With the highly anticipated “Meg 2: The Trench” being released in early August, there is a certain buzz around the ancient shark that stars in the film alongside Jason Statham. Considered one of the largest and most powerful predators to have ever existed on Earth, it is no wonder this predator continues to fascinate people even millions of years after its extinction. A globally distributed species, found in oceans worldwide, it was a ferocious carnivore who primarily preyed on large marine mammals such as whales, seals, and other large fish – not people, as “The Meg” franchise has highlighted.
But there are still many mysteries around this shark, with what is known primarily about them coming from fossilized teeth, vertebrae, and occasionally other skeletal elements. And it is one of these elements that has led to a groundbreaking study that has shed new light on the lifestyle and biology of the icon. “Our big scientific findings come from ‘tiny evidence’ as small as grains of sand,” says DePaul University paleobiology professor Kenshu Shimada. Specifically, dermal denticles. Also known as placoid scales, they’re a unique type of scale found on sharks and other cartilaginous fishes, including rays and chimaeras. Unlike the typical scales found on bony fishes, which are thin and overlapping, dermal denticles are hard and tooth-like in structure. Varying by size, shape, density for each shark, they play a crucial role in the overall design and function.
So, what did these tiny scales show researchers about Megalodon?
Previously presumed to be an active, fast swimmer (similar to modern-day predacious sharks like the makos and great whites), research conducted by Shimada and his team challenges this belief. When examining tiny placoid scales of Megalodon found in rock pieces surrounding a previously described tooth set of the fossil shark from Japan, they noticed they lacked the narrow-spaced ridges or ‘keels’ that are characteristic of fast-swimming sharks. “This led my research team to consider O. megalodon to be an ‘average swimmer’ with occasional bursts of faster swimming for prey capture,” described Shimada. The finding also raises an intriguing paradox about how the warm-blooded Megalodon (a new research study that Shimada was also a part of) managed to expend the high level of metabolic heat associated with its endothermic nature without being an active swimmer.
While mammals and birds are the most well-known endotherms, some sharks also exhibit endothermic capabilities to varying degrees. Regional endothermy is known in some shark species, such as the great white shark (Carcharodon carcharias), thresher shark (Alopias spp.), and mako shark (Isurus spp.) to name a few. These sharks possess a network of blood vessels that help retain heat, allowing the warm blood leaving the muscles to transfer its heat to the cooler blood returning from the gills. This helps maintain a higher internal body temperature to specific regions, such as certain muscles or even the brain. This does lead to them maintaining higher metabolic rates, leading to increased activity and improved performance during hunting and feeding. But if Megalodon wasn’t an active swimmer, then why did it need this special adaptation?
Diving into the literature, the researchers stumbled upon a potential explanation that had been overlooked in the past—the role of endothermic body physiology in facilitating digestion and nutrient processing. “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,” said Shimada.
The team now believe that the giant shark was a relatively slow cruiser, utilizing its warm-bloodedness to aid digestion and nutrient absorption. To Shimada, it all “suddenly made perfect sense.”