Limbs in whales and limblessness in other vertebrates: Mechanisms of evolutionary and developmental transformation and loss

Evolution and Development

Volumn 4, Issue 6, 2002, Pages 445-458

  Bejder, Lars ^a   Hall, Brian K ^a  

^a DALHOUSIE UNIVERSITY   (Canada)

Author keywords

[No Author keywords available]

Indexed keywords

EVOLUTION; LIMB; SNAKE; WHALE;

ANIMAL; EVOLUTION; GENE EXPRESSION REGULATION; GENETICS; HISTOLOGY; HOMEOBOX; LIMB; LIMB BUD; LIMB MALFORMATION; LIZARD; PHYLOGENY; PRENATAL DEVELOPMENT; REVIEW; SNAKE; WHALE;

ANIMALS; EVOLUTION; EXTREMITIES; GENE EXPRESSION REGULATION; GENES, HOMEOBOX; LIMB BUD; LIMB DEFORMITIES, CONGENITAL; LIZARDS; PHYLOGENY; SNAKES; WHALES;

ANIMALIA; CETACEA; DIGENEA (FLUKES); MAMMALIA; SERPENTES; SQUAMATA; TETRAPODA; VERTEBRATA;

EID: 0036860544     PISSN: 1520541X     EISSN: None     Source Type: Journal    
DOI: 10.1046/j.1525-142X.2002.02033.x     Document Type: Review

References (138)

