Abstract

(…) Brody (1945) fitted an allometric equation to heart mass (kg) as a function of body mass (kg) for adult mammals ranging in body size from 0.01 to over 100,000 kg. Innes et al. (1986) observed that the mass exponent in Brody’s equation H = 0 00588M^0.984 where H is heart mass and M is body mass, is not different from 0.94 derived for cetacean species (Sergeant’s data 1969). Lockyer (1981) also showed that Brody’s equation seems to fit heart mass data for cetaceans as different as Phocoena phocoena and Balaenoptera musculus. Ridgway and Johnston (1966), however, reported differences in heart mass as a percent of body mass between the three species Phocoenoides dalli, Lagenorhynchus obliquidens and Tursiops truncatus. Heart mass estimates made from a general allometric equation such as Brody’s or Innes’s will fail to demonstrate differences in heart masses, if they do exist, between species whose body sizes overlap. Limiting the range of body sizes over which these equations are fit may provide insight into physiological, morphological, or behavioral variation between species (Smith 1984). We present heart mass and body mass values from three genera of small odontocetes in which interspecific differences in scaling do exist, and propose an explanation based on ecological and physiological differences. (…)