The intermediate states between an ancestral form and that of its
descendants are transitional fossils.
What is a transitional fossil?
Transitional fossils are remains of an organism that came in between a known version of a species and the current species.
Transitional fossils would be proof of evolution because they would show medium forms of a species and they altered and accumulated adaptations at a slow pace.
Thus, option "D" transitional fossils are correct.
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