For example, entomology is the study of insects, the largest group of animals. Mammalogy deals with those animals that have hair and that feed their babies on the mother's milk. Ichthyology is the study of fish. A zoologist in any of these fields might spend an entire lifetime studying a single species of animal. Other areas of zoology deal with certain characteristics that many animals have in common.
Taxonomy is the study of naming and classifying animals.
As part of their work, taxonomists establish relationships among different animal groups. For instance, they have shown that bats are more closely related to mice and other mammals than they are to birds. Comparative anatomy is the study of differences and similarities in the body structures of different animals. A comparative anatomist might compare the circulatory systems of sharks, frogs, and cats. Paleontology is the study of prehistoric organisms.