A close cousin of megalodon -- the largest shark that ever lived -- has been identified using remains found in California, North Carolina, Peru and Japan.

The shark, Megalolamna paradoxodon, lived 20 million years ago and had impressive 2-inch-long teeth. The new find (its name means "paradoxical Teeth") also reveals important information about megalodon and existing great white sharks.

Great whites are not direct descendants of the enormous megalodon, which could grow to well over 33 feet long. (Some researchers even think it could grow up to 67 feet long, or about five car lengths.) However, according to research published in the journal Historical Biology, great whites have taken the place of megalodon at the top of the ocean's food chain.

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Lead author Kenshu Shimada explained that megatoothed sharks and modern great white sharks belong to the shark group called Lamniformes. However, a split must have taken place deep in time and each lineage took its own evolutionary path.

"So, it is erroneous to say that the modern great white shark evolved from the megalodon," said Shimada, a paleobiologist at DePaul University and a research associate at the Sternberg Museum in Kansas.

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"The earliest forms of the great white shark coexisted with megalodon," Shimada said, "but as megalodon dwindled down and became extinct, the way we can look at it is that the great white shark took over the ecological role of megalodon and became the 'superpredator' of the modern seas."

Megalolamna co-existed with megalodon too. At about 13 feet long, it was much smaller than megalodon, but it had grasping front teeth and cutting rear teeth that would have torn into tough flesh with relative ease.

"Size-wise, megalodon could have preyed upon megalolamna, but such occurrences must have been very rare, considering the fact that megalolamna is an exceptionally rare shark based on the fossil record," Shimada said, explaining that only about a dozen teeth for it have been found.

He and his colleagues think megalolamna feasted on medium-sized fish, which could have included other sharks.

As for why its teeth were found at places as distant as California and Japan, he believes that megalolamna had a wide geographic range.

A map shows where Megalolamna teeth were discovered. Kenshu Shimada

Its teeth resemble oversized versions of modern salmon sharks', which belongs in the genus Lamna.

Yet another genus, Otodus, comes into play with these megatoothed sharks. Shimada and his team now believe that megalodon belongs in the genus Otodus, which emerged soon after the Dinosaur Age 60-65 million years ago. Instead of being Carcharodon megalodon, the researchers refer to megalodon as Otodus megalodon.

"The earliest species of Otodus were smaller than Otodus megalodon, but they still included relatively large forms based on preserved robust teeth that are suggestive of feeding on large prey," Shimada said.

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Matthias Epple of the University of Duisburg-Essen said that megatoothed sharks, like modern great whites, had teeth consisting of fluoroapatite. This is a hard mineral that forms in tooth enamel exposed to fluoride and helps prevent decay by its resistance to acidity.

"You might say that these sharks used 'built-in toothpaste,'" Epple said.

Megalolmna had another thing in common with great whites: its size. Great white sharks today can grow to over 13 feet long. Megalodon's much larger size could have been affected by climate, according to Shimada and his team, who report that both megalolamna and megalodon emerged during a particularly warm period of Earth's history.

Shimada plans to study climate change in relation to the body size of sharks and other animals, to see what might be in store as average global temperatures rise.