They've evolved to be round so that they can swivel to spot delicious prey and easily roll when your cousin talks about his new car for the third time.
Fennec foxes use their large, swiveling ears to rapidly home in on activity beneath Sahara sands, while bat-eared foxes can pick up savanna sounds as slight as termites crawling and munching on grasses.
Throughout the 1800s, several improvements made these newfangled wheelchairs even better, like rear wheels and casters — which are wheels that can swivel like on a shopping cart.