Long ago, an almost unimaginably large shark called megalodon terrorized the waters.
It didn't make the evolutionary cut, though, and researchers now believe that it being wiped off the face of the Earth may be what allowed some whales to get so big, according to BBC.
The first step towards arriving at this theory was reassessing exactly when it was that the 60-ton predators disappeared. Despite the wealth of remains available for study, it has proven tough to pinpoint when the final days of megalodon actually were.
Previous best guesses estimated that the shark's demise happened about 1.5 million years back. Now researchers are saying it took place closer to two-and-a-half million years ago. Probably not by coincidence, that's right around the time whales, specifically those of the baleen variety, started to get bigger.
Mega-shark extinction linked to whales' current size
FILE - In this undated file publicity image provided by Discovery Channel, a great white shark swims near Guadalupe Island off the coast of Mexico. The Discovery network special âMegalodon: The Monster Shark Lives,â opened Discoveryâs annual âShark Weekâ on Sunday, Aug. 4, 2013. With an estimated 4.8 million viewers, it had the largest audience of any show in the 26 years that Discovery has made âShark Weekâ a part of its summer programming, the Nielsen company said. (AP Photo/Discovery Channel, Andrew Brandy Casagrande, File)
Steve Alten signs a copy of his book "Meg: Primal Waters" at the Book Expo America convention, Saturday, June 5, 2004, in Chicago. Alten is standing in front of the jaws of a Megalodon shark, a prehistoric 70-foot shark which plays the beast in Alten's new novel. (AP Photo/Brian Kersey)
Children of a kindergarten admire the giant mouth of a primeval Megalodon shark model at the Natural History Museum in Schleusingen, central Germany, Friday, July 4, 2014. The model is part of the special exhibition 'Sharks' . (AP Photo/Jens Meyer)
A tooth of an extinct giant shark called 'Carcharodon megalodon' found by paleontologists during a project to recover fossils during the Panama Canal expansion, is displayed after a news conference in Panama City, Friday, April 26, 2013. A group of scientists and paleontologists have completed a project with the Panama Canal Authority to recover fossils of at least ten new species of animals that inhabited the earth millions of years ago. (AP Photo/Arnulfo Franco)
UNSPECIFIED - CIRCA 2003: Reconstruction of Megalodon, (Carcharodon megalodon) extinct species of shark which lived between the Eocene and the Pliocene Period. Drawing. (Photo by DeAgostini/Getty Images)
UNITED STATES - MARCH 03: A person holds the fossilized tooth of a prehistoric giant shark, Maryland (Photo by J. Baylor Roberts/National Geographic/Getty Images)
Fossilized teeth of the giant shark, the 60 feet long Carcharodon megalodon, From Malta. (Photo by: Desmond Morris Collection/UIG via Getty Images)
Author Steve Alten, a Philadelphia native, examines fossil teeth inside the reconstructed jaws of a "Carcharodon megalodon," a prehistoric shark, at the New Jersey State Aquarium, in Camden, N.J., Thursday, June 26, 1997. The first-time novelist's book ,"Meg," is about a megalodon which emerges from the ocean's depths to menace 20th century Hawaii and Southern California. (AP Photo/Allen Oliver)
In this March 16, 2011, photo children look at the Shark Jaw of a Megalodon, a prehistoric shark, at the Museum of Nature and Science in Dallas. The jaw is 11 feet wide and almost 9 feet tall, it consists of 182 teeth collected from South Carolina rivers. The jaws go on sale in June at Heritage Auctions in Dalas _ the starting bid is $625,000. (AP Photo/Rich Matthews)
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Marine mammals likely constituted a big part of megalodon's menu, so with it gone, they were free to thrive. Observations indicate that in the years since the mega-shark's extinction, baleen whales' physical mass has increased significantly. They can now reach up to almost a hundred feet in length.
The science behind the theory hasn't been verified, and researchers say further investigation into the possible connection is needed.