1. Andrews, R. C. 1921. A remarkable case of external hind limb in a humpback whale. Am. Mus. Novitates 9: 1-9.
2. Arvy, L. 1979. The abdominal bones of cetaceans. In G. Pilleri G (ed.). Investigations on Cetacea. Vol. 10. Brain Anatomy Institute, Berne, Switzerland, pp. 215-227.
3. Atchley, W. R., and Hall, B. K. 1991. A model for development and evolution of complex morphological structures. Biol. Rev. Camb. Philos. Soc. 66: 101-157.
4. Bajpai, S., and Thewissen, J. G. M. 2000. A new, diminutive Eocene whale from Kachchh (Gujarat, India) and its implications for locomotor evolution of cetaceans. Curr. Sci. 79: 1478-1482.
5. Belting, H.-G., Shashikant, C. S., and Ruddle, F. H. 1998. Modification of expression and cis-regulation of Hoxc8 in the evolution of diverged axial morphology. Proc. Natl. Acad. Sci. US 95: 2355-2360.
6. Berta, A., and Sumich, J. L. 1999. Marine Mammals: Evolutionary Biology. Academic Press, San Diego.
7. Berzin, A. A. 1972. The Sperm Whale. Keter Press, Jerusalem.
8. Budd, G. E., and Jensen, S. 2000. A critical reappraisal of the fossil record of the bilaterian phyla. Biol. Rev. Camb. Philos. Soc. 75: 253-295.
9. Burke, A. C. 2000. Hox genes and the global patterning of the somitic mesoderm. Curr. Top. Dev. Biol. 47: 155-180.
10. Burke, A. C., Nelson, C. E., Morgan, B. A., and Tabin, C. 1995. Hox genes and the evolution of vertebrate axial morphology. Development 121: 333-346.
11. Caldwell, M. W. 1997. Limb osteology and ossification patterns in Cryptoclidus (Reptilia: Plesiosauroidea) with a review of Sauropterygian limbs. J. Vert. Paleontol. 17: 295-307.
12. Camp, C. L. 1923. Classification of the lizards. Bull. Am. Mus. Nat. Hist. 48: 298-481.
13. Carroll, R. L. 1988. Vertebrate Paleontology and Evolution. W. H. Freeman & Co., New York.
14. Carroll, S. B. 1995. Homeotic genes and the evolution of arthropods and chordates. Nature 376: 479-485.
15. Carroll, S. B. 2000. Endless forms: The evolution of gene regulation and morphological diversity. Cell 101: 577-580.
16. Chadwick, D. H. 2001. Evolution of whales. Natl. Geog. 200: 654-677.
17. Chevallier, A., Kieny, M., and Mauger, A. 1977. Limb-somite relationship: Origin of the limb musculature. J. Embryol. Exp. Morphol. 41: 245-258.
18. Christ, B., Jacob, H. J., and Jacob, M. 1977. Experimental analysis of the origin of the wing musculature in avian embryos. Anat. Embryol. 150: 171-186.
19. Coates, M. I. 1991. New palaeontological contributions to limb ontogeny and phylogeny. In J. R. Hinchliffe, J. M. Hurle, and D. Summerbell (eds.). Developmental Patterning of the Vertebrate Limb. Plenum Press, New York, pp. 325-337.
20. Coates, M. I., and Ruta, M. 2000. Nice snakes, shame about the legs. TREE 15: 503-507.
21. Cohn, M. J., Pate, K., Krumlauf, R., Wilkinson, D. G., Clarke, J. D. W., and Tickle, C. 1997. Hox9 genes and vertebrate limb specification. Nature 387: 97-101.
22. Cohn, M. J., and Tickle, C. 1999. Developmental basis of limblessness and axial patterning in snakes. Nature 399: 474-479.
23. Conway Morris S. 2000. Nipping the Cambrian "explosion" in the bud? Bio Essays 22: 1053-1056.
24. Cubo, J., and Arthur, W. 2001. Patterns of correlated character evolution in flightless birds: A phylogenetic approach. Evol. Ecol. 14: 693-703.
25. Deimer, P. 1977. Der rudimentäre hintere Extremitätengürtel des Pottwals (Physeter macrocephalus Linnaeus, 1758), seine Variabilität und Wachstumallometrie. Z. Saügertier. 42: 88-101.
26. Duboule, D., and Wilkins, A. S. 1998. The evolution of "bricolage." Trends Genet. 14: 54-59.
