Question

Whales have what seem like remnants of a pelvis and femur, as shown here. What are these structures an example of?

Answer 1

In short, the answer Vestigial structures.

Good luck!

-RxL

Answer 2

vestigial limbs

vestigial limbs are the remnants from the development of any one organism's ancestors. 

Humans, for one example, have no real need for an appendix now that we are no longer herbivores. 

Look at a x-ray image of certain snakes and you can see the structural remains of feet.