The most commonly accepted theory involves this bad boy:
The Megalodon ( Carcharodon megalodon ).
Ancient whales were actually quite small, about the size of a dolphin or slightly larger. They lived in large numbers and fared well. However, unlike today's whales, they faced a constant threat: the megalodon.
Megalodon is believed to have consistently hunted these smaller whales, with theories about the actual evolutionary process including some of the following:
- Eat the whale. Swallow it alive and in pieces.
- Disable the poor thing by biting its fins, preventing its escape and ensuring its death.
- The process that great white sharks still use today: taking large bites out of the animal while it is alive, killing or disabling it being irrelevant for such large hunters.
Of course, we can't know for sure based on fossil evidence alone.
Now let's get back to the topic at hand: what did megalodon have to do with whales becoming enormous? This is where evolutionary theory and natural selection come into play.
Megalodon would likely have targeted the slowest and largest whales. The smaller, faster whales that managed to elude it were more likely to survive and pass on their genes, producing equally small, fast calves. Any larger whales would have been slaughtered.
Megalodon essentially kept them small, much like a human keeps his lawn mowed.
However, once the megalodons became extinct (scientists believe this was the result of a cooling period in Earth's history about 2.6 million years ago), there was no predator to keep the whales' size in check. No one to "mow the lawn."
Slowly, larger whales emerged. And it turned out that the larger whales fared better in terms of food acquisition, mating, and overall survival. Small whales didn't become extinct, as we still see today in porpoises, narwhals, and dolphins. Large whales came to dominate the cetacean niche.
So what's the point here?
The disappearance of this big guy
led to the creation of enormous new beasts, including the largest animal ever to exist on planet Earth. (YES, NEVER! I.E., NO ANIMAL HAS EVER BEEN BIGGEST IN HISTORY!)
Sadly, this gentle giant is at risk of extinction due to human activity.
So let's forget about it: the Megalodon ate whales. When the Megalodons disappeared, the whales became enormous.
Whales eat krill (mostly).
So here we are. The extinction of the megalodon is at the origin of the creation of enormous whales.