vestige: a part or organ of an organism that has become reduced or functionless in the course of evolution.

When whales evolved from land animals their hind limbs gradually disappeared because they were no longer necessary. Sometimes a whale will be born with vestiges of hind limbs. Creationists can't explain this fact. They can't even lie about this one but that won't stop them from trying. It's not easy for evolution deniers to defend their stupidity these days. It would be so much easier for them to grow up and face facts. Unfortunately their brain damage can't be fixed.

Early Whales Had Legs "The ancestors of whales once strode on land on four legs, just as other mammals do. Over time, as they evolved to dwell in water, their front legs became flippers while they lost their back legs and hips, although modern whales all still retain traces of pelvises, and occasionally throwbacks are born with vestiges of hind limbs."