Many organisms have body parts that have no function at all.
Humans for example have a complete set of muscles to wiggle their ears just like a coyote does. Whales, the largest group of mammals, have pelvic bones but these bones serve no function. Some of these structures are also briefly present during embrionic development . It is easy to interpret the presence of these structures as leftovers from the evolutionary past. These structures show which group of animals and plants share common ancestors.