The existence of distinctly different forms of males and females. For example, sexual dimorphism is very obvious in newts of the genus Triturus, which develop even more exaggerated secondary characteristics during the breeding season.
Refers to the case where males and females of a species look different. For example, male fence lizards have blue bellies and throats, while females do not; male birds are often more colorful than female birds.
refers to the difference in size between one sex and another in a given species. In some species males are larger (i.e. elephants), in others females are (i.e hyenas) and in some they are about the same size (i.e. geese)
The differences in size, structure, or appearance exhibited between the males and females of some species. The Purple Martin exhibits sexual dimorphism because males and females each possess different colors and markings during the breeding season.
"The development of physical and other differences between the sexes of the same species, especially when this difference extends beyond the reproductive organs to overall size, color, and the development of special features." ("Encyclopedia of Marine Mammals," William F. Perrin, Bernd Wursig and J.G.M. Thewissen, Academic Press, 2002, p. 1367.)
The state of affairs, observed in many species, in which the sexes differ in form (such as deer antlers or peacock tail feathers) or size. Sexual dimorphism is minimal among monogamous animals and maximal among polygamous ones.