Many people assume that Dolphins are fish as they swim gracefully through the water, however, they are not fish. Dolphins are actually mammals. Other famous marine mammals include whales, seals, and manatees. The characteristics that make dolphins mammals are as follows:
- breathe through lungs, not gills
- give birth to live young
- produce milk for their young
- have body hair (doesn’t look like it, but they do!)
Warm-blooded means that their body is able to regulate its own temperature, so they stay warm even when the water temperatures around them are cold. Some of their native environments, such as the waters of the northern Pacific Ocean, can get very chilly. In these places, being warm-blooded is a big advantage for survival. Being warm-blooded also makes dolphins and other cetaceans less prone to infections and other health conditions that affect cold-blooded species.
Lungs, Not Gills
Another central feature of marine mammals is that they have lungs, not gills. Dolphins, like whales, need to periodically come to the surface to replenish their air supply. They have blowholes that they close while diving, and then open at the surface for air.
Marine mammals have also adapted in some special ways to thrive in an aquatic environment. For instance, dolphins exchange 80% of the air in their lungs with each breath, while humans are only capable of exchanging 17%. Marine mammals also have a greater capacity for oxygen storage in their lungs, blood, and muscles. All of this creates a more efficient use of the oxygen in their bodies and is what allows many species to dive for extended periods of time.
Dolphins give birth to live young and do not lay eggs. They can get pregnant on average every two to four years once they’re mature, although some species can have 5-7 years between births. Dolphin calves tend to stay close to their mothers for a few years before venturing off on their own. However, some calves will stay with their mothers for a lifetime.
Along with gestating their young, dolphins produce milk to nourish them. It may seem tricky for calves to nurse underwater, but dolphins have adapted some special physiological traits to work around this issue.
Did you know that dolphins start life with body hair? Newborn calves have hairs on their rostrum (their beak) that fall out soon after birth This is believed to be an evolutionary remnant from when they lived on land.