This interactive module explores the circulatory systems of major vertebrate groups to gain insights into their evolution.

Over millions of years of vertebrate evolution, the heart has changed dramatically from a relatively simple two-chambered heart in fish, to a three-chambered heart in amphibians and reptiles, and to a four-chambered heart in mammals and birds. This Click & Learn allows students to compare the circulatory systems of eight different vertebrates, including their heart structure and function.

Students can also visualize interesting adaptations such as the crocodile’s ability to change its circulatory pattern when diving underwater. The heart of a mammalian fetus shows a similar circulatory pattern.