were reduced and probably short. In some species, the pelvis was not connected to the vertebral column, suggesting the hindlimbs could not have supported the body weight.
Basilosaurids, which had tiny hindlimbs and flipper-shaped forelimbs, were obligatory aquatic and came to dominate the oceans. They still lacked the echoloaction and balleen tooth of modern odontocetes and mysticeti. Basilosaurids and dorudontids are the oldest obligate aquatic cetaceans for which the entire skeleton is known. They display a number of aquatic adaptations not present in earlier archaeocetes: In the vertebral column, the neck vertebrae are short, the thoracic and lumbar vertebrae of similar length, the sacral vertebrae are unfused, the sacroiliac joints are absent, and the short tail has a ball vertebra (indicating the presence of a fluke). The scapulae are broad and fan-shaped with anterior acromions and small supraspinous fossae. The ulnae are large and have transversely flat olecranons, the wrists and distal forearms are flattened in the plane of the hands, and the hind limbs are tiny.
- Order Cetacea
- Suborder Archaeoceti
- Family Pakicetidae (Thewissen, Madar & Hussain 1996)
- Family Ambulocetidae (Thewissen, Madar & Hussain 1996)
- Family Remingtonocetidae (Kumar & Sahni 1986)
- Family Protocetidae
- Subfamily Georgiacetinae (Gingerich et al. 2005)
- Subfamily Makaracetinae (Gingerich et al. 2005)
- Subfamily Protocetinae (Gingerich et al. 2005)
- Genus Artiocetus (Gingerich et al. 2001)
- Genus Crenatocetus (McLeod & Barnes 2008)
- Genus Gaviacetus (Gingerich, Arif & Clyde 1995)
- Genus Indocetus (Sahni & Mishra 1975)
- Genus Maiacetus (Gingerich et al. 2009)
- Genus Protocetus (Fraas 1904)
- Genus Qaisracetus (Gingerich et al. 2001)
- Genus Rodhocetus (Gingerich et al. 1994)
- Genus Takracetus (Gingerich, Arif & Clyde 1995)
- Family Basilosauridae
- Subfamily Basilosaurinae
- Subfamily Dorudontinae
- Subfamily Kekenodontinae
- Subfamily Stromeriinae
- Suborder Archaeoceti
- Andrews, C. W. (1920). "A description of new species of zeuglodont and of leathery turtle from the Eocene of Southern Nigeria". Proceedings of the Zoological Society of London 1919 18: 309–19. OCLC 228169273. Retrieved April 2013.
- Bajpai, Sunil; Gingerich, Philip D (December 1998). "A new Eocene archaeocete (Mammalia, Cetacea) from India and the time of origin of whales". PNAS 95 (26): 15464–68. doi:10.1073/pnas.95.26.15464. OCLC 678707438.
- Bajpai, S; Thewissen, JG; Sahni, A (November 2009). "The origin and early evolution of whales: macroevolution documented on the Indian subcontinent". J Biosci 34 (5): 673–86. doi:10.1007/s12038-009-0060-0. OCLC 565869881. PMID 20009264. Retrieved February 2013.
- Dehm, Richard; Oettingen-Spielberg, Therese zu (1958). Paläontologische und geologische Untersuchungen im Tertiär von Pakistan. 2. Die mitteleocänen Säugetiere von Ganda Kas bei Basal in Nordwest-Pakistan. Abhandlungen / Neue Folge, 91. Munich: Beck. OCLC 163296508.
- Flower, William Henry (1883). "On the Arrangement of the Orders and Families of existing Mammalia". Proceedings of the Zoological Society of London: 178–86. OCLC 83091701.
- Fordyce, Ewan (2002). "Cetacean Evolution". In Perrin, William R; Wiirsig, Bernd; Thewissen, J G M. Encyclopedia of Marine Mammals. Academic Press. pp. 214–25. ISBN 0-12-551340-2.
- Fraas, E (1904). Neue Zeuglodonten aus dem unteren Mitteleozän von Mokattam bei Cairo 6 (3). Jena: Verlag Gustav Fischer. pp. 199–220.
- Geisler, Jonathan H; Sanders, Albert E; Luo, Zhe-Xi (July 2005). "A new protocetid whale (Cetacea, Archaeoceti) from the late middle Eocene of South Carolina". American Museum Novitates 3480: 1–68. doi:10.1206/0003-0082(2005)480[0001:ANPWCA]2.0.CO;2. OCLC 4630500767.
- Gingerich, Philip D; Haq, U; Khan, H; Zalmout, S (2001). "Eocene stratigraphy and archaeocete whales (Mammalia, Cetacea) of Drug Lahar in the eastern Sulaiman range, Balochistan (Pakistan)". Contributions from the Museum of Paleontology, University of Michigan 30 (11): 269–319. OCLC 50061585.
- Gingerich, Philip D; Haq, U; Zalmout, S; Khan, H; Malkani, S (September 2001). "Origin of whales from early artiodactyls: hands and feet of Eocene Protocetidae from Pakistan". Science 293 (5538): 2239–2242. Bibcode:2001Sci...293.2239G. doi:10.1126/science.1063902. ISSN 0036-8075. PMID 11567134.
- Gingerich, Philip D; Arif, M; Bhatti, M Akram; Anwar, M; Sanders, William J (1997). "Basilosaurus drazindai and Basiloterus hussaini, New Archaeoceti (Mammalia, Cetacea) from the Middle Eocene Drazinda Formation, with a Revised Interpretation of Ages of Whale-Bearing Strata in the Kirthar Group of the Sulaiman Range, Punjab (Pakistan)". Contributions from the Museum of Paleontology, University of Michigan 30 (2): 55–81. OCLC 742731913.
