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.