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.
Paleontologists and comparative anatomists have made important contributions to knowledge about the evolution of many animals. Zoologists who study embryology deal with the formation and development of organisms from fertilized eggs to birth. Physiology is the study of the functions of animals. Physiologists may observe how the heart pumps blood, how nerves transmit impulses, and how muscles contract. Other areas of zoology include genetics and ecology.