27. Essex, R. 1927. Studies in reptilian degeneration. Proc. Zool. Soc. Lond. 59: 879-945.
28. Felts, W. J. L., and Spurrell, F. A. 1966. Some structural and developmental characteristics of cetacean (odontocete) radii. A study of adaptive osteogenesis. Am. J. Anat. 118: 103-134.
29. Ferrari, D., Harrington, A., Dealy, C. N., and Kosher, R. A. 1999. Dlx-5 in limb initiation in the chick embryo. Dev. Dynam. 216: 10-15.
30. Fish, F. E. 1996. Transition from drag-based to lift-based propulsion in mammalian swimming. Am. Zool. 36: 628-641.
31. Fish, F. E. 1998. Biomechanical perspective on the origin of cetacean flukes. In J. G. M. Thewissen (ed.). The Emergence of Whales: Evolutionary Patterns in the Origin of Cetacea. Plenum Press, New York, pp. 303-324.
32. Fong, D. W., Kane, T. C., and Culver, D. C. 1995. Vestigialization and loss of nonfunctional characters. Annu. Rev. Ecol. Syst. 26: 249-268.
33. Gans, C. 1974. Biomechanics: An Approach to Vertebrate Biology. J. B. Lippincott, Philadelphia.
34. Gans, C. 1975. Tetrapod limblessness: Evolution and functional corollaries. Am. Zool. 15: 455-467.
35. Gatesy, J., and O'Leary, M. A. 2001. Deciphering whale origins with molecules and fossils. TREE 16: 562-570.
36. Gingerich, P. D., Smith, B. H., and Simons, E. L. 1990. Hind limbs of Eocene Basilosaurus: Evidence of feet in whales. Science 249: 154-157.
37. Gingerich, P. D., Wells, N. A., Russell, D. E., and Shah, S. M. I. 1983. Origin of whales in epicontinental remnant seas: New evidence from the early Eocene of Pakistan. Science 220: 403-406.
38. Gingerich, P. D., Raza, S. M., Arif, M., Anwar, M., and Zhou, X. 1994. New whale from the Eocene of Pakistan and the origin of cetacean swimming. Nature 368: 844-847.
39. Gingerich, P. D., and Uhen, M. 1996. Ancalecetus simonsi, a new dorudontine archaeocete (Mammalia, Cetacea) from the early late Eocene of Wadi Hitan, Egypt. Contrib. Mus. Paleont. Univ. Mich. 29: 359-401.
40. Gingerich, P. D., Haq, M., Zalmout, I. S., Khan, I. H., and Malkani, M. S. 2001. Origin of whales from early artiodactyls: Hands and feet of Eocene Protocetida from Pakistan. Science 293: 2239-2243.
41. Graham, A., and McGonnell, I. 1999. Developmental evolution: This side of paradise. Curr. Biol. 9: R630-R632.
42. Graur, D., and Higgins, D. G. 1994. Molecular evidence of the inclusion of cetaceans within the order Artiodactyla. Mol. Biol. Evol. 14: 537-364.
43. Greene, H. W., and Cundall, D. 2000. Limbless tetrapods and snakes with legs. Science 287: 1939-1941.
44. Greer, A. E. 1987. Limb reduction in the lizard genus Lerista. I. Variation in the number of phalanges and presacral vertebrae. J. Herpetol. 21: 267-276.
45. Guldberg, G., and Nansen, F. 1894. On the development and structure of the whale. Bergens Mus. 5: 1-70.
46. Haas, G. 1980. Pachyrhachis problematicus Haas, snakelike reptile from the Lower Cenomanian: Ventral view of skull. Bull. Mus. Natl. Hist. Nat. Paris 2: 87-104.
47. Hall, B. K. 1978. Developmental and Cellular Skeletal Biology. Academic Press, New York.
48. Hall, B. K. 1984. Developmental mechanisms underlying the formation of atavisms. Biol. Rev. Camb. Philos. Soc. 59: 89-124.
49. Hall, B. K. 1995. Atavisms and atavistic mutations: Evolutionary conservation of genetic and developmental information. Nat. Genet. 10: 126-127.
50. Hall, B. K. 1999. Evolutionary Developmental Biology. 2nd Ed. Kluwer Academic Publishers, Dordrecht, The Netherlands.
