Data from: The evolution of mammal body sizes: responses to Cenozoic climate change in North American mammals

Explanations for the evolution of body size in mammals have remained
surprisingly elusive despite the central importance of body size in
evolutionary biology. Here, we present a model which argues that the body
sizes of Nearctic mammals were moulded by Cenozoic climate and vegetation
changes. Following the early Eocene Climate Optimum, forests retreated and
gave way to open woodland and savannah landscapes, followed later by
grasslands. Many herbivores that radiated in these new landscapes
underwent a switch from browsing to grazing associated with increased
unguligrade cursoriality and body size, the latter driven by the
energetics and constraints of cellulose digestion (fermentation).
Carnivores also increased in size and digitigrade, cursorial capacity to
occupy a size distribution allowing the capture of prey of the widest
range of body sizes. With the emergence of larger, faster carnivores,
plantigrade mammals were constrained from evolving to large body sizes and
most remained smaller than 1 kg throughout the middle Cenozoic. We find no
consistent support for either Cope's Rule or Bergmann's Rule in
plantigrade mammals, the largest locomotor guild (n = 1186, 59% of species
in the database). Some cold-specialist plantigrade mammals, such as
beavers and marmots, showed dramatic increases in body mass following the
Miocene Climate Optimum which may, however, be partially explained by
Bergmann's rule. This study reemphasizes the necessity of considering
the evolutionary history and resultant form and function of mammalian
morphotypes when attempting to understand contemporary mammalian body size
distributions.