Marine Mammals
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50 free Marine Mammals trivia questions with answers — trivia quiz, new questions added Oct 2026.
Marine mammals breathe air, nurse their young and keep a warm body, yet they spend most or all of their lives in salt water. That takes some remarkable engineering: bodies that hold heat in freezing seas, lungs and muscles that allow dives far longer than any human could manage, and senses tuned to a world where light fades quickly. This quiz covers the whole cast. Expect questions on cetaceans (the whales and dolphins), sirenians (the gentle, grazing sea cows), the seals and their relatives, and the few other mammals that depend on the ocean. Along the way it asks how these animals stay warm, find food, talk to one another and rest without drowning, and where they came from. It is written for curious players of any age, from elementary pupils learning about animal adaptations to adults who never miss a nature documentary. Most questions can be worked out with a little thought, and every answer comes with a short explanation.
30 of 50 questions with answers and explanations. Play the quiz
Q 01Which thick layer under the skin keeps whales and seals warm in icy seas and helps them float?
Blubber
Blubber can be more than 30 centimetres thick on the biggest whales and make up as much as half of an animal's body mass at some points in its life.
Q 02Which ocean giant, whose heart alone can weigh about 180 kilograms, is the largest animal known ever to have existed?
Blue whale
The blue whale reaches about 30 metres and 200 tonnes, yet it lives almost entirely on tiny shrimp-like animals strained from the sea.
Q 03Which Arctic whale carries a long spiral tusk that is really a canine tooth growing out through the upper lip?
Narwhal
The narwhal's tusk fed a medieval belief that it was the horn of the legendary unicorn. Females rarely grow one, and a few males grow two.
Q 04Which marine mammal is a keystone species of kelp forests because it eats the spiny urchins that graze them bare?
Sea otter
The sea otter also has the densest fur of any animal, and it is one of the few mammals to use tools, cracking open shells with rocks.
Q 05Which Arctic hunter of seals is counted as a marine mammal because it depends so heavily on the ocean?
Polar bear
The polar bear's scientific name, Ursus maritimus, is Latin for 'sea bear'. One study found the bears swimming for an average of 3.4 days at a stretch.
Q 06Which mythical creatures did Christopher Columbus report off Hispaniola in 1493, having probably seen manatees?
Mermaids
Mermaids, Columbus wrote, were not as beautiful as painters made them. Sea cows still carry the legend in the name of their order, Sirenia, after the sirens of Greek myth.
Q 07Which sense lets dolphins find fish in dark water by sending out clicks and listening for the returning sound?
Echolocation
Echolocation in dolphins sends a focused beam of clicks out through the forehead, and the returning sound is picked up through the lower jaw.
Q 08Which black-and-white hunter is, despite the common name, the largest member of the oceanic dolphin family?
Killer whale
The killer whale, or orca, is one of the few animals whose females go through menopause, living for decades afterwards as the heads of their family groups.
Q 09DNA evidence shows which large African land mammal is the closest living relative of whales and dolphins?
Hippopotamus
The hippopotamus shared an ancestor with the whales until about 55 million years ago, which makes hippos closer kin to dolphins than to pigs.
Q 10How do dolphins keep surfacing to breathe while asleep, when each breath is a deliberate act?
Half the brain stays awake
Half the brain stays awake while the other half sleeps, leaving a dolphin just conscious enough to breathe and to watch for predators.
Q 11Which comb-like plates, made of the same keratin as human fingernails, let the largest whales strain food from seawater?
Baleen
Baleen hangs in rows from the upper jaw in place of teeth. Under the misleading name whalebone, it once stiffened corset stays, collars and parasol ribs.
Q 12Which deep-diving giant, the largest toothed predator on Earth, also has the biggest brain of any animal?
Sperm whale
The sperm whale carries a brain more than five times heavier than a human's, and its clicks are the loudest sounds made by any animal.
Q 13Which shrimp-like crustaceans, swarming in huge numbers off Antarctica, are the main food of filter-feeding whales?