51. Hall, B. K. 2001. Development of the clavicles in birds and mammals. J. Exp. Zool. 289: 153-161.
52. Hall, B. K. 2002. Atavisms. In M. Pagel (ed.). Encyclopedia of Evolution. Vol. 1. Oxford University Press, New York, pp. 86-87.
53. Hall B. K. Palaeontology and evolutionary developmental biology: A science of the 19th and 21st centuries. Palaeontology 45: 647-649.
54. Hall, B. K. Descent with modification: The unity underlying homology and homoplasy as seen through an analysis of development and evolution. Biol. Rev. Camb. Philos. Soc. In Press.
55. Hall, B. K., and Miyake, T. 1995. Divide, accumulate, differentiate: Cell condensation in skeletal development revisited. Int. J. Dev. Biol. 39: 881-893.
56. Hall, B. K., and Miyake, T. 2000. All for one and one for all: Condensations and the initiation of skeletal development. Bio Essays 22: 138-147.
57. Hall, B. K., and Olson, W. M. (eds.). 2002. Key Concepts and Approaches in Evolutionary Developmental Biology. Harvard University Press, Cambridge, MA.
58. Hinchliffe, J. R. 1977. The development of winglessness (ws) in the chick embryo. Colloq. Int. C. N. R. S. Paris 266: 175-182.
59. Hofstetter, R., and Gasc, J. P. 1969. Vertebrae and ribs of modern reptiles. In C. Gans, A. d'A. Bellairs, and T. S. Parsons (eds.). Biology of the Reptilia. Vol. 1, No. 5. Academic Press, London, pp. 201-301.
60. Howell, A. B. 1970. Aquatic Mammals. Their Adaptation to Life in the Water. Dover Publications, New York. (a reprint of the 1930 edition).
61. Johnson, D. R. 1986. The Genetics of the Skeleton. Animal Models of Skeletal Development. Clarendon Press, Oxford.
62. Kenyon, K. W. 1969. The sea otter in the Eastern Pacific Ocean. North American Fauna, No. 68. US Bureau of Sport Fisheries and Wildlife, pp. 1-352.
63. Kieny, M. 1971. Les phases d'activité morphogènes du mésoderm somatopleural le développement précoce du membre chez l'embryon de poulet. Ann. Embryol. Morph. 4: 281-298.
64. Klima, M. 1990. Rudiments of the clavicle in the embryo of whales (Cetacea). Z. Saugetierkunde 55: 202-212.
65. Klima, M. 1992. Schwimmbewegungen und Auftauchmodusi bei Walen und bei Ichyhyosurien. Nat. Mus. 122: 1-17, 73-89.
66. Kükenthal, W. 1891. On the adaptation of mammals to aquatic life. Ann. Mag. Nat. Hist. Ser. 6, 7: 153-179.
67. Kükenthal, W. 1893. Vergleichend anatomische und entwicklungsgeschichtliche Untersuchung an Waltieren. Denkschridt der Medizinish-Naturwissenschaftlichen Gesellschaft zu Dritter Band, Jena.
68. Lamarck, J. B. 1984. Zoological Philosophy. An Exposition with Regard to the Natural History of Animals. Translated by Hugh Elliot, with introductory essays by D. L. Hull and R. W. Burkhardt, Jr. The University of Chicago Press, Chicago.
69. Lande, R. 1978. Evolutionary mechanisms of limb loss in tetrapods. Evolution 32: 73-92.
70. Lee, M. S. Y., and Caldwell, M. W. 1998. Anatomy and relationships of Pachyrhachis problematicus, a primitive snake with hindlimbs. Phil. Trans. R. Soc. Lond. Ser B 352: 1521-1552.
71. Lettice, L., Hecksher-Sørensen, J., and Hill, R. E. 1999. The dominant hemimelia mutation uncouples epithelial-mesenchymal interactions and disrupts anterior mesenchyme formation in mouse hindlimbs. Development 126: 4729-4736.
72. Luo, Z. 2000. In search of whale's sisters. Nature 404: 235-239.
73. Lyons, G., Krabbenhoft, K., Simandl, B. K., Buckingham, M., Fallon, J., and Robert, B. 1991. Hox-7: Temporal patterns of expression in normal and limbless chick embryos. In J. R. Hinchliffe, J. M. Hurle, and D. Summerbell (eds.). Developmental Patterning of the Vertebrate Limb. Plenum Press, New York, pp. 55-56.
