Oh My Dolphin! Learn 10 Exquisite Facts about the Most Intelligent Aquatic Animal

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Updated on: Educator Review By: Michelle Connolly

In a YouTube video posted by BBC Earth and viewed over eight million times, two bottlenose dolphins were swimming peacefully in the large tank of the New York Aquarium. Suddenly they came across a mirror window.

“What is that?” they must have wondered curiously.

On the other side of the window, a researcher from Columbia University was standing, watching in silent amusement what the two cute marine animals were doing.

The two dolphins happily wiggled their flippers. They opened their mouths to look inside them. This made them look as if they were laughing, especially with that joyful sound they made. They also twisted to see the reflection of their bellies.

According to the researcher, dolphins do not display such ‘odd’ behaviours when they meet other individuals. So they must have been aware that what they saw was not but a reflection of themselves. For us, this is super fun to watch. For scientists, it is a sign of intelligence.

This is known as the mirror self-recognition test. Only humans and a few ape species can recognise their reflections. This means they are aware of themselves. Such a level of awareness translates to intelligence, according to scientists.

What we mentioned above was part of a three-year study in which researchers closely studied dolphins. Their fast self-recognition, along with many other traits, got them classified as intelligent creatures, side by side with us, orangutans, and chimpanzees.

Magnificent, is it not?

Well, we are not stopping here. In this article, we are demonstrating 10 unbelievably stunning facts about dolphins that will make you love them even more—we genuinely do not think anyone does not like those cute joyful aquatic animals.

1. Dolphins are not fish but mammals.

Unlike the common belief, not all aquatic animals are fish. Many of them, like dolphins, are mammals. Mammals and fish are so different. For instance, they are warm-blooded, while fish are cold-blooded creatures.

So what exactly does that mean?

Warm-blooded animals have a higher internal body temperature than that of their surroundings. It is also independent of it. So if the external temperature gets low, their bodies produce heat to warm them up. If it is hot, their bodies will cool down. Humans, dolphins, and birds are warm-blooded.

On the other hand, cold-blooded animals cannot regulate their body temperature according to the change in the outer temperature. They rely on their surroundings to stay warm and alive. That is why they cannot live in extremely cold conditions. Insects, reptiles, and fish are cold-blooded animals.

Another difference between both creatures is how they breathe. Dolphins breathe through lungs. So they have to go to the surface periodically to catch a breath using the blowhole found on top of their heads. In fact, they cannot stay underwater for more than 10 minutes. Otherwise, they will suffocate and drown.

On the other hand, fish are accustomed to surviving permanently underwater. They have incredible gills that extract dissolved oxygen from the water. But those gills cannot get oxygen from the air. So when fish go to the surface, they die.

In addition, dolphins give birth to fully-developed live babies, which they carry in their wombs. They also feed them milk until they are able to eat solid food. Alternatively, most fish lay eggs which hatch after a certain period.

2. They descended from a four-legged land mammal.

The evolution of animals is such an incredible process and super fun to learn about. The transformation that organisms undergo over millions of years by small but steady changes shows how miraculous our nature is.

For instance, birds are thought to have evolved from dinosaurs! Likewise, scientists believe that dolphins descended from a four-legged land walking ancestor around 49 million years ago.

At some point in history, this ancestor decided to wet its legs in the water. Captivated by the experience, it decided to go for a swim. Then it must have tried diving. Generation after generation, this animal started to experience some physical changes to adapt to its new aquatic environment.

Over millions of years, the front legs turned into flippers while the back legs gradually disappeared. The tail became a fin, and the nostrils moved toward the top of the head. Those, besides many other changes, resulted in the dolphin we are now familiar with.

Dolphins became fully aquatic, meaning they now live permanently in water, around five million years ago.

3. There are 40 species of dolphins.

As you hopefully remember, the taxonomy hierarchy is used to classify extant and extinct organisms. The most specific class is the species. Every species is unique, no matter how much in common it may have with other species.

