Gigantic Megalodon sharks grew to much larger sizes in cooler waters, new study suggests

Megalodons, the iconic extinct sharks commonly portrayed as gigantic, monstrous beasts in films such as the 2018 sci-fi thriller The Meg, grew to larger sizes in cooler waters than in warmer areas, according to a new study.

The research, published on Sunday in the journal Historical Biology, sheds more light on how modern human-induced climate change may lead to shifts in marine habitats.

Otodus megalodon lived nearly worldwide about 15 million to 3.6 million years ago and is known only from teeth and vertebrae in the fossil record.

Scientists say the species was quite large, growing to at least 15m (50ft), and possibly as much as 20m (65ft), but a recent study also concluded that all previously proposed body forms of the giant shark remain nothing more than “speculation”.

In the new study, researchers, including those from DePaul University in the US, re-examined published records of geographic occurrences of Megalodon teeth along with their estimated total body lengths.

The findings of the new research suggest that individuals of O megalodon were on average larger in cooler water than those in warmer water.

“Our findings suggest a previously unrecognised body size pattern for the fossil shark, notably following a geography-driven ecological pattern known as Bergmann’s rule,” study co-author Kenshu Shimada said in a statement.

“Scientists constantly search for rules of life that help us predict natural patterns, and it seems that Bergmann’s rule applied to Otodus megalodon,” Victor Perez, a paleontologist at the Calvert Marine Museum in Maryland and co-author of the study, added.

This rule, introduced by German biologist Carl Bergmann in the mid-1800s, explains that larger animals thrive in cooler climates since their size helps them retain heat more efficiently compared to animals with smaller bodies.

While earlier research identified some Megalodon sites as possible nursery areas of the extinct shark as they yielded smaller fossil teeth on average relative to other sites, the new study suggests many of these previously discovered sites are located near the equator, where water is warmer.

“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,” Harry Maisch, another co-author of the study, noted.

Researchers believe the findings of the study have important implications for understanding how the ongoing climate crisis is rapidly accelerating marine habitat shifts to more polar latitudes in apex predators such as sharks.

“The main conclusion of this study is that not all geographically different Megalodon individuals grew to gigantic sizes equally. The common notion that the species reached 18–20 m in total length should be applied primarily to populations that inhabited cooler environments,” Shimada added.