74. Marshall, C. R., Raff, E. C., and Raff, R. A. 1994. Dollo's law and the death and resurrection of genes. Proc. Natl Acad. Sci. USA 91: 12283-12287.
75. Meyer, W., Neurand, K., and Klima, M. 1995. Prenatal development of the integument in Delphinidae (Cetacea: Odontoceti). J. Morphol. 223: 269-287.
76. Milinkovitch, M. C. 1995. Molecular phylogeny of cetaceans prompts revision of morphological transformations. TREE 10: 328-334.
77. Milinkovitch, M. C., Orti, G., and Meyer, A. 1993. Revised phylogeny of whales suggested by mitochondrial ribosomal DNA sequences. Nature 361: 346-348.
78. Milinkovitch, M. C., and Thewissen, J. G. M. 1997. Even-toed fingerprints on whale ancestry. Nature 388: 622-624.
79. Milaire, J. 1981. Les répercussions morphologiques du gène Dh (Dominant hememelia) sur les bourgeons de membres postérieurs et les constituants adjacens du tronc chez l'embryon de souris hétérozygote de 10 jours (stades de 32 h 43 métamères). Arch. Biol. 92: 95-138.
80. Miller, G. S. 1923. The telescoping of the cetacean skull. Smithsonian Misc. Coll. 76: 1-67.
81. M-Z Rahmani, T. 1974. Morphogenesis of the rudimentary hind-limb of the glass snake (Ophisaurus apodus Pallas). J. Embryol. Exp. Morphol. 32:431-443.
82. O'Leary, M. A. 1999. Parsimony analysis of total evidence from extinct and extant taxa and the Cetaeean-Artodactyl question (Mammalia, Ungulata). Cladistics 15: 315-330.
83. O'Leary, M. A. 2001. The phylogenetic position of Cetaceans: Further combined data analyses, comparisons with the stratigraphic record and a discussion of character optimization. Am. Zool. 41: 487-506.
84. O'Leary, M. A., and Geisler, J. H. 1999. The position of Cetacea within Mammalia: Phylogenetic analysis of morphological data from extinct and extant tax. Syst. Biol. 48: 455-490.
85. O'Leary, M. A., and Uhen, M. D. 1999. The time of origin of whales and the role of behavioral changes in the terrestrial-aquatic transition. Paleobiology 25: 534-556.
86. Omura, H. 1980. Morphological study of pelvic bones of the minke whale from the Antarctic. Sci. Rep. Whales Res. Inst. 32: 25-37.
87. Owen, R. 1842. Observations on the Basilosaurus of Dr. Harlan (Zeuglodon cetoides, Owen). Trans Geol. Soc. Lond. 6: 69-79.
88. Pabst, D., Rommel, S. A., and Mclellan, W. A. 1998. Evolution of thermoregulatory function in cetacean reproductive systems. In J. G. M. Thewissen (ed.). The Emergence of Whales: Evolutionary Patterns in the Origin of Cetacea. Plenum Press, New York, pp. 379-390.
89. Padian, K. 1992. A proposal to standardize phalangeal formula designations. J. Vert. Paleont. 12: 260-262.
90. Pena, M. R. C. 1967. Contribucion al conocimiento de la osteologia apendicular de Bipes (Reptilia: Amphisbaenia). Tesis Profesional, Inst Politec. Nac. Mexico.
91. Pinot, M. 1970. Le Rôle du mésoderm somitique dans la morphogenèse précoce des membres de l'embryon de Poulet. J. Embryol. Exp. Morphol. 23: 109-151.
92. Presch, W. 1975. The evolution of limb reduction in the teiid lizard genus Bachia. Bull. So. Calif. Acad. Sci. 74: 113-121.
93. Rage, J.-C., and Escuillié F. 2000. Un nouveau serpent bipède du Cénomanien (Crétacé). Implications phylétiques. C. R. Acad. Sci. Paris 330: 513-520.
94. Raynaud, A. 1990. Developmental mechanisms involved in the embryonic reduction of limbs in reptiles. Int. J. Dev. Biol. 34: 233-243.
95. Raynaud, A., and Kan, P. 1992. DNA synthesis decline involved in the developmental arrest of the limb bud in the embryo of the slow worm, Anguis gragilis (L.). Int. J. Dev. Biol. 36: 303-310.
