Researchers have found that the megalodon (Otodus megalodon) and great white sharks (Carcharodon carcharias) likely shared a similar position in the food chain (at the top!), and both species appeared to enjoy similar foods, including cetaceans (marine mammals) such as whales, dolphins and porpoises.
“One of the main challenges that palaeontologists face is reconstructing the biology (e.g., behavior, ecology, trophic position) of extinct animals,” says Dr Mohamad Bazzi, shark biologist and palaeontologist from the University of Zurich, Switzerland.
“Studying ancient animals through the lens of their modern counterparts, as this study does, however, demonstrates the enormous potential for ecological insight. More specifically, the inclusion of living species shows how to ground-truth ecological interpretations of the past.”
The researchers made their finding by looking at zinc isotopes in teeth of living sharks and bony fish, and comparing these patterns to fossil sharks, including 13 megalodon specimens. Zinc is incorporated into the enamel of an animal’s teeth when they form and can be used as a proxy for predicting what an animal ate, and therefore, what trophic level it filled within an ecosystem.
“It comes as no surprise that the gigantic Otodus megalodon occupied the upper tier of oceanic systems,” says Bazzi. “Nonetheless, the finding that zinc isotope ratios reflect trophic status in sharks is a major step towards reconstructing past marine ecosystems, especially for animals whose fossil remains commonly comprise shed teeth. This also complements assessments of tooth shape and size, which have also been shown to reflect the feeding ecology of both living and extinct sharks.”
“It seems that the diets of megalodon are relatively consistent with the diet of the great white, and that has been the long-standing suspicion based on the shape of their teeth,” says Dr Nicolas Campione, from University New England in New South Wales, who has worked on the morphology of fossil shark teeth.
“It’s comforting to see that the shape of the teeth and their chemical composition support each other, suggesting that we are all on the right track when interpreting megalodon as an apex predator, although I guess maybe this is not so surprising, given its sheer size.”
While the authors of the megalodon zinc isotope study suggest that competition with great white sharks could be have been a factor that drove megalodons to extinction, these species coexisted for millions of years.
“It’s uncertain whether competition can explain the final demise of Otodus megalodon,” says Bazzi. “The data as presented by the authors show that two important species (O. megalodon and the great white shark) coexisted during a period of global environmental change.
“Notably, only the great white shark survived and remains a top predator in open ocean environments today. Determining the cause of extinction of single species can be difficult.”
Campione agrees, noting that competition is everywhere.
“There’s a constant struggle for existence – it’s something that Darwin talked about. So, I do not doubt that megalodon and the great white competed, but whether this led to megalodon’s extinction seems beyond what we can say as palaeontologists,” he says.
“Multiple species can serve similar ecological roles in sympatry. On top of that, the ocean is big. And so, from my view, competition is probably a less important role, and rather changing environments and shifts in oceanic food sources were more likely to be the primary extinction factors..”
Ocean temperature and chemistry were a couple of the environmental changes that occurred around the time megalodon vanished.
“The ocean chemistry and ocean environment changed a lot.” says Campione. “There were major cooling events across the Miocene, including the deposition of glacial sheets at the poles. These were major events that occurred, and together with dealing with the fossil record, it’s so difficult to then extrapolate something that happens on a daily basis to something that we have a record that is plus or minus a few million years.
“Megalodon’s extinction has been attributed to many factors, including their tendency to specialise towards large body size that requires a large amount of food,” says Bazzi. “Its eventual extinction may have ultimately been caused by its inability to adapt to rapid environmental changes and loss of main prey.
“These kind of studies are really valuable. We are always looking for that smoking gun – that one value that will tell us everything we need to know about the biology of these fossil animals. It’s great that more people are exploring different proxies for biology.”
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Qamariya Nasrullah holds a PhD in evolutionary development from Monash University and an Honours degree in palaeontology from Flinders University.
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