AbstractMarine mammals include toothed and baleen whales, as well as seals, sea lions, sea cows, sea otters and polar bears. They are adapted to an aquatic life in oceanic, coastal and riverine habitats. They range in size from sea otters to blue whales. The extreme diversity of marine mammals is related to their adaptations to different habitats and their use of different feeding strategies. The different kinds of marine mammals are not closely related but evolved from different terrestrial ancestors. Because they have been exposed to similar environmental constraints in their aquatic way of life, many evolutionary convergences can be found in different lineages. They have torpedo-shaped bodies, thick fur or fat layers to preserve heat, as well as impressive diving abilities. Here, we discuss these adaptations in their physiology and anatomy. Through hands-on exercises, students can test how their own muscle strength and heartbeat are affected by cold water.