Ever wonder why whales such as the Blue Whale and the Baleen Whale have gotten so big they're now the largest mammals on Earth?

The fact they eat tons of krill and plankton is a major reason. But frequently overlooked is that whales today have no natural predators.

Sure Killer Whales do kill other whales such as baleens (80 feet long) but the size of an Orca (around 30 feet long) doesn't make them a threat to entire whale family. Not so from 16 to 2.6 million years ago when the biggest shark that ever lived chowed-down on whales and kept their numbers in check.

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Megalodon (Carcharocles megalodon) ranged in size from 45 feet to 60 feet, not far off from today's Blue Whale with a length of about 100 feet. Megalodon is best described as an super-sized Great White (20 feet long) that seemed to have a liking for baleens.

Fossils of baleen whales are often found along with Megalodon teeth. The word Megalodon, by the way, means "big tooth". The largest Megalodon teeth found measured seven inches.

Scientists point out baleen whales at the time Megalodon ruled the waves were much smaller in size than they are today. The same can be said for other whale species today. The question is "Why"?

"When we found out when that happened, we noticed it coincided with the pattern mentioned in whales. Now we need to find out if one event - Megalodon's extinction - caused the other - evolution of gigantism in whales", said Catalina Pimiento from the Florida Museum of Natural History who co-authored a study about megalodon and why today's whale reached their enormous sizes.

She noted this was a first step in ongoing research to understand the disappearance of Megalodon.

"From modern sharks, it is known that larger individuals have a broader range of prey size, including larger prey. That means that the larger prey will be predated mostly by larger sharks."

She noted that after megalodon's extinction 2.6 million years ago between the Pliocene and Pleistocene epochs, baleen whales began to grow to their gigantic sizes today.

The findings were published in the journal, Plos One.