96. Raynaud, A., Okuzumi, H., and Kouprach, S. 1974. Morphologie externe des stades précoces du développement des ébauches des membres du Lézard vert "Lacerta viridis Laur" et de l'Orvet "Anguis fragilis L", etudié au moyen de la microscopic électronique à balayage. Bull. Soc. Zool. France 99: 149-153.
97. Raynaud, A., and van den Elzen, P. 1976. La rudimentation des membres chez les embryons de Scelotes gronovii (Daudin), reptile scincidé Sud-Africain. Arch. Anat. Microsc. Morphol. Exp. 65: 17-36.
98. Rieppel, O. 1988. A review of the origin of snakes. Evol. Biol. 22: 37-130.
99. Robert, B., Lyons, G, Simandl, B. K., Kuroiwa, A., and Buckingham, M. 1991. The apical ectodermal ridge regulates Hox-7 and Hox-8 gene expression in developing chick limb buds. Genes Dev. 5: 2363-2374.
100. Rommel, S. A. 1990. Osteology of the bottlenose dolphin. In S. R. Leatherwood and R. R. Reeves (eds.). The Bottlenose Dolphin. Academic Press, San Diego, pp. 29-49.
101. Rosa-Molinar, E., and Burke, A. C. 2002. Starting from fins: Parallelism in the evolution of limbs and genitalia: The fin-to-genitalia transition. Evol. Dev. 4: 124-126.
102. Schneider, R. A., Hu, D., and Helms, J. A. 1999. From head to toe: Conservation of molecular signals regulating limb and craniofacial morphogenesis. Cell Tissue Res. 296: 103-109.
103. Sedmera, D., Misek, I., and Klima, M. 1997a. On the development of cetacean extremities. I. Hind limb rudimentation in the spotted dolphin (Stenella attenuata). Eur. J. Morphol. 35: 25-30.
104. Sedmera, D., Misek, I., and Klima, M. 1997b. On the development of cetacean extremities. II. Morphogenesis and histogenesis of the flippers in the spotted dolphin (Stenella attenuata). Eur. J. Morphol. 35:117-123.
105. Shapiro, M. D. Developmental morphology of limb reduction in Hemiergis (Squamata: Scincidae): Chondrogenesis, osteogenesis, and heterochrony. J. Morphol. In Press.
106. Shapiro, M. D., and Carl, T. F. 2001. Novel features of tetrapod limb development in two nontraditional model species: A skink and a direct-developing frog. In M. L. Zelditch (ed.). Beyond Heterochrony. The Evolution of Development. Wiley-Liss, New York, pp. 337-361.
107. Shashikant, C. S., Kim, C. B., Borbély, M. A., Wang, W. C. H., and Ruddle, F. H. 1998. Comparative studies on mammalian Hoxc8 early enhancer sequence reveal a baleen whale-specific deletion of a cis-acting element. Proc. Natl Acad. Sci. USA 95: 15446-15451.
108. Shimamura, M., Yasue, H., Ohshima, K., Abe, H., Kato, H., Kishiro, T., Goto, M., Munechika, I., and Okada, N. 1997. Molecular evidence from retroposons that whales form a clade within the even-toed ungulates. Nature 88: 666-670.
109. Shubin, N., Tabin, C., and Carroll, B. B. 1997. Fossils, genes and the evolution of animal limbs. Nature 388: 639-648.
110. Slijper, E. J. 1979. Whales. Cornell University Press, Ithaca.
111. Smith, K. K., and Schneider, R. A. 1998. Have gene knockouts caused evolutionary reversals in the mammalian first arch? Bio Essays 20: 245-255.
112. Spoor, F., Bajpai, S. T., Hussain, K., and Thewissen, J. G. M. 2002. Vestibular evidence for the evolution of aquatic behaviour in early cetaceans. Nature 417: 163-166.
113. Sterba, O., Klima, M., and Schlidger, B. 1994. Proportional growth of dolphins during the prenatal period. Funct. Dev. Morphol. 4: 282-283.
114. Sterba, O., Klima, M., and Schlidger, B. 2000. Embryology of dolphins. Staging and ageing of embryos and fetuses of some cetaceans. Adv. Anat. Embryol. Cell Biol. 157: 1-133.
