Bones aren't the only evidence of whale evolution. Their ancestry is also visible in the way they move.
Frank E. Fish, "The big question is how do you go from a terrestrial mammal that ran around on all four legs, to something such as a dolphin, which now doesn't have any legs at all, and is well adapted to swimming in the oceans."
Even though whales look like fish, they don't swim like them.
Fish swim by flexing their spines from side to side, like this shark.
But mammals swim differently.
This otter swims by ungulating its spine up and down in exactly the same way that whales do. And, as it turns out, in the same way that land mammals use their spines when running.
Whales took with them into the water, their ancestral way of moving and we can still see it 50 million years later.
Neil Shubin, "In one sense Evolution didn't invent anything new with whales, it was just tinkering with land mammals. It's using the old, to make the new. We call that tinkering, and it does this in every animal group, at every time, during evolutionary history."
All images and extracts from NOVA, WGBH Boston, PBS Television |