The megatooth shark Otodus megalodon roamed the world’s oceans approximately 23 to 3.6 million years ago.
Despite its fame in pop-culture, surprisingly little is known about this animal. Scientists have long debated, based on fragmentary remains and fossil teeth, on the species’ life-appearance and size. Often depicted as a super-sized white shark, an anatomical study published in 2020 concluded that the species was more closely related to the modern mako shark (Isurus oxyrinchus) and the living animal’s length is thought nowadays to be about 20 meters – likely the maximum size sharks can get.
Evolutionary adaptions including warm-bloodedness (an organism’s ability to maintain a relatively constant internal temperature) likely led to this gigantism.
But a new study reveals the the living animal was a rather slow cruiser that used its warm-bloodedness to facilitate digestion and absorption of nutrients.
The new study is based on the discovery of tiny scales, more precisely called “placoid scales,” of O. megalodon within rock pieces surrounding a previously described fossil tooth set from Japan.
Placoid scales are made from a bone-like material and cover the entire body surface. Their characteristic form plays an important role in the hydrodynamic properties of the shark’s skin. Narrowly-spaced ridges are distinctive anatomical features of fast-swimming sharks. The ridges act as a myriad of microscopic keels reducing turbulence and friction as the shark moves through the water. But the ridges on the placoids of O. megalodon are only poorly developed.
“This led my research team to consider O. megalodon to be an ‘average swimmer’ with occasional bursts of faster swimming for prey capture,” concludes lead author Kenshu Shimada, paleobiology professor at Chicago’s DePaul University.
As the living shark didn’t need to keep its body temperature over water temperature to be an active swimmer, the authors suggest an alternative evolutionary advantage of this species’ warm-bloodedness.
“Otodus megalodon must have swallowed large pieces of food, so it is quite possible that the fossil shark achieved the gigantism to invest its endothermic metabolism to promote visceral food processing,” explains Shimada.
A large body able to conserve its inner temperature, especially around the stomach and intestine, could have facilitated digestion as well as absorbing and processing nutrients.
The study “A Multi-Technique Analysis of Surface Materials From Blood Falls, Antarctica” was published in Historical Biology (2023). Additional material provided by Taylor & Francis.
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