It talked about how whales were doglike mammals tens of millions of years ago, and how they slowly changed their limbs to flippers, and became aquatic mammals.
It also talked about birds, elephants, and alligators.
Of course, birds are the descendants of dinosaurs. But they explained how feathers were used to regulate heat, and how wings slowly were used for gliding and then flight. And how originally there were only a few species of dinosaur that became birds, and now there are ten thousand species around the world.
Elephants originally were in almost every country, and went from hundreds of species to only three remaining. It showed how poachers killing elephants for their tusks has forced natural selection to produce elephants with much smaller tusks..or none at all.
Alligators and crocodiles used to be much larger and far more species. After the meteor hit 65 million years ago, the only species that survived were the smaller crocodiles that lived a partly aquatic life.
The special explained how genetic testing gave the common ancestors of all these animals, and helped put the fossils found in the correct evolutionary order.
If you're interested, the title is When Whales Walked The Earth I'm guessing it's available several places online.