Amelia Nichele
Amelia Nichele is a science journalist at The Royal Institution of Australia.
The megalodon (Otodus megalodon) has a long-standing reputation as one of the largest sharks to have roamed the oceans.
Now, US researchers have confirmed its sheer enormity, suggesting it grew up to 15 metres in length. That’s on a par with the extant current record holder, the whale shark (Rhincodon typus).
“For animals and especially sharks, their body size affects the range of travelling distances, predation risk, energy storage capacity and the extension of heat retention,” the researchers write in their paper in the journal Historical Biology.
“That may have in turn influenced their life history and behavioural strategies, tolerance level to extreme environmental conditions, predatory successes and mortality risks.”
O. megalodon lived around 15 to 3.6 million years ago, and fossil remains have been found along the coastlines and continental shelf regions of all continents except Antarctica. The species sat at the top of the food chain and fed on other large marine animals like whales and dolphins.
The shark group named Lamniformes, to which O. megalodon belongs, is well represented in the late Mesozoic-Cenozoic fossil record. However, their biology is poorly understood because they are mostly known from their teeth.
As a step to bridge this gap, the researchers used tooth, jaw and definition measurements from present-day non-planktivorous Lamniformes to formulate an equation that would allow an estimation of the megalodon’s body length.
The study demonstrates that the megalodon is an outlier because all other non-planktivorous sharks have a general size limit of 7 metres. Only a small number of plankton-eating sharks were equivalent or came close to its size.
As for how the megalodons became so big, the researchers suggest a combination of live-birth and cannibalistic egg-eating among early-hatched embryos may have led to larger sizes inside their mother.
“The increased physiological demands by embryos that grew to be sizeable lengths would have required the mother to feed more actively and possibly triggered certain species to evolve endothermy,” the authors write.
Mature males would have also needed to stay close to the size of mature females to ensure successful fertilisation.
The researchers say their work is a “critical advancement” in the understanding of the evolution of the ocean giant, as well as the ecosystems they existed in.
“Lamniforme sharks have represented major carnivores in oceans since the age of dinosaurs, so it is reasonable to assert that they must have played an important role in shaping the marine ecosystems we know today,” says lead author Kenshu Shimada, from DePaul University in Chicago.