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A Tale of Tails: Why Do Animals Have Them (and Why Don’t We)?

November 4, 2018 GMT

By Sally Cragin

Dear Pet Talk: Why do animals have tails? -- Austin, third grade, Fitchburg

Dear Austin: Tails are amazing. Do you wish you had one? If you love climbing trees, you could use a prehensile tail, such as opossums have. If you want to escape predators quickly, a tail that disconnects would help save you if you were a gecko.

Tails are part of the evolutionary package for many mammals. For dogs and cats, tails help provide balance and offer an additional means of communication.

When we speak to kids about pets, we talk about “reading” a pet’s tail. A dog’s tail that is wagging vigorously, along with a happy “smile” on the dog means your pup is happy. A tail that is low could indicate uncertainty or fear.

With a cat, a tail that is flicking quickly back and forth shows annoyance. And a cat who has her tail fluffed out and erect, along with ears back, is a puss that is not to be messed with.

Tails can also entertain an animal, and a dog or cat chasing its tail is a sight to see.

So why don’t humans have tails? We are bipedal, and like the “great apes,” walk on two legs, so we don’t need a tail for balance. However, all of us did have a tail once. We grow one between day 31 to 35 of fetal development. It then regresses and fuses into vertebrae that form our coccyx, or “tail bone,” as it is sometimes referred.

Sally Cragin is the director of Be PAWSitive: Therapy Pets and Community Education. Send questions to .