By Sara Thompson
Special to the Enterprise
Our oceans and waterways are teeming with all kinds of life. From fish, to cephalopods, gastropods, bivalves, and more! Even mammals have found a way to live in the water full time as well. All mammals are identified by being warm-blooded, breathing air through lungs, having hair or fur for some of their lives, giving birth to live young, and producing milk to nourish their babies. Marine mammals can be categorized into four different groups: cetaceans, pinnipeds, sirenians, and marine fissipeds. All of these types of marine mammals have a variety of adaptations that allow them to live aquatic life.
Cetaceans are the group that makes up whales, porpoises, and dolphins. This group has adapted to living full time in the water by losing their hind legs, developing a tail with flukes, and their forelimbs have evolved into flippers. Their bodies are also ‘torpedo’ shaped for better movement through the water, and a dorsal fin for balance. They use specialized blood flow for regulating their temperature and have organs and blood vessels that specialize in better oxygen storage. They still breathe air when they surface, using a blowhole at the top of their heads to get oxygen to their lungs. Cetaceans are born with small hairs on their bodies and small whiskers on their snout. They quickly lose these hairs and use thickened skin and layer of blubber to help with regulating their temperature. Female cetaceans do nurse their young until they are old enough to eat larger prey, such as fish, with the rest of their family groups.
Pinnipeds are the group that makes up seals, sea lions, and walruses. These marine mammals spend some of their time in water and some on land, but also have specialized adaptations to help them live in and around the water. Pinnipeds have a set of fore-flippers and hind-flippers that allow them to move both on land and in water. Their body shape also helps with moving through both water and on land. Their bodies are covered in long, fine hairs that help trap heat to their skin, which is also thick layer of blubber underneath to keep their core warm. Their blood is also adapted to carry higher concentrations of oxygen and can fully exhale air from their lungs and partially collapse them for deep dives.
Sirenians are manatees and dugongs. They are the only herbivorous marine mammal, feeding primarily on sea grasses and other marine plants, but do occasionally eat small invertebrates living in these plants. Like cetaceans, they also live fully in the water, having an adapted body to allow them to swim and dive for extended periods. They have large whiskers on their snouts that help with moving sand around in search of food.
Marine fissipeds also spend part of their time on land. This group includes polar bears and sea otters. They are included because they primarily hunt in the water and have a variety of adaptations to aid a partially aquatic life. They have thick, water-proof hair and a layer of thick fat for staying warm.
All these animals still hold the characteristics of mammals, but all have their own facinating adaptations to better live in an aquatic environment.
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