Are Dolphins Mammals
While dolphins swim in the water and look more like fish than your typical mammals, they are actually what scientists refer to as "cetaceans" or marine mammals.
Dolphins came into evolutionary play starting during the Eocene Epoch. There is even evidence from the fossil record discovered in Pakistan more than four decades ago that said dolphins likely made the transition to the water from land during that era.
They quickly adapted to the water, however.
Today, we want to dive in and explore the question,
Why are dolphins mammals?
What Are Dolphins?
People often ask,
Are dolphins fish?
The answer to that question is no.
Dolphins are mammals.
Dolphins belong to an animal group known as cetaceans, which includes porpoises and whales, which are other marine animals we consider mammals.
These unique creatures have developed the ability to thrive in oceans around the world, though there are also many that thrive in freshwater systems too.
FUN FACT: Scientists believe that the closest-living dolphin relative is the hippopotamus.
What Makes Dolphins Mammals?
Before we dive in, let's look at some of the definitive characteristics of mammals:
Dolphins Have Lungs
You may have wondered why dolphins like to come up out of the water every so often.
It's actually because, just like humans, they must come up for air.
When bottlenose dolphins breach the surface of the water, they blow away water using their blowholes to take in air.
The water that we see blowing off the top of the dolphin is water from their bodies, not their lungs.
In blowing off this excess water, these marine mammals have the ability to inhale clean air with their blowholes.
The way that dolphins differ from land mammals is that they do not breathe air from their mouths. For this reason, they're able to swallow their prey while underwater while keeping water from entering their lungs. A dolphin's blowhole is the tool it uses to breathe.
Beyond that, dolphins have uniquely collapsible lungs, allowing them to dive deep without becoming victims of decompression sickness. They can also breathe air much quicker than humans can because of these collapsible lungs.
FUN FACT: With each breath, a dolphin is able to exchange around 80% of the air in its lungs.
Dolphins are Warm-Blooded Animals
Warm-blooded mammals are unique in the animal kingdom, as compared to cold-blooded animals, they are able to maintain a higher body temperature. This characteristic is unique to homeothermic animals or warm-blooded animals, including birds and dolphins.
Scientists say that both of these species of animals developed a warm-blooded system so that they could deter fungal infections. If you've ever owned a reptile or amphibian, you know that they often fall victim to fungal infections.
Dolphins Have Hair Follicles
When they are born, dolphins have hair on their rostrum. However, very soon after they are born, this hair falls out.
With that said, if you look closely at adult dolphins, you can still see their hair follicles. Unlike humans, dolphins don't need hair to maintain their body temperature, as they have thick layers of fat called blubber on their bodies.
Because dolphins have hair when they are born, many evolutionary biologists believe they have a deeper connection to other mammals that lived on land millions of years ago.
There are many other marine mammals that live their lives on land and in the water and use their hair to insulate their organs and protect them from cold temperatures. For most marine mammals, however, blubber is the primary insulation source.
River dolphins are quite unique in this regard. If you take a close look at their snouts, you can see small hairs. Researchers believe these hairs are there to act as sensory organs, making up for the fact that they don't have very good eyesight.
Dolphins Do Not Lay Eggs
Unlike fish, reptiles, amphibians, and insects, dolphins give birth to live young instead of laying eggs. Birds do not give birth to live young, so even though they have warm blood, they are not land-dwelling mammals.
A dolphin's sexual maturity depends on its size. Unlike humans, dolphins don't reach sexual maturity by a certain age. When they have reached around 90% of their full-body length, they will also reach sexual maturity.
This sexual maturity can be anywhere from five to twelve years old. A dolphin pregnancy will last somewhere around 12 months. They also get pregnant pretty often, somewhere about two to four years. On average, however, dolphins get pregnant every three years.
Dolphins Produce Milk
All mammals produce milk, and dolphins are no different. What's unique about dolphins is that they have mammary glands that begin producing milk during the gestation period. Essentially, a dolphin that is pregnant has the ability to feed other calves while they are waiting to give birth to live young.
Most dolphins will typically spend around three years nursing. However, there are some dolphins mothers that will spend around five years nursing.
As you may have guessed, the type of milk that dolphins produce is far different from the milk that humans produce. However, it is very similar in its high-fat content to milk produced by rabbits, reindeer, and dogs. The thing that separates dolphin milk from these other animals' milk is that it has a very low lactose content. Dolphin calves also have unique straw-like tongues that they can use to latch onto their mother's nipples to form waterproof seals, allowing them to drink milk when they are beneath the water's surface.
Dolphins Are Social Creatures
While biologists don't consider social behavior a mammalian characteristic, it is worth noting that these creatures engage in extremely intricate social networks. They have incredibly large, complex brains, which is one of the reasons we believe dolphins are considered mammals and not fish.
The bottlenose dolphin, for example, has a unique evolutionary convergence that is very similar to that of primates. They have an acute sense of self-awareness. The only true difference between them and apes is that they've adapted to the aquatic lifestyle.
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