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Why do animals have tails? Kristin M., 11, Kansas City, Missouri
Scientists have found fossils of animals with tails dating back hundreds of millions of years. Early fish then used their fan-like tails as fins to swim across the oceans and escape predators.
As these fish evolved into land-dwelling creatures, their tails also began to change.
Whether they belong to reptiles, insects, birds or mammals, tails serve a wide variety of purposes. Modern animals use their tails for everything from balance to communication to finding mates.
It helps with balance and movement
Scientists believe that dinosaurs, including Tyrannosaurus rex, moved their tails from side to side to balance their heavy heads and bodies while walking on two legs. This movement allowed them to run fast enough to catch their prey.
Similarly, today’s kangaroos use their tails for balance when jumping across open land. But they don’t just use it to counterbalance their weight: the kangaroo’s tail also doubles as a powerful third leg that can help propel them through the air.
Cats and other climbing animals often have bushy or long tails that help them balance, like a tightrope walker holding a long pole.
Monkeys use their long tails to keep their balance while swinging between the branches of forest trees. Many have prehensile tails or grips that act like hands and allow them to hold on to tree limbs.
These tails are so strong that they can even hold the animal while eating fruit and leaves.
A tyrannosaurus rex could swing its heavy tail to balance itself while walking.
A defensive mechanism
The tails of other animals became weapons. For example, stingrays have a stinger tail that they can use as a defense when attacked by a predator.
Venomous rattlesnakes have knobs of dry skin on their tails that make a racket when shaken. This alerts any animal that might threaten the rattlesnake that it is preparing to strike.
Many insects also have tails, but they evolved separately from other animals with backbones, such as fish and mammals. Most tailed insects use their tails to lay eggs or to sting and paralyze hosts or prey. In some animals, such as wasps, their tails can do both, as certain parasitic wasps will lay their eggs inside a host.
Grazing animals, such as American bison and the wildebeest and giraffes of Africa, have tails with tufts of long hair that can be swung like a beater to remove mosquitoes and other insects that might bother them. Domestic cows and horses also have this type of tail.
Rattlesnakes have tails that evolved for defensive purposes. Paul Starosta/Stone via Getty Images
A communication assistant
Birds use their feathery tails both to balance themselves while perched on a tree branch and to steer and reduce drag while flying. Some birds also use their tail as a mating display.
This visual display is most noticeable in species such as turkeys and peacocks: male turkeys and peacocks will display their colorful tail feathers to attract females.
Animals that live and hunt in groups or packs, such as wolves, use various tail positions to indicate their rank.
Dogs, which descended from wolves, also use their tails for communication. You’ve probably seen dogs wagging their tails when they’re excited.
Why don’t you have one
Although humans don’t have a long tail like monkeys, or a vibrant tail of feathers like peacocks, our ancestors did have tails.
Scientists believe that these tails disappeared from our human ancestors about 20 million years ago. Once they started walking upright, they no longer needed tails to help them balance.
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