Are Dolphins Mammals? – Everything You Need to Know!

Group of mammal dolphins swimming in the ocean

Dolphins are amazing creatures that live in the water, and they are known for their intelligence and playful behavior. But have you ever wondered what kind of animal a dolphin is? Are dolphins mammals?

Yes, dolphins are mammals. They breathe air, give birth to live young, and nurse their offspring with milk. They are part of the Cetacea order, including whales and porpoises. Moreover, unlike fish, dolphins have lungs instead of gills.

In this article, we will explore the reasons why dolphins are considered mammals and not fish. Let’s dive in and learn more about dolphins!

What Makes Dolphins Mammals?

Two dolphins jump with the waves

Despite living in the water, dolphins possess key characteristics that classify them as mammals. 

While their marine environment might suggest otherwise, they have many features in common with land mammals. Let’s explore the traits that firmly classify dolphins as mammals.

1. Dolphins breathe using blowholes

Unlike fish that extract oxygen from water using gills, dolphins breathe air. They have a specialized structure called a blowhole on the top of their heads. 

This blowhole acts as their nostril and allows them to inhale and exhale. When a dolphin surfaces, it forcefully expels air through the blowhole, often seen as a spout of water vapor. 

The design of the blowhole ensures that water doesn’t enter their lungs. This breathing method clearly indicates their mammalian nature, as it’s similar to how land mammals breathe using lungs.

Here’s a brief scientific explanation of how dolphins use their blowholes to breathe:

The physics of dolphin blowholes | Science News

2. Dolphins birth and nurse live young

One of the defining characteristics of mammals is giving birth to live offspring. Dolphins are no exception. 

They do not lay eggs like many marine creatures. Instead, a mother dolphin gives birth to a live calf after gestation. Once born, the calf is immediately brought to the surface by the mother for its first breath. 

Furthermore, mother dolphins produce milk and nurse their young, providing them with the essential nutrients they need to grow and thrive. 

While a handful of aquatic creatures like whales and manatees nurse their young with milk, most aquatic animals do not exhibit this behavior. 

Instead, many aquatic species lay eggs or release larvae, which then fend for themselves without any direct nourishment from the parent.

Watch this video to see how a dolphin teaches its calf how to fend for itself:

Dolphin Parenting | National Geographic

3. Hair follicles are present around their blowhole

While dolphins might appear smooth and hairless, they have hair follicles, especially around their blowhole. These follicles are remnants of their mammalian ancestry. 

Most mammals have hair or fur, and while dolphins have lost most of theirs through evolution, the presence of these follicles is a clear sign of their mammalian lineage. 

These tiny hairs also play a role in sensory perception. Dolphins use them as tiny sensors to navigate the underwater world.

On a related note, dolphins evolved from terrestrial animals that are related to modern-day hippos. These ancestors, from the order Artiodactyla, transitioned to aquatic life over millions of years. 

I became particularly interested in this topic when I learned about the Pakicetus fossil, an early cetacean from Pakistan. Its discovery provides evidence for the theory behind the dolphin’s evolution. 

Such evolutionary ties give insight into the dolphin’s unique features, such as their hairy blowholes and other mammalian traits.

4. Dolphins regulate their body temperature 

Dolphins, like all mammals, are warm-blooded. This means they can maintain a stable internal body temperature regardless of the external environment. 

Even in cold waters, dolphins can keep their bodies warm. They achieve this by combining their metabolic processes and their insulating layer of blubber.

This ability to regulate body temperature is a telltale sign that an animal is a mammal. It also sets them apart from cold-blooded creatures like fish.

5. They have insulating blubber under their skin 

Beneath their skin, dolphins have a thick layer of blubber. This blubber serves multiple purposes. It acts as an insulator, keeping the dolphin warm in colder waters. 

Additionally, it provides buoyancy and stores energy in the form of fat. This adaptation is crucial for their marine life, as it allows them to thrive in various water temperatures and conditions. 

Many marine mammals, not just dolphins, possess this blubber layer for the same reasons. Similarly, other animals carry a similar fat reserve for the same purpose.

However, the term “blubber” is commonly reserved for marine mammals to describe their insulating layer of fat.

6. Dolphins possess a large and complex brain

Dolphins are renowned for their intelligence. This is largely due to their sizable and intricate brains. Their brain-to-body ratio is among the highest in the animal kingdom. 

According to an article by the National Science Foundation, scientists have discovered that dolphins’ brains are four to five times larger than expected for their body size. Meanwhile, humans’ brains are seven times larger. 

