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The answer is in its name, right? Killer whale? You may be surprised to know that orcas are actually more closely related to…dolphins! Weird, huh? Here, we will delve into the taxonomy of these majestic marine mammals, and learn a little bit more about why they are classified as dolphins and not whales.
Why is an orca a dolphin and not a whale?
The appearance of an orca is commonly known, and it’s safe to say that they are very similar to whales. But taxonomically, they are more similar to dolphins. But, why is that the case?
Picture this: a HUGE family tree of all the animals that live on our planet. Each branch shows how closely related they are to one another, based on their genes and traits. Because of their similarities, all dolphins, whales and porpoises are grouped together on a branch known as cetacea. Cetacea then branches off into two smaller groups: “toothed whales” which include species that have teeth in all different shapes and sizes, and “baleen whales” which are species that lack teeth entirely. It is the orca’s 10 cm (4 inch) long teeth that classify them as toothed whales. You might be thinking: so orcas are whales after all? Kind of, but not quite.
Let’s go back to the family tree again. The dolphin family Delphinidae, is one of five families that make up the toothed whales. This is actually where we find the orca, as part of the dolphin family. So yes, they are categorised as toothed whales but it is the placement of their specific family that makes them more closely related to dolphins. So, when someone says that orcas are whales they’re not technically wrong. They just haven’t classified them specifically!
Why have orcas been named “killer whales” if they aren’t technically whales?
Despite being a dolphin, the orca is commonly known as a “killer whale.” This is probably the reason why so many people think it actually is a whale! But where did this name come from? It is believed that the orca was named “whale killer” or “killer of whales” by ancient sailors, when they saw the orca hunting and preying on different whale species. Even the scientific name of killer whales, Orcinus orca, refers to this feeding behavior, as Orcinus translates to “of the realm of the dead” and orca to a type of whale. Over time, the name was morphed into the misleading name that we use today. Even though orcas are apex predators of the oceans, they are not the vicious killing machines that their name makes them out to be!
Why are orcas part of the dolphin family, anyway?
Orcas can grow up to 10 m (32.8 ft) in length, making them the biggest species in the dolphin family. So, wouldn’t their big size classify them with whales? Well, even though they are bigger, orcas are physically more like dolphins than you might think. Their body shapes are similar, allowing them to swim fast and hunt quick prey in the water. Their heads are rounded and narrow into a beak, just like other dolphins! But the one characteristic that really makes them dolphins is their use of echolocation. Dolphins are the only marine mammal that uses echolocation for hunting and navigation. And – you guessed it – this includes the orca!
Echolocation allows dolphins to see their surroundings and can even help them to detect prey and predators. How does it work? Dolphins have a melon on their heads, which sounds silly, but it’s not the type of melon you’re thinking of! This melon is actually made of body fat, and it helps them to make sounds, and to receive the echoes when those sounds bounce back to them. It is also believed that these sounds are used to confuse prey, making it easier for the dolphins to hunt. Orcas use echolocation by sending out click sounds known as a “click train.” The click train can help them find prey at a distance of 152.4 m (500 ft)!
Do orcas act like dolphins?
Short answer: yes! Not only do orcas share similar physical features with other dolphins, but they even behave like them too! Orcas, like dolphins, display unihemispheric sleep, where they shut down one half of the brain and sleep with one eye open. This is to prevent them from drowning, as they still need to breathe oxygen from the surface. Dolphins control which side of their brain sleeps, and can swap sides periodically to get all the sleep they need.
Like other dolphins, orcas are very social animals that live in tightly knit family groups known as pods. These pods can have up to 50 members! The most common type of pods are matrilines, which consist of mothers and their calves. Male orcas can stay with their mothers for their entire lives, while female orcas can leave their mothers for longer periods of time to have calves of their own. Orcas are found all over the world, and each pod has its own dialect and its own way of communicating, just like humans! The members of each pod cooperate when hunting prey, and different pods around the world have even developed different ways of capturing prey. Pods are important because they are the structure through which knowledge is passed down to younger individuals. This is how they learn where, how, and what to hunt, what to avoid, and how to communicate. These social behaviours can be seen in all dolphins – another reason why orcas fit right into this family group!
In conclusion, an orca is not really a whale even though it’s widely known as a “killer whale.” Rather, it’s a dolphin, since it shares so many physical features and behaviors with other dolphin species. So, when someone says that an orca is a whale, you can let them know why they’re actually dolphins!
Apex predator – A predator at the very top of the food chain
Echolocation – using reflected sound to locate objects
Matriline – A family line from a female ancestor
Taxonomy – The science of naming and classifying all the organisms on our planet
Unihemispheric sleep – A type of sleep where one half of the brain rests while the other is awake
Flesch Kincaid Grade Level: 7.1
Flesch Kincaid Reading Ease: 70.1
Cetacea (Whales, Dolphins and Porpoises) Retrieved November 10th, 2022 from
Delphinidae. Retrieved November 12th, 2022 from
Facts about orcas (killer whales). Retrieved November 10th, 2022 from https://uk.whales.org/whales-dolphins/facts-about-orcas/#:~:text=Orcas%20(also%20known%20as%20killer,found%20in%20every%20single%20ocean.
How do dolphins sleep? Retrieved November 14th, 2022 from https://uk.whales.org/whales-dolphins/how-do-dolphins-sleep/
Orca. Retrieved November 10th, 2022, from https://www.nationalgeographic.com/animals/mammals/facts/orca
Orcas: Facts about killer whales (2022, February 17). Live Science. https://www.livescience.com/27431-orcas-killer-whales.html
Sound Strategy: Hunting with the Southern Residents, part 2 (2020, June 15th) https://www.fisheries.noaa.gov/feature-story/sound-strategy-hunting-southern-residents-part-2#:~:text=The%20whales%20hunt%20with%20echolocation,bounce%20back%20to%20the%20whale.
Walker. 2007. Dolphins. Retrieved November 11th, 2022 from https://books.google.se/books?id=5Buh9FtAG8AC&pg=PA20&lpg=PA20&dq=dolphin+melon&source=bl&ots=flKTtPgN2g&sig=ACfU3U2gM2tpvkGJo_TEOeplxORZ55UzAQ&hl=en&sa=X&ved=2ahUKEwjpssbYxqj7AhVvx4sKHffcCGYQ6AF6BAhTEAM#v=onepage&q=dolphin%20melon&f=false
Whales, porpoises and dolphins – What’s the difference? Retrieved November 12th, 2022 from https://www.dcceew.gov.au/environment/marine/marine-species/cetaceans/whales-dolphins-porpoises