The Otodus megalodon, commonly called the megalodon, is famous for its massive size. Weighing up to 50 tons and measuring up to about 60 feet in length, the meg was the largest shark ever to exist.
But a new study published in Historical Biology found not all megalodons reached such gargantuan sizes. Instead, size varied based on geography, with the larger individuals living in colder areas.
Researchers re-examined body size trends and proposed nursery areas from previous studies. Formerly, areas in warmer waters were thought to be nurseries because scientists found evidence of smaller sized megalodons living in those regions.
“It is still possible that O. megalodon could have utilized nursery areas to raise young sharks. But our study shows that fossil localities consisting of smaller megalodon teeth may instead be a product of individual sharks attaining smaller overall body sizes simply as a result of warmer water,” says study author Harry Maisch from Bergen Community College and Fairleigh Dickinson University in a statement.
The authors also noted a “curious body size pattern across different populations of O. megalodon that has never been reported to date,” per the study. The pattern follows what’s known as Bergmann’s rule. Named after German biologist Carl Bergmann, the rule states that generally, within a species, larger animals can be found in colder climates because bigger organisms retain heat better.
“Our study may well represent the first possible case of Bergmann’s rule demonstrated for elasmobranchs [cartilaginous fishes] if our data interpretation is correct,” write the authors.
Megalodons lived about 3.6 to 23 million years ago, per Smithsonian’s Ocean Portal. Their skeletons were mostly cartilage, which is difficult to fossilize. Most of what scientists know about these predators comes from their teeth, vertebrae or fossilized poop. Teeth are valuable because sharks constantly shed and replace them, leaving behind ample evidence of how they interacted with their environment,
“Teeth are really important,” Meghan Balk, a researcher of paleobiology at the Smithsonian’s National Museum of Natural History who has studied megalodon, told Smithsonian magazine’s Katherine J. Wu in 2018. “They interact with the environment and [show] how the animal feeds. They’re the best proxy we have [for these traits].”
Per the study, the most reliable tooth-based estimates of the megalodon’s total length come from the animal’s upper anterior teeth. The authors excluded all teeth that yielded less reliable estimates of megalodon length from previous studies in the new paper.
The scientists say this study could help researchers understand how climate change is affecting creatures in the ocean today.
“The results of this study have important implications for understanding how modern climate change is rapidly accelerating marine habitat shifts to more polar latitudes in apex predators such as sharks,” says study author Michael Griffiths, a professor of environmental science at William Paterson University Michael Griffiths in the statement.