115. Stokeley, P. S. 1947. Limblessness and correlated changes in the girdles of a comparative morphological series of lizards. Am. Midl. Nat. 38: 725-754.
116. Struthers, J. 1881. On the bones, articulations, and muscles of the rudimentary hind-limb of the Greenland Right-whale (Balaena mysticetus). J. Anat. Physiol. 15: 141-176, 302-321.
117. Szalay, F. 1969. The Hapalodectinae and a phylogeny of the Mesonychidae (Mammalia, Condylartha). Am. Mus. Nov. 2361: 1-26.
118. Tautz, D. 2000. Evolution of transcriptional regulation. Curr. Opin. Genet. Dev. 10: 575-579.
119. Tchernov, E., Rieppel, O., Zaher, H., Polcyn, M. J., and Jacobs, L. L. 2000. A fossil snake with limbs. Science 287: 2010-2012.
120. Thewissen, J. G. M. (ed.). 1998. The Emergence of Whales: Evolutionary Patterns in the Origin of Cetacea. Plenum Press, New York.
121. Thewissen, J. G. M., and Bajpai, S. 2001. Whale origins as a poster child for macroevolution. BioScience 51: 1037-1049.
122. Thewissen, J. G. M., and Fish, F. E. 1997. Locomotor evolution in earliest cetaceans: Functional model, modern analogues, and paleontologic evidence. Paleobiology 23: 482-490.
123. Thewissen, J. G. M., and Hussain, S. T. 1993. Origin of underwater hearing in whales. Nature 361: 444-445.
124. Thewissen, J. G. M., Hussain, S, T., and Arif, M. 1994. Fossil evidence for the origin of aquatic locomotion in archaeocete whales. Science 263: 210-212.
125. Thewissen, J. G. M., Madar, S. I., and Hussain, S. T. 1998. Whale ankles and evolutionary relationships. Nature 395: 452.
126. Thewissen, J. G. M., Williams, T. M., Roe, L. J., and Hussain, S. T. 2001. Skeletons of terrestrial cetaceans and the relationship of whales to artiodactyls. Nature 413: 277-281.
127. Uhen, M. 1998. Middle to late Eocene basilosaurines and dorudontines. In J. G. M. Thewissen (ed.). The Emergence of Whales: Evolutionary Patterns in the Origin of Cetacea. Plenum Press, New York, pp. 29-61.
128. Uhen, M. D., and Gingerich, P. D. 2001. New genus of dorudontine Archaeocete (Cetacea) from the middle-to late Eocene of South Carolina. Mar. Mamm. Sci. 17: 1-34.
129. van der Schoot, P. 1995. Studies on the fetal development of the gubernaculum in cetacea. Anat. Rec. 243: 449-460.
130. Van Valen, L. 1968. Monophyly or diphyly in the origin of whales. Evolution 22: 37-41.
131. Van Valen, L. 1973. A new evolutionary law. Evol. Theory 1: 1-30.
132. Vassé, J. 1974. Etudes expérimentales sur le rôle des somites au cours des premiers stades du développement du membre antérieur chez l'embryon du chélonien, Emys orbicularis L. J. Embryol. Exp. Morphol. 32: 417-430.
133. Vassé J. 1977. Etudes expérimentales sur les premiers stades du développement du membre antérieur chez l'embryon du chélonien, Emys orbicularis L: Détermination en mosaïque et régulation. J. Embryol. Exp. Morphol. 42: 135-148.
134. Wartzok, D., and Ketten, D. R. 1999. Marine Mammal Sensory Systems. In J. E. Reynolds and S. A. Rommel (eds.). Biology of Marine Mammals. Smithsonian Institution Press, Washington, DC, pp. 117-175.
135. Weihs, D. 1989. Design features and mechanics of axial locomotion in fish. Am. Zool. 29: 151-160.
136. Williams, T. M. 1989. Swimming by sea otters: Adaptations for low energetic cost locomotion. J. Comp. Physiol. A 164: 815-824.
137. Wong, K. 2002. The mammals that conquered the seas. Sci. Am. 286: 70-79.
138. Yablokov, A. V. 1974. Variability of Mammals. Amerind Publishing Co., New Delhi.