Krill
Q 21Which land giants, along with the little hyraxes, are the closest living relatives of the sea cows?
Elephants
Elephants share a telling quirk with manatees: both keep replacing their teeth through life, with new ones moving forward from the back of the jaw.
Q 22Which marine mammal, the only plant-eater living strictly in the sea, has a fluked tail like a dolphin's?
Dugong
The dugong grazes on seagrass meadows, and it stands alone because every species of manatee uses fresh water to some degree.
Q 23Which giant kelp-eating marine mammal of the Bering Sea was hunted to extinction within 27 years of its 1741 discovery?
Steller's sea cow
Krill swarms can pack tens of thousands of animals into a single cubic metre, and the Antarctic species alone adds up to hundreds of millions of tonnes.
Q 14Which Arctic giant may live for more than 200 years, the longest lifespan known for any mammal?
Bowhead whale
The bowhead whale is named for its massive skull, which it uses to break up through Arctic ice, and it has the largest mouth of any animal.
Q 15Which sea giant is known for the males' long, complex songs and for herding fish inside rings of bubbles?
Humpback whale
The humpback whale's bubble nets are counted as a form of tool use, and a single song by a male can run for more than half an hour.
Q 16Which white Arctic cetacean is nicknamed the sea canary for its high-pitched squeaks, squeals and clucks?
Beluga whale
The beluga whale has no fin on its back, which lets it swim easily beneath sea ice, and its name comes from the Russian word for white.
Q 17What is the name for the nostril on top of a whale's head, which moved there from the snout during evolution?
Blowhole
The blowhole is a single opening in toothed whales and a pair in the great filter feeders, and the stale air blown out of it forms the steamy spout.
Q 18Which fruit shares its name with the rounded forehead organ that toothed whales use to focus their sound beams?
Melon
The melon works like a lens for sound, bending the animal's clicks into a narrow beam aimed wherever the head is pointing.
Q 19Which waxy substance, formed in the gut of a deep-diving whale, was long prized by perfume makers?
Ambergris
Ambergris makes a scent last much longer on the skin, though perfumers have mostly replaced it with a synthetic copy.
Q 20Which colour do adult Amazon river dolphins, known as botos, take on as years of scrapes wear at the skin?
Pink
Pink shows most strongly in males, which pick up more scars from fighting one another. The boto is also the largest of the river dolphins.
Steller's sea cow was first described by Georg Steller while he was shipwrecked on Bering Island, and it was slow and easy for hunters to catch.
Q 24Which US state named the manatee its official marine mammal and shelters hundreds each winter in warm spring-fed rivers?
Florida
Florida's manatees also crowd around the warm-water outflows of coastal power plants in winter instead of migrating south as they once did.
Q 25Unlike fish, whales and dolphins drive themselves forward by beating their horizontal tails in which direction?
Up and down
Up and down beats of a flat, horizontal fluke push a whale along, whereas a fish sweeps an upright tail fin from one flank to the other.
Q 26Which body parts did the land-dwelling ancestors of whales lose, leaving only small hidden bones near the pelvis?
Hind legs
Hind legs vanished as whales took to the sea, while the front limbs turned into flippers used to paddle and steer.
Q 27Which Arctic animal's scientific name, Odobenus, means 'tooth-walker' in Greek, after the way it hauls out onto ice?
Walrus
The walrus really does use its tusks to climb out of the water, and it also uses them to make and keep open breathing holes in the ice.
Q 28Which marine mammals have small external ear flaps, long front flippers and the ability to walk on all fours?
Sea lions
Sea lions can pull their back flippers under the body to walk on them, while true seals cannot and must wriggle along on their bellies.
Q 29Which Antarctic hunter, an apex predator with massive jaws, catches penguins by lurking at the edge of the ice?
Leopard seal
The leopard seal also preys on other seals, and it is the second largest seal in the Antarctic.
Q 30Which vast Siberian lake has a seal of its own, found nowhere else and living only in fresh water?
Baikal
Baikal's seal is one of the smallest true seals, and it lives mainly on the golomyanka, an oily fish found only in the same waters.