Figure 1.
Terrestrial and fully aquatic mammal species mass distributions.
Both show the canonical asymmetric pattern: the median size is flanked by a short left-tail down to a minimum viable size and a long right-tail out to a few extremely large species.
Figure 2.
Characteristic species size pattern and cladogenetic diffusion model.
(A) The characteristic distribution of species body sizes, observed in most major animal groups. Macroevolutionary tradeoffs between short-term selective advantages and long-term extinction risks, constrained by a minimum viable size , produce the distribution’s long right-tail. (B) Schematic illustrating the cladogenetic diffusion model of species body-size evolution: a descendant species’ mass is related to its ancestor’s size M by a random multiplicative factor
. Species become extinct with a probability that grows slowly with M.
Figure 3.
Comparison of data and model predictions.
(A) Ex ante predicted cetacean sizes, from a cladogenetic model fitted to terrestrial mammals but with a pelagic (see text), and empirical sizes of 77 extant cetacean species, as complementary cumulative distributions and as (B) smoothed probability densities.