So, I'm assuming you need to complete this analogy - biped: quadruped::ostrich:?
So, a biped is an animal which walks using two legs only; on the other hand, a quadruped animal uses all four limbs to walk. If an ostrich is a biped, meaning it walks on two legs, then you need a quadruped animal to complete the analogy. Humans aren't quadruped - they are bipeds, so you'd need an animal such as cat, or dog, or something like that.