The earliest known fully quadrupedal sirenian

Abstract

Modern seacows (manatees and dugongs; Mammalia, Sirenia) are completely aquatic, with flipperlike forelimbs and no hindlimbs1,2. Here I describe Eocene fossils from Jamaica that represent nearly the entire skeleton of a new genus and species of sirenian—the most primitive for which extensive postcranial remains are known. This animal was fully capable of locomotion on land, with four well-developed legs, a multivertebral sacrum, and a strong sacroiliac articulation that could support the weight of the body out of water as in land mammals. Aquatic adaptations show, however, that it probably spent most of its time in the water. Its intermediate form thus illustrates the evolutionary transition between terrestrial and aquatic life. Similar to contemporary primitive cetaceans3, it probably swam by spinal extension with simultaneous pelvic paddling, unlike later sirenians and cetaceans, which lost the hindlimbs and enlarged the tail to serve as the main propulsive organ. Together with fossils of later sirenians elsewhere in the world1,4,5,6,7, these new specimens document one of the most marked examples of morphological evolution in the vertebrate fossil record.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.

from$8.99

All prices are NET prices.

Figure 1: Reconstructed composite skeleton of Pezosiren portelli.
Figure 2: Pezosiren portelli.

References

  1. 1

    Domning, D. P. The readaptation of Eocene sirenians to life in water. Hist. Biol. 14, 115–119 (2000).

  2. 2

    Domning, D. P. in Secondary Adaptation of Tetrapods to Life in Water (eds Mazin, J.-M. & de Buffrénil, V.) 151–168 (Dr Friedrich Pfeil, Munich, 2001).

  3. 3

    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).

  4. 4

    Domning, D. P. & Gingerich, P. D. Protosiren smithae, new species (Mammalia, Sirenia), from the late Middle Eocene of Wadi Hitan, Egypt. Contr. Mus. Paleontol. Univ. Michigan 29, 69–87 (1994).

  5. 5

    Siegfried, P. Das Femur von Eotheroides libyca (Owen) (Sirenia). Palaeontol. Zs. 41, 165–172 (1967).

  6. 6

    Lepsius, G. R. Halitherium schinzi, die fossile Sirene des Mainzer Beckens. Abh. Mittelrheinischen Geol. Ver. 1, 1–200 (1882).

  7. 7

    Abel, O. Die Sirenen der mediterranen Tertiärbildungen Österreichs. Abh. Geol. Reichsanst. Wien 19, 1–223 (1904).

  8. 8

    Domning, D. P., Emry, R. J., Portell, R. W., Donovan, S. K. & Schindler, K. S. Oldest West Indian land mammal: rhinocerotoid ungulate from the Eocene of Jamaica. J. Vertebr. Paleontol. 17, 638–641 (1997).

  9. 9

    Pregill, G. K. Eocene lizard from Jamaica. Herpetologica 55, 157–161 (1999).

  10. 10

    MacPhee, R. D. E., Flemming, C., Domning, D. P., Portell, R. W., & Beatty, B. Eocene ?primate petrosal from Jamaica: morphology and biogeographical implications. J. Vertebr. Paleontol. 19 (Suppl.), 61A (1999).

  11. 11

    Domning, D. P. A phylogenetic analysis of the Sirenia. Proc. San Diego Soc. Nat. Hist. 29, 177–189 (1994).

  12. 12

    Domning, D. P., Morgan, G. S., & Ray, C. E. North American Eocene sea cows (Mammalia: Sirenia). Smithson. Contr. Paleobiol. 52, 1–69 (1982).

  13. 13

    Matthew, W. D. Paleocene faunas of the San Juan Basin, New Mexico. Trans. Am. Phil. Soc. 30, 1–510 (1937).

  14. 14

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

  15. 15

    Domning, D. P. Supposedly unique features of the desmostylian tibia are also found in other mammals. Bull. Ashoro Mus. Paleontol. 2, 39–42 (2001).

  16. 16

    Thewissen, J. G. M. & Domning, D. P. The role of phenacodontids in the origin of the modern orders of ungulate mammals. J. Vertebr. Paleontol. 12, 494–504 (1992).

  17. 17

    Liu, F. R. & Miyamoto, M. M. Phylogenetic assessment of molecular and morphological data for eutherian mammals. Syst. Biol. 48, 54–64 (1999).

  18. 18

    Savage, R. J. G., Domning, D. P. & Thewissen, J. G. M. Fossil Sirenia of the West Atlantic and Caribbean region. V. The most primitive known sirenian, Prorastomus sirenoides Owen, 1855. J. Vertebr. Paleontol. 14, 427–449 (1994).

  19. 19

    Domning, D. P. & de Buffrénil, V. Hydrostasis in the Sirenia: quantitative data and functional interpretations. Mar. Mamm. Sci. 7, 331–368 (1991).

  20. 20

    Taylor, M. A. Functional significance of bone ballast in the evolution of buoyancy control strategies by aquatic tetrapods. Hist. Biol. 14, 15–331 (2000).

  21. 21

    Fish, F. E. Transitions from drag-based to lift-based propulsion in mammalian swimming. Am. Zool. 36, 628–641 (1996).

  22. 22

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

Download references

Acknowledgements

I thank J. Bailey, B. Beatty, D. Da Silva, H. Dixon, S. K. Donovan, R. J. Emry, C. Flemming, F. Grady, H. and J. Halvorson, J. Herrera, K. Hickey-Commins, S. Hutchens, S. Jabo, D. Jones, I. A. Koretsky, J. Kramer, B. J. MacFadden, C. MacGillivray, R. D. E. MacPhee, S. Mitchell, R. W. Portell, T. Radenbaugh, K. S. Schindler, T. A. Stemann, C. Terranova, and B., R. and J. Toomey. Field work was funded by the National Geographic Society; B. and R. Toomey; the Potomac Museum Group; the University of the West Indies; the American Museum of Natural History; and R. Liberman.

Author information

Correspondence to D. P. Domning.

Rights and permissions

Reprints and Permissions

About this article

Further reading

Comments

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.