We've been able to piece together many of these changes thanks to transitional fossils.

We know much of the remarkable evolutionary story of whales thanks to transitional fossils.

And given that every species alive today has fossils related to its ancestry, that’s a lot of transitional fossils.

The transition itself can only be illustrated and corroborated by transitional fossils, which never demonstrate an exact half-way point between clearly divergent forms.

Thus, the transition itself can only be illustrated and corroborated by transitional fossils, but it will never be known in detail.