The subdivision of the science of biogeography that is concerned with the detailed description of the distribution of animals and how their past distribution has produced present-day patterns. Scientists in this field attempt to formulate theories that explain the present distributions as elucidated by geography, physiography, climate, ecological correlates (especially vegetation), geological history, the canons of evolutionary theory, and an understanding of the evolutionary relationships of the particular animals under study.

The field of zoogeography is based upon five observations and two conclusions. The observations are as follows. (1) Each species and higher group of animals has a discrete nonrandom distribution in space and time (for example, the gorilla occurs only in two forest areas in Africa). (2) Different geographical regions have an assemblage of distinctive animals that coexist (for example, the fauna of Africa south of the Sahara with its monkeys, pigs, and antelopes is totally different from the fauna of Australia with its platypuses, kangaroos, and wombats). (3) These differences (and similarities) cannot be explained by the amount of distance between the regions or by the area of the region alone [for example, the fauna of Europe and eastern Asia is strikingly similar although separated by 6900 mi (11,500 km) of land, while the faunas of Borneo and New Guinea are extremely different although separated by a tenth of that distance across land and water]. (4) Faunas strikingly different from those found today previously occurred in all geographical regions (for example, dinosaurs existed over much of the world in the Cretaceous). (5) Faunas resembling those found today or their antecedents previously occurred, sometimes at sites far distant from their current range (for example, the subtropical-warm temperate fauna of Eocene Wyoming, including many fresh-water fishes, salamander, and turtle groups, is now restricted to the southeastern United States).

The conclusions are as follows. (1) There are recognizible recurrent patterns of animal distribution. (2) These patterns represent faunas composed of species and higher groups that have evolved through time in association with one another.

Two rather different approaches have dominated the study of zoogeography since the beginning of the nineteenth century: ecological and historical. Ecological zoogeography attempts to explain current distribution patterns principally in terms of the ecological requirements of animals, with particular emphasis on environmental parameters, physiological tolerances, ecological roles, and adaptations. The space and time scales in this approach are narrow, and emphasis is upon the statics and dynamics of current or very recent events. Historical zoogeography recognizes that each major geographical area has a different assemblage of species, that certain systematic groups of organisms tend to cluster geographically, and that the interaction of geography, climate, and evolutionary processes over a long time span is responsible for the patterns or general tracks. Emphasis in this approach is upon the statics and dynamics of major geographical and geological events ranging across vast areas and substantial time intervals of up to millions of years. The approach is based on concordant evolutionary association of diverse groups through time.Ecology