There have been very few studies of brain size and encephalization in cetaceans and essentially none that have made direct quantitative comparisons of cetaceans and another mammalian group using large normative samples. In the present study two different measures of encephalization were calculated and used to rank and compare 21 odontocete species and 60 anthropoid primate species. Comparisons were made both within and between the two groups. Results show that the encephalization level of Homo sapiens is still extraordinary relative to that of nonhuman species. Nevertheless, a subset of delphinid odontocetes are significantly more highly encephalized than the most highly encephalized anthropoid primates and narrow the gap in encephalization between humans and nonhumans substantially. These findings may have implications for comparative models of the relative importance of brain size versus brain organization for the evolution of intelligence.

Keywords:
Encephalization, Brain size, Brain evolution, Cetaceans, Odontocetes, Primates
1.
Armstrong, E. (1982) A look at relative brain size in mammals. Neurosci. Lett., 34: 101–104.
2.
Armstrong, E. (1983) Relative brain size and metabolism in mammals. Science, 220: 1302–1304.
3.
Armstrong, E. (1985) Allometric considerations of the adult mammalian brain with special emphasis on primates. In Size and Scaling in Primate Biology (ed. by W.J. Jungers), Plenum Press, New York, London, pp. 115–146.
4.
Bauchot, R., and H. Stephan (1969) Encéphalisation et niveau évolutif chez les simiens. Mammalia, 33: 235–275.
5.
Best, R.C., and V.M. da Silva (1989) Amazon River dolphin, Boto Inia geoffrensis (de Blainville, 1817). In Handbook of Marine Mammals, Vol. 4: River Dolphins and the Larger Toothed Whales (ed. by S.H. Ridgway and R. Harrison), Academic Press, New York, pp. 1–24.
6.
Bronson, R.T. (1981) Brain weight-body weight relationships in twelve pieces of nonhuman primates. Am. J. Phys. Anthropol., 56: 77–81.
7.
Bryden, M.M. (1986) Age and growth. In Research on Dolphins (ed. by M.M. Bryden and R. Harrison), Clarendon Press, Oxford, pp. 211–224.
8.
Chen, I. (1979) On the cerebral anatomy of Chinese river dolphin, Lipotes vexillifer. Acta Hydrobiol. Sinica, 6: 366–372.
9.
Crile, G., and D.P. Quiring (1940) A record of the body weight and certain organ and gland weights of 3,690 animals. Ohio J. Sci., XL(5): 219–389.
10.
Eisenberg, J.F., and D.E. Wilson (1978) Relative brain size and feeding strategies in the Chiroptera. Evolution, 32: 740–751.
11.
Eisenberg, J.F., and D.E. Wilson (1981) Relative brain size and demographic strategies in didelphid marsupials. Am. Nat., 118: 1–15.
12.
Gjukic, M. (1995) Ein Beitrag zum Problem der Korrelation zwischen Hirngewicht und Körpergewicht. Z. Morphol. Anthropol., 47: 43–57.
13.
Glezer, I., M.S. Jacobs, and P.J. Morgane (1988) Implications of the ‘initial brain’ concept for brain evolution in Cetacea. Behav. Brain Sci., 11: 75–116.
14.
Harvey, P., and J.R. Krebs (1990) Comparing brains. Science, 249: 140–146.
15.
Hay, K., and A. Mansfield (1989) Narwahl (Monodon monoceros Linnaeus, 1758). In Handbook of marine mammals, Vol. 4: River Dolphins and the Larger Toothed Whales (ed. by S. Ridgway and R. Harrison), Academic Press, New York, pp. 145–176.
16.
Hofman, M.A. (1982) Encephalization in mammals in relation to the size of the cerebral cortex. Brain Behav. Evol., 20: 84–96.
17.
Hofman, M.A. (1983) Energy metabolism, brain size and longevity in mammals. Q. Rev. Biol., 58: 496–512.
18.
Holloway, R.L. (1980) Within-species brain-body weight variability: a re-examination of the Danish data and other primate species. Am. J. Phys. Anthropol., 53: 109–121.
19.
Hrdlicka, A. (1925) Weight of the brain and of the internal organs in American monkeys. Am. J. Phys. Anthropol., 8(2): 201–211.
20.
Jansen, J., and J.K. Jansen (1969) The nervous system of Cetacea. In Biology of Marine Mammals (ed. by H. Anderson), Academic Press, New York, pp. 175–252.
21.
Jerison, H.J. (1955) Brain to body ratios and the evolution of intelligence. Science, 121: 447–449.
22.
Jerison, H.J. (1963) Interpreting the evolution of the brain. Human Biol., 35: 263–291.
23.
Jerison, H.J. (1973) Evolution of the Brain and Intelligence. Academic Press, New York, N.Y.
24.
Jerison, H.J. (1978) Brain and intelligence in whales. In Whales and Whaling: Vol. 2 (ed. by S. Frost), C.J. Thompson, Australian Commonwealth Government Printer, Canberra, pp. 159–197.
25.
Kamiya, T., and F. Yamasaki (1974) Organ weights of Pontoporia vlainvillei and Platanista gangetica (Plastanistidae). Scientific Reports of the Whale Research Institute, 32: 105–126.
26.
Kruger, L. (1959) The thalamus of the dolphin Tursiops truncatus and comparison with other mammals. J. Comp. Neurol., 3: 133–194.
27.
Laird, A. (1969) The dynamics of growth. Res. Dev., 20: 28–31.
28.