Unlike the common belief, there is not just one type of dolphin but many. In total, there are 40 extant species of them. Because they differ widely in size, skin colour, habitat, body shape and, well, how long their noses are, scientists classified those 40 dolphin species into five families—we will get to them in a bit.

Generally speaking, most dolphins live in every water around the world except for the Arctic Ocean and Antarctica. But typically, they prefer warmer temperatures and are more abundant in tropical and temperate waters.

Dolphins look like they have the same cigar-like body shape but with different measurements. For instance, the smallest (and rarest) species measures 1.2-1.6 metres and weighs around 50 kg on average. On the flip side, the largest species has a total body length of 9.5 metres and a maximum weight of 11 metric tons!

Speaking of colours, dolphins display a wide range of them. They can be as light as white, pink, pearl or light brown or as dark as grey, blue and even black. Every type has the belly and underparts of a lighter colour than that of the head and back. Some species have stripes, and others have spots.

In many species, there is not much of a difference between male and female individuals. Some species have one sex larger than the other. Other species have males and females utterly different in colour and size.

4. The killer whale is actually a dolphin.

We have seen before how confusing naming animals is. Sometimes, animals are given names that have nothing to do with their classification. For instance, the extinct Tasmanian tiger was not a tiger. It looked like a dog and a red fox, but it was neither a dog nor a fox.

This is the case with some dolphin species, which are referred to as whales for some reason. The super-duper killer whale is, in fact, a dolphin.

Also referred to as the orca, the killer whale is the largest dolphin species. It can reach a body length of 9.5 metres and a maximum weight of around 11 tons, with females typically being a little smaller than males.

This large ‘whale’ is characterised by its dazzling colours. The head and back, including the dorsal fin, flippers, and tail fin, are black, while the underparts are white. The killer whale also has a few oval-shaped white spots on its black back.

Like sharks and polar bears, the killer whale is an apex predator. It feeds on other animals, usually marine ones, but no other animal feeds on it. In that context, the killer whale generally eats a large variety of fish, but it also likes to hunt seals.

Unlike most other species, orcas survive in cold water. So a large population is found in the coastal waters of Norway and Alaska in the north and Antarctica in the south. There is also another large population roaming the eastern North Pacific Ocean, between the east coast of Russia and the west coast of the US.

5. Dolphins live in saltwater and freshwater.

Not all 40 extant dolphin species live in saltwater. Well, the majority of them do, but the rest live in freshwater.

A few paragraphs ago, we mentioned that all extant species of dolphins are divided into five families. Remember that? Well, these families are mainly characterised by the habitat in terms of how salty the water is!

Around 35 species are oceanic. They belong to the family Delphinidae, and yes, they live in saltwater. The Indian river dolphins is a freshwater family that includes two species only.

Likewise, the river dolphins are three freshwater species living in the rivers of South America. One of them is the La Plata dolphin, which lives in brackish water. Brackish water is saltier than freshwater but less salty than saltwater. In other words, this La Plata can survive both in the sea and the river.

So in total, there are 35 saltwater dolphins and five freshwater ones. Indeed, there are a few differences between the two groups thanks to the difference in their environments. 

For instance, oceanic dolphins enjoy better vision and larger eyes than the river species. That is because sea water is way more clear than muddy river water. The mud in the freshwater, unfortunately, causes the eyesight of the freshwater dolphins to deteriorate the older they get.

Another difference is the snout length. Oceanic dolphins live in a vast environment, so they depend more on echolocation than their snouts to find food—we will explain what this is in a few paragraphs. So their snouts are not that long.

On the other hand, rivers are way narrower and shallower than oceans. So freshwater dolphins have longer snouts than their oceanic counterpars to help them find food, which can be pretty nearby. 

Speaking of food, oceanic dolphins eat different kinds of fish than the freshwater ones.

6. They are highly sociable animals.

Like monkeys, dolphins are very sociable. They usually live in groups called pods. Pod size differs according to the species, habitat, and food availability. But generally speaking, a pod can be anywhere between two and 40 individuals. Sometimes, female dolphins and their calves form what is known as nursing groups.

