A squirrel, a zebra, a deer, a wolf, and a grizzly bear meet in a field. Yes, a disaster in the making, but also a bunch of quadrupeds — animals that walk on four feet.
Cut quadruped in half and it makes sense: quadru means four, like when a woman births four babies they are called quadruplets. And –ped is for the feet: think of centipedes and millipedes, insects that have so many feet it’s disturbing. A human is a biped because they walk on two feet. If you meet a human with four feet, you could call him a quadruped. You could also call the circus and let them know their quadruped is loose.