Inferences from allometry and fossils: dwarfing of elephants on islands
Introduces the "island rule' for mammalian body size: the tendency of small mammals to enlarge and carnivores and ungulates to dwarf. For large mammals, resource limitation favours smaller body size; the genetic background to this is reviewed. Occurrence of dwarfed elephants is discussed, with comments on modern analogues, but attention focuses on Pleistocene insular forms. Inferences are drawn regarding body mass and life history (including dietary selectivity), and shape is examined as evidence for mechanical function and heterochronic evolution. Selection for maturity at small size is likely to have been a primary characteristic, since 1) body sizes among insular forms of elephants are consistently small but morphologies are diverse; 2) livestock breeding suggests that mature body size is more responsive to selection than are many other features of growth or morphology; and 3) calculations show the pronounced reduction in food required by dwarfs compared to normal-sized animals. -P.J.Jarvis
