These structures examples of vestigial structures.
The vestigial structure is the structures which used to play an important functional role in the body of the ancestor species. But with due to course of evolution the structures have been adapted by the descendants but are functionless. These structures are typically in the rudimentary and degenerative condition. Appendix, wisdom tooth and sinuses are the examples of some of the vestigial structures.
They're vestigial structures (meaning they're "left over" from some ancestor species of the whale). In the whale's ancestor species, the pelvis and femur were functional; over time, as the whale started living in the ocean and they became unnecessary, the pelvis and femur shrunk into what they are now.
Thus, vestigial structures are the answer.
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