  The group of large aquatic mammals has representatives being the largest
living beings on earth, surpassing the weight and size of dinosaurs. In this
paper, we present some empirical evidence and a mathematical model to argue
that fat accumulation in marine mammals triggers a series of metabolic events
that result in these animals' increased size. Our study starts by analysing 43
ontogenetic trajectories of species of different types and sizes. For instance,
the analyses include organisms with asymptotic mass from 27g (Taiwan field
mouse) to $2.10^{7}$g (grey whale). The available data allows us to determine
all available species' ontogenetic parameters (catabolism and anabolism
constant, scaling exponent and asymptotic mass). The analyses of those data
show a minimisation of catabolism and scaling exponent in marine mammals
compared to other species analysed. We present a possible explanation for this,
arguing that the large proportion of adipose tissue in these animals can cause
this minimisation. That is because adipocytes have different scaling properties
in comparison to non-adipose (typical) cells, expressed in reduced energetic
demand and lower metabolism. The conclusion is that when we have an animal with
a relatively large amount of adipose tissue, as is the case of aquatic mammals,
the cellular metabolic rate decreases compared to other animals with the same
mass but with proportionally smaller fat tissue. A final consequence of this
cause-effect process is the increase of the asymptotic mass of these mammals.
