Fossil evidence for the origin of aquatic locomotion in archaeocete whales

Science

Volumn 263, Issue 5144, 1994, Pages 210-212

  Thewissen, J G M ^a   Hussain, S T ^b   Arif, M ^c  

^a NORTHEAST OHIO MEDICAL UNIVERSITY   (United States)

^b HOWARD UNIVERSITY   (United States)

^c Geological Survey of Pakistan   (Pakistan)

Author keywords

[No Author keywords available]

Indexed keywords

ARCHAEOCETE; LOCOMOTION; MAMMAL; MORPHOLOGY; WHALE;

EID: 0028182149     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.263.5144.210     Document Type: Article

References (28)

1. R. M. West, J. Paleontol. 54, 508 (1980).
2. J. G. M. Thewissen and S. T. Hussain, Nature 361, 444 (1993).
3. Order Cetacea, Suborder Archaeoceti, Family Protocetidae. Ambulocetus natans, n. gen., n. sp. Holotype. Howard Geological Survey of Pakistan 18507: skull with left P4/-M1-2/ and lacking the rostrum, but preserving both tympanics, basihyoid, right posterior mandible with P/4, M/2-3, and left ramus with alveoli for C/1-P/3, half atlas, fragments of three other cervical vertebrae, two complete and several fragmentary thoracic and one lumbar vertebra, three complete ribs, and a sternebra. Forelimb fragments include part of the glenoid, left and right radius and ulna, all left carpals except the triquetrum, all metacarpals, and at least four proximal, two intermediate phalanges, and a fragment of one distal phalanx. Hindlimb elements include complete femur, proximal tibia, distal fibula, trochlea of astragalus, metatarsals II-V and at least two proximal, three intermediate, and three distal phalanges. The holotype was found at locality HGSP 9209 in the upper Kuldana Formation, Punjab, 3.7 km northwest of Ganda Kas (72°12′20″E, 33°39′N). Referred material. P/2 (HGSP 18473), P/3 (HGSP 18497), caudal vertebra (HGSP 18472), and distal femur (HGSP 18476), all from locality 9207, about 5 m above the type locality in the section. All material will be housed at the Geological Survey of Pakistan in Islamabad. Known distribution. Kala Chitta Hills of Pakistan, upper Kuldana Formation and transitional beds to the Kohat Formation. Lower to middle Eocene. Differential diagnosis of genus. P4/ of Ambulocetus has a single high labial cusp, unlike Protocetus (16), but lacks a protocone. M1/ and M2/ of Ambulocetus are similar in morphology, bearing a high and connate para- and metacone, and a protocone that is on a broad and low lingual shelf, unlike remingtonocetids where this shelf is narrow. The protocone of Ambulocetus is weaker than that of Pakicetus (1) and Ichthyolestes [R. Dehm and T. zu Oettingen-Spielberg, Bayer. Akad. Wiss. Math. Naturwiss. Kl. Abh. 91, 1 (1958)], while the cusp is absent in Protocetus. This cusp is well set off from the labial cusps, unlike Indocetus. Crests are poorly developed on the teeth of Ambulocetus, as in their mesonychid ancestors [F. S. Szalay, Evolution 23, 703 (1969)]. The lower canine is large and single rooted, whereas the four lower premolars have two roots, unlike remingtonocetids. P/4 consists of a single high cusp, unlike Pakicetus. The trigonid of M/2 and M/3 is much higher than the talonid, unlike Gandakasia and Pappocetus (15). It lacks a metaconid, unlike Pakicetus. Ambulocetus lacks the tubercles that occur rostral to the protoconid of Pappocetus. Few details of the talonid remain, but there seems to have been a single cusp and no basin, as in Pakicetus. Unlike most other archaeocetes, the pterygoid processes are enormous and their dorsoventral extent matches that of the braincase. Etymology. The genus name is a combination of ambulare (to walk) and cetus (whale), in recognition of a characteristic mode of locomotion in this cetacean. The species indication, natans (swimming), describes another aspect of its locomotor repertoire.
4. Order Cetacea, Suborder Archaeoceti, Family Protocetidae. Ambulocetus natans, n. gen., n. sp. Holotype. Howard Geological Survey of Pakistan 18507: skull with left P4/-M1-2/ and lacking the rostrum, but preserving both tympanics, basihyoid, right posterior mandible with P/4, M/2-3, and left ramus with alveoli for C/1-P/3, half atlas, fragments of three other cervical vertebrae, two complete and several fragmentary thoracic and one lumbar vertebra, three complete ribs, and a sternebra. Forelimb fragments include part of the glenoid, left and right radius and ulna, all left carpals except the triquetrum, all metacarpals, and at least four proximal, two intermediate phalanges, and a fragment of one distal phalanx. Hindlimb elements include complete femur, proximal tibia, distal fibula, trochlea of astragalus, metatarsals II-V and at least two proximal, three intermediate, and three distal phalanges. The holotype was found at locality HGSP 9209 in the upper Kuldana Formation, Punjab, 3.7 km northwest of Ganda Kas (72°12′20″E, 33°39′N). Referred material. P/2 (HGSP 18473), P/3 (HGSP 18497), caudal vertebra (HGSP 18472), and distal femur (HGSP 18476), all from locality 9207, about 5 m above the type locality in the section. All material will be housed at the Geological Survey of Pakistan in Islamabad. Known distribution. Kala Chitta Hills of Pakistan, upper Kuldana Formation and transitional beds to the Kohat Formation. Lower to middle Eocene. Differential diagnosis of genus. P4/ of Ambulocetus has a single high labial cusp, unlike Protocetus (16), but lacks a protocone. M1/ and M2/ of Ambulocetus are similar in morphology, bearing a high and connate para- and metacone, and a protocone that is on a broad and low lingual shelf, unlike remingtonocetids where this shelf is narrow. The protocone of Ambulocetus is weaker than that of Pakicetus (1) and Ichthyolestes [R. Dehm and T. zu Oettingen-Spielberg, Bayer. Akad. Wiss. Math. Naturwiss. Kl. Abh. 91, 1 (1958)], while the cusp is absent in Protocetus. This cusp is well set off from the labial cusps, unlike Indocetus. Crests are poorly developed on the teeth of Ambulocetus, as in their mesonychid ancestors [F. S. Szalay, Evolution 23, 703 (1969)]. The lower canine is large and single rooted, whereas the four lower premolars have two roots, unlike remingtonocetids. P/4 consists of a single high cusp, unlike Pakicetus. The trigonid of M/2 and M/3 is much higher than the talonid, unlike Gandakasia and Pappocetus (15). It lacks a metaconid, unlike Pakicetus. Ambulocetus lacks the tubercles that occur rostral to the protoconid of Pappocetus. Few details of the talonid remain, but there seems to have been a single cusp and no basin, as in Pakicetus. Unlike most other archaeocetes, the pterygoid processes are enormous and their dorsoventral extent matches that of the braincase. Etymology. The genus name is a combination of ambulare (to walk) and cetus (whale), in recognition of a characteristic mode of locomotion in this cetacean. The species indication, natans (swimming), describes another aspect of its locomotor repertoire.
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28. We thank A. Aslan, D. P. Domning, F. E. Fish, R. E. Fordyce, P. D. Gingerich, R. C. Hulbert, S. I. Madar, S. M. Raza, K. D. Rose, A. R. Wyss, and the Geological Survey of Pakistan. Field work was supported by the National Geographic Society.