Marine Mammals at the Zoo

Although technically not inside the Oceans exhibit, the Indianapolis Zoo's marine mammals share one thing in common with their fishy cousins - a watery environment. The Zoo marine mammal collection includes Atlantic bottlenose dolphins (which star in their own exhibit, the Dolphin Adventure, Pacific walrus, polar bear, California sea lions, harbor seals and gray seals. The seal and sea lion exhibit is near the entrance to Oceans, while the polar bear exhibit is positioned just outside the exit from Oceans. The walrus exhibit, including an underwater viewing theater, is a bit farther on and leads directly to the Dolphin Adventure Pavilion.  Photo by Ellen Jackson

Marine mammals are a diverse group of roughly 120 species of mammals that are primarily ocean-dwelling or depend on the ocean for food. They include the cetaceans (whales, dolphins, and porpoises), the sirenians (manatees and dugong), the pinnipeds (true seals, eared seals and walrus), and several otters (the sea otter and marine otter). The polar bear is also usually grouped with the marine mammals.

Marine mammals evolved from land dwelling ancestors and share several adaptive features for life at sea such as generally large size, hydrodynamic body shapes, modified appendages and various thermoregulatory adaptations. Different species are, however, adapted to marine life to varying degrees. The most fully adapted are the cetaceans and the sirenians, whose entire life cycle takes place under water, whereas the other groups spend at least some time on land. Photo by Rick Lang

Many marine mammal populations are vulnerable or endangered due to a history of commercial exploitation for blubber, meat, ivory and fur. Most species are currently protected from commercial exploitation. The effects of climate change are also threatening the sea ice home of the polar bear.

Since mammals originally evolved on land, their spines are optimized for running, allowing for up-and-down but only little sideways motion. Therefore, marine mammals typically swim by moving their spine up and down. By contrast, fish normally swim by moving their spine sideways. For this reason, fish mostly have vertical caudal (tail) fins, while marine mammals have horizontal caudal fins.