Leatherwood, S., and R.R. Reeves (1990) The Bottlenose Dolphin. Academic Press, London.
29.
Mace, G.M., P.H. Harvey, and T.H. Clutton-Brock (1980) Is brain size and ecological variable? Trends Neurosci., 3: 193–196.
30.
Marino, L. (1995) Brain-behavior relationships in cetaceans and primates: implications for the evolution of complex intelligence. Ph.D. dissertation, State University of New York, University at Albany, Albany, New York.
31.
Marino, L. (1997) The relationship between gestation length, encephalization, and body weight in odontocetes. Marine Mammal Sci., 13(1): 133–138.
32.
Martin, R. (1981) Relative brain size and basal metabolic rate in terrestrial vertebrates. Nature, 293: 60–67.
33.
McNab, B.K., and J.F. Eisenberg (1989) Brain size and its relation to the rate of metabolism in mammals. Am. Nat., 133(2): 157–167.
34.
Morgane, P.J., and M.S. Jacobs (1972) Comparative anatomy of the cetacean nervous system. In Functional Anatomy of Marine Mammals, Vol. 1 (ed. by R.J. Harrison), Academic Press, London, pp. 118–244.
35.
Morgane, P.J., M.S. Jacobs, and W.L. McFarland (1980) The anatomy of the brain of the bottlenose dolphin (Tursiops truncatus). Surface configurations of telencephalon of the bottlenose dolphin with comparative anatomical observations in four other cetacean species. Brain Res. Bull., 5(3): 1–108.
36.
Pagel, M., and P. Harvey (1989) Taxonomic differences in the scaling of brain on body weight among mammals. Science, 244: 1589–1593.
37.
Napier, J.R., and P.H. Napier (1967) A Handbook of Living Primates. Academic Press, London.
38.
Passingham, R.E. (1975) The brain and intelligence. Brain Behav. Evol., 11: 1–15.
39.
Pilleri, G., and R. Busnel (1969) Brain/body weight ratios in Delphinidae. Acta Anat., 51: 241–258.
40.
Pilleri, G., and M. Gihr (1968) On the brain of the Amazon dolphin Inia geoffrensis de Blainville, 1817 (Cetacea Susuidae). Experientia, 24: 932–934.
41.
Pilleri, G., and M. Gihr (1970a) The central nervous system of the Mysticete and Odontocete whales. Invest. Cetacea, 2: 87–135.
42.
Pilleri, G., and M. Gihr (1970b) Brain-body weight ratio of Platanista gangetica. Invest. Cetacea, 2: 79–82.
43.
Pirlot, P., and T. Kamiya (1975) Comparison of ontogenetic brain growth in marine and coastal dolphins. Growth, 39: 507–525.
44.
Radinsky, L. (1967) Relative brain size: a new measure. Science, 155: 836–837.
45.
Ridgway, S.H. (1972) Mammals of the Sea: Biology and Medicine. Thomas, Springfield.
46.
Ridgway, S.H. (1990) The central nervous system of the bottlenose dolphin. In The Bottlenose Dolphin (ed. by S. Leatherwood and R.R. Reeves), Academic Press, San Diego, California, pp. 69–100.
47.
Ridgway, S.H., and R.H. Brownson (1979) Brain size and symmetry in three dolphin genera. Anat. Rec., 193: 664.
48.
Ridgway, S.H., and R.H. Brownson (1984) Relative brain sizes and cortical surface areas in odontocetes. Acta Zool. Fennica, 172: 149–152.
49.
Ridgway, S.H., L.S. Demski, T.H. Bullock, and M. Schwanzel-Fukuda (1987) The terminal nerve in odontocete cetaceans. Ann. New York Acad. Sci., 519: 201–212.
50.
Ridgway, S.H., N. Flanigan, and J. McCormick (1966) Brain-spinal cord ratios in porpoises: possible correlations with intelligence and ecology. Psychonomic Sci., 6(11): 491–492.
51.
Schultz, A.H. (1950) Morphological observations on gorillas. In The Anatomy of the Gorilla (ed. by W.K. Gregory), Columbia University Press, New York, pp. 228–253.
52.
Stephan, H., G. Baron, and H. Frahm (1988) Comparative size of brains and brain components. In Comparative Primate Biology, Vol. 4: Neurosciences (ed. by H. Steklis and J. Erwin), Alan R. Liss, New York, pp. 1–38.
53.
Stephan, H., R. Bauchot, and O. Andy (1970) Data on size of the brain and of various brain parts in insectivores and primates. In The Primate Brain: Advances in Primatology, Vol. 1 (ed. by C.R. Noback and W. Montagna), Appleton-Century-Crofts, New York, pp. 289–298.
54.
Stephan, H., H. Frahm, and G. Baron (1981) New and revised data on volume of brain structures in insectivores and primates. Folia Primatol., 35: 1–29.
55.
Tylinek, E., and G. Berger (1985) Monkeys and Apes. Arco Publishing, Inc., New York.
56.
von Bonin, G. (1936) Brain-weight and body-weight of mammals. J. Gen. Psychol., 16: 379–389.
57.
Wood, F.G., and W.E. Evans (1980) Adaptiveness and ecology of echolocation in toothed whales. In Animal Sonar Systems (ed. by R. Busnel and J. Fish), Plenum Press, New York, pp. 381–426.
58.
Worthy, G.A., and J.P. Hickie (1986) Relative brain size in marine mammals. Am. Nat., 128: 445–459.
1998
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