- Gingerich, Philip D (2007). "Stromerius nidensis, new archaeocete (Mammalia, Cetacea) from the Upper Eocene Qasr El-Sagha Formation, Fayum, Egypt". Contributions from the Museum of Paleontology 31 (13): 363–78. OCLC 214233870.
- Gingerich, Philip D.; Arif, Muhammad; Clyde, William C. (1995). "New Archaeocetes (Mammalia, Cetacea) from the middle Eocene Domanda Formation of the Sulaiman Range, Punjab (Pakistan)". Contributions from Museum of Paleontology, The University of Michigan 29 (11): 291–330. OCLC 34123868. Retrieved February 2013.
- Gingerich, Philip D.; Raza, S. M.; Arif, M.; Anwar, M.; Zhou, X. (1994). "New whale from the Eocene of Pakistan and the origin of cetacean swimming". Nature 368: 844–47. doi:10.1038/368844a0. OCLC 742745707. Retrieved April 2013.
- Gingerich, Philip D.; Russell, Donald E. (1981). "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). OCLC 742729300. Retrieved February 2013.
- Gingerich, Philip D.; ul-Haq, Munir; von Koenigswald, Wighart; Sanders, William J.; Smith, B. Holly; Zalmout, Iyad S. (2009). "New Protocetid Whale from the Middle Eocene of Pakistan: Birth on Land, Precocial Development, and Sexual Dimorphism". PLoS ONE 4 (2): e4366. doi:10.1371/journal.pone.0004366. OCLC 678622523. PMC 2629576.
- Gingerich, Philip D.; Zalmout, Iyad S.; Ul-Haq, Munir; Bhatti, M. Akram (2005). "Makaracetus bidens, a new protocetid archaeocete (Mammalia, Cetacea) from the early middle Eocene of Balochistan (Pakistan)". Contributions from the Museum of Paleontology 31 (9): 197–210. OCLC 742723177. Retrieved March 2013.
- Hulbert, Jr, Richard C; Petkewich, Richard M; Bishop, Gale A; Bukry, David; Aleshire, David P (September 1998). "A New Middle Eocene Protocetid Whale (Mammalia: Cetacea: Archaeoceti) and Associated Biota from Georgia". Journal of Paleontology 72 (5): 907–927. JSTOR 1306667. OCLC 4908698029.
- Kumar, K.; Sahni, A. (1986). "Remingtonocetus harudiensis, new combination, a middle Eocene archaeocete (Mammalia, Cetacea) from western Kutch, India". Journal of Vertebrate Paleontology 6 (4): 326–349. doi:10.1080/02724634.1986.10011629. OCLC 4649653943.
- McLeod, S. A.; Barnes, L. G. (2008). A new genus and species of Eocene protocetid archaeocete whale (Mammalia, Cetacea) from the Atlantic Coastal plain. In Wang, Xiaoming; Barnes, Lawrence G. "Geology and Vertebrate Paleontology of Western and Southern North America". Science Series, Natural History Museum of Los Angeles County 41. pp. 73–98. Retrieved February 2013.
- Rose, Kenneth David (2006). The Beginning of the Age of Mammals. JHU Press. ISBN 978-0-8018-8472-6.
- Sahni, Ashok; Mishra, Vijay Prakash (1975). "Lower Tertiary vertebrates from western India". Monograph of the PaleontologicalSociety of India 3: 1–48. ASIN B0007AL8UE. OCLC 3566369.
- Thewissen, JGM (2002). "Archaeocetes, Archaic". In Perrin, William R; Wiirsig, Bernd; Thewissen, J G M. Encyclopedia of Marine Mammals. Academic Press. pp. 36–9. ISBN 0-12-551340-2.
- Thewissen, J.G.M.; Hussain, S.T. (2000). "Attockicetus praecursor, a new remingtonocetid cetacean from marine Eocene sediments of Pakistan". Journal of Mammalian Evolution 7 (3): 133–46. doi:10.1023/A:1009458618729. OCLC 362777268.
- Thewissen, J. G. M.; Hussain, S. T. (1998). "Systematic review of the Pakicetidae, Early and middle Eocene Cetacea (Mammalia) from Pakistan and India". Bulletin of the Carnegie Museum 34: 220–38.
- Thewissen, J.G.M.; Madar, S.I.; Hussain, S.T. (1996). Ambulocetus natans, an Eocene cetacean (Mammalia) from Pakistan. Courier Forschungsinstitut Senckenberg 191. pp. 1–86. ISBN 9783929907322. OCLC 36463214.
- 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: 277–81. doi:10.1038/35095005. OCLC 118116179. Retrieved February 2013.
- Trivedy, A. N.; Satsangi, P. P. (1984). "A new archaeocete (whale) from the Eocene of India". Abstracts of 27th International Geological Congress, Moscow 1: 322–23.
- True, F.W. (1908). "The fossil cetacean, Dorudon serratus GIBBES. Bulletin of the Museum of Comparative Zoology". Bulletin of the Museum of Comparative Zoology 52 (4): 5–78. OCLC 355813868. OL 19219818M.
- Uhen, Mark D (1998). "New protocetid (Mammalia, Cetacea) from the late middle Eocene Cook Mountain Formation of Louisiana". Journal of Vertebrate Paleontology 18 (3): 664–8. OCLC 204612030.
- Uhen, Mark D; Gingerich, Philip D (January 2001). "New genus of dorudontine archaeocete (Cetacea) from the middle-to-late Eocene of South Carolina". Marine Mammal Science 17 (1): 1–34. doi:10.1111/j.1748-7692.2001.tb00979.x. OCLC 204061291.
- West, Robert M (1980). "Middle Eocene large mammal assemblage with Tethyan affinities, Ganda Kas region, Pakistan". Journal of Paleontology 54 (3): 508–533. JSTOR 1304193. OCLC 4899161959.