Members of the same pod are extremely bonded to one another. They show cooperation and care for one another, especially the elderly and the ill. They forage, play, travel, and sleep together. When food is abundant, pods sometimes get together to form superpods with several hundred individuals.  

That said, dolphins also show aggressive behaviours. This is very common among male individuals fighting to win the heart of a female. Whoever wins the fight gets to marry the princess. Sometimes, the loser is sent into exile!

7. They are super intelligent.

Unlike what many may think, brain size does not necessarily indicate intelligence. Even if some species with large brains are intelligent, such as us and chimpanzees, that does not necessarily imply that species with larger brains are more intelligent.

Scientists use other measurements to see how intelligent these mammals are. The most important one of these is watching their behaviours in different situations. A famous test is the one we mentioned earlier, the mirror test. As the dolphins could recognise themselves in the mirror, they are most probably intelligent.

Another indicator is how dolphins use tools to perform specific tasks. Female bottlenose dolphins were seen to tear sponges and use them to cover their snouts while looking for food. This way, they protect them from fish bites or any other possible injuries. 

Interestingly, female bottlenose dolphins are the only individuals who do that. Males do not. The females even pass this learned behaviour on to their daughters (but not to their sons, and only God knows why!) This ‘teaching/learning behaviour’ is a sign of intelligence.

It is also how dolphins react to different things that shows intelligence. Scientists found that they have the same brain cells as us, which we use to socialise and express emotions. So they deduced that dolphins must be able to display emotions too.

8. They have two stomachs.

Dolphins are diurnal animals. They forage during daylight and rest at night. They feed on a wide range of fish, squid, shrimp, and prawns. As we mentioned, the orca sometimes hunts seals.

Interestingly, dolphins have two stomachs. They use one of them to digest the food and get energy to look for more food. The other one is used to store food. This provides backup energy if the dolphins ever feel hungry during the night.

9. They use echolocation.

Although marine dolphins have good eyesight, this sense is backed by another great feature, echolocation, that enables them to ‘see’ more clearly, especially from a distance.

Like bats, dolphins produce high-frequency sound waves to explore the surrounding area. These waves travel in the water much faster than in the air. When they hit an object, they are reflected to the dolphins as an echo.

The dolphins’ lower jaws work just like antennas. They pick up the echo, move the information to the ear and then to the brain to decipher it. 

Surprisingly, this echo tells the dolphins many things about that object the sound waves hit. They can easily identify how far and big the object is. They also learn if the object is moving (and how fast it is) or stationary.

10. They sleep vertically.

Because they have lungs, dolphins often need to get to the surface to breathe. Sometimes they can hold their breath underwater but only for a few minutes. Here one cannot help but wonder, what about sleep, then? If they typically sleep eight hours a day, how do they manage to breathe?

Well, dolphins sleep in one of two ways: resting in the water, without moving, either horizontally or, yes, vertically. They can also sleep by swimming slowly while staying near the surface.

Dolphins fall asleep in a vertical position while keeping their blowholes above the water. Interestingly, they sleep with one half of the brain active and the other inactive. So they stay partially awake.

This little consciousness keeps the dolphins breathing and helps them remain alert to any dangers or predators, mainly sharks.

Both brain halves take turns staying up for the night watch. So each one of them gets around four hours of sleep. This way, dolphins sleep without drowning. 


Here we get to the end of today’s journey, where we learned some uncommon and hopefully interesting facts about the most intelligent and charming aquatic animal, the dolphin.

In this article, we demonstrated the difference between dolphins as mammals and fish. We looked into their evolution over millions of years and how they turned from a land-dwelling animal to fully aquatic creatures. We also studied the classification of dolphins into families based on their habitat.

After that, we explored some fantastic traits dolphins enjoy, from sociability and intelligence to how they use echolocation and why they sleep in a vertical position.

We hope you found today’s article useful as much as we loved writing it for you. You can learn about the Pacific Ocean, where many dolphin species live here. You can also learn about many, many other things by visiting the different pages of our website.

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