The study suggests that primates and big sea animals like dolphins developed their large brains in different ways as they evolved, but both ended up being equally smart.

This complex brain allows them to exhibit advanced behaviors, from problem-solving to social interactions. This also explains how dolphins can communicate, form social networks, and even use tools in some instances. 

In essence, while the large brain and advanced behaviors of dolphins are not exclusive proof of their mammalian status, they are indicative of it, especially when viewed in the context of other marine animals.

How Are Dolphins Different From Fish?

Dolphins swimming with a school of fish

Even though dolphins live in water, they are quite different from fish. They have unique features that make them stand out from other sea creatures like fish.

Here are some ways dolphins are different from fish: 

  • Dolphins are warm-blooded, while most fish are cold-blooded.
  • Dolphins breathe through their lungs, whereas fish use gills.
  • Dolphins have a streamlined body with a dorsal fin, while fish have scales covering their bodies.
  • Dolphins give birth to live young, while many fish lay eggs.

While dolphins and fish inhabit the same aquatic environments, their distinct biological and physiological traits set them apart.

Why Do Dolphins Live in Water If They Are Mammals?

Dolphins, along with their close relatives whales and manatees, are part of a subset of mammals that have adapted to an aquatic lifestyle. Their evolutionary lineage traces back to terrestrial ancestors. 

Over time, as they evolved, the ancestors of dolphins, who once lived on land, changed in shape and function to survive better in water.

Dolphins have changed in ways, like having streamlined bodies to swim easily, developing a blowhole to breathe while staying on the water’s surface, and altering the shapes of their limbs.

While they have become specialized for life in the water, dolphins retain key mammalian traits, such as lung-based breathing, live births, and mammary glands for nursing their young. 

Common Misconceptions About Dolphins

Dolphins swimming in the sea

Dolphins have always fascinated us with their playful nature and graceful movements. However, several misconceptions about these marine mammals often lead to confusion. 

Let’s address some of the dolphin myths and set the record straight:

  • Myth 1: Dolphins are fish. A common belief is that dolphins are fish because of their aquatic habitat. In reality, dolphins are marine mammals, not fish.
  • Myth 2: Dolphins and sharks are related. While dolphins and sharks may share a similar habitat and even body shape, they are fundamentally different. Dolphins are mammals, whereas sharks are fish.
  • Myth 3: Dolphins can breathe underwater. Unlike fish that have gills, dolphins need to surface regularly to breathe. They inhale air through their blowholes located on top of their heads.
  • Myth 4: All dolphins live in the ocean. It’s a misconception that all dolphins are ocean dwellers. While many live in the ocean, some dolphin species inhabit freshwater rivers.
  • Myth 5: Dolphins are always friendly and harmless. Dolphins are often portrayed as friendly creatures, and while many are, it’s important to know that they can still exhibit aggressive behaviors when threatened or provoked.
  • Myth 6: Dolphins evolved from hippos or other large land mammals. While dolphins share a common evolutionary ancestor with even-toed ungulates, they did not directly evolve from hippos. This is a common misconception for some.
  • Myth 7: All dolphins look and behave the same. With 49 recognized species of dolphins, it’s clear that they come in various shapes, sizes, and behaviors. Each species has its unique characteristics and ways of interacting with its environment.

Dolphins frequently appear in tales, but it’s still important to distinguish myth from fact. Recognizing the truth about dolphins enhances our appreciation of these sea creatures. 

Frequently Asked Questions

Two dolphins playing during sunset

Why Is a Dolphin a Mammal and Not a Shark?

Sharks are fish, and dolphins are mammals. The big difference is how they breathe and reproduce. 

Dolphins use their lungs to breathe and need to come up to the surface for air. They also give birth to live babies and feed them with milk. Sharks, on the other hand, breathe through gills, and most lay eggs.

Do Dolphins Produce Milk?

Yes, they do. Just like other mammals, female dolphins have special glands that make milk. This milk is what they use to feed their babies.

Do Dolphins Give Birth to Live Young?

Dolphins don’t lay eggs. Instead, they give birth to live babies, known as calves. After being born, a dolphin calf stays close to its mom, relying on her for food and safety.

Final Thoughts

Dolphins are good indicators of the health of the ocean. Their well-being often reflects the overall state of our marine environments. Needless to say, learning about them is always worthwhile.

As we’ve explored, dolphins are undeniably mammals. With their intelligence, social behaviors, and body structures, these agile and elegant swimmers connect the gap between the land and aquatic worlds.

Hopefully, this guide has captured your interest in the world of marine mammals, especially dolphins. If you have any thoughts or questions about dolphins, leave a comment below!

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