Tides, Depths & Reefs
The physics of the sea and the life that adapted to it.
What is the deepest known point in the ocean?
Whales and dolphins are land animals that returned to the sea and had to solve every problem again from scratch. These ten questions cover how they feed, breathe and communicate.
Cetaceans are mammals, which means every one of them has to surface to breathe, give birth in the water and keep warm without any help from the sea around it. Almost everything odd about them follows from that: the blowhole moved to the top of the head, the forelimbs became flippers, and a thick layer of blubber took over from fur. This quiz splits roughly along the line that divides the group in two — the baleen whales that filter small prey in bulk, and the toothed whales, dolphins and porpoises that hunt individual animals using sound. Knowing which side a species falls on answers a surprising number of the questions.
Every question in this quiz is listed below with its correct answer and the reasoning behind it. Play first if you would rather not see the answers — or read through as a study sheet.
Play it insteadAnswer: D. It takes in mouthfuls of water and strains small animals out through fringed plates
Why: Baleen plates hang from the upper jaw and act as a sieve, letting the whale live on animals a tiny fraction of its own size. The plates are made of keratin, the same material as fingernails and hair.
Answer: C. The narwhal
Why: The tusk is an overgrown left canine tooth that grows straight through the animal's upper lip, usually in males. Traded as unicorn horn in medieval Europe, it turns out to be packed with nerve endings.
Answer: B. Only the males
Why: A song can run for twenty minutes and be repeated for hours at a stretch. Every male in a population sings the same version, and that version drifts and changes over the course of a season.
Answer: A. Two
Why: All baleen whales have paired blowholes, which is why their blow often looks like a broad V from a distance. Toothed whales, including dolphins and the sperm whale, have only one.
Answer: D. The sperm whale
Why: Sperm whales routinely work well below 1,000 metres and can stay under for around an hour. They also have the largest brain of any animal that has ever been measured.
Answer: C. Producing and focusing the loud clicks it uses to find prey
Why: The organ holds a waxy oil that helps shape the animal's clicks into a narrow, powerful beam. Whalers hunted the species almost entirely for that oil, which burned cleanly in lamps and candles.
Answer: B. One half of the brain rests at a time while the other half stays alert
Why: Breathing in a dolphin is a conscious act rather than an automatic one, so shutting down the whole brain would drown it. A sleeping dolphin usually keeps the eye opposite the resting half of its brain closed.
Answer: A. A blunt head with no beak and flattened, spade-shaped teeth
Why: Porpoises are generally smaller, stockier and far less inclined to approach boats. There are only around seven porpoise species against roughly forty of dolphins.
Answer: D. Arctic feeding grounds and the lagoons of Baja California
Why: The round trip runs to something like 16,000 kilometres a year along the Pacific coast of North America. Greys also feed unusually for baleen whales, rolling onto one side and sieving mouthfuls of sea-floor mud.
Answer: C. Hippopotamuses and other even-toed hoofed mammals
Why: Genetic work places cetaceans firmly inside the even-toed ungulates, with hippos as their nearest living relatives. Early whale fossils back this up, preserving distinctive ankle bones shared with that group.
Staying warm, finding the way home, sleeping safely. Every species faces the same short list, and the answers are inventive.
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