Extinct horses to scale illustrating differences in size: Left to right: Mesohippus , Neohipparion , Eohippus , Equus scotti and Hypohippus . (Heinrich Harder, 1914; Public Domain) The evolution of body size has been the focus of countless studies, not only in palaeontology but also in evolutionary biology using data from extant animals (or neontology as palaeontologists would say). While some colleagues have argued recently that body size is not necessarily a good trait to study, nonetheless, it still stands that body size is an important factor of fundamental biological phenomena, including metabolism, physiology, biomechanics, and ecology. For instance, the largest source of variance in biomechanical performance measures like bite force is body size - a lion's bite force is an order or two higher in magnitude than that of a domestic cat just purely out of simple scaling. Similarly, prey size categories, such as large, medium/mixed and small, are highly affected by p...