For an estimated 20 million years, a shark three times the size of the modern great white hunted marine life off the coasts of the Pacific, Atlantic, and Indian oceans. Called megalodon (Carcharocles megalodon), the species was likely one of history's most terrifying apex predators, with a bite more powerful than a T. rex and a weight greater than that of 10 adult elephants.

Some 2.5 million years ago, megalodon's vicious reign of terror against whales, large sea turtles, and anything else smaller than itself suddenly came to an end. According to a new study published in the journal Nature Ecology & Evolution, the massive shark fell victim to a previously unknown global extinction event that also killed off around a third of marine megafauna.

"This extinction took place in both coastal and oceanic species,” Dr. Catalina Pimiento, who led a team from the University of Zurich in the study of megafauna marine fossils from the Pliocene and Pleistocene epochs, told Newsweek. “We just focused on coastal species to assess the effects of the extinction on functional diversity, and to evaluate if the loss of coastal areas played a role."

The term "functional diversity" describes groups of animals that are not necessarily related but play similar roles in ecosystems. According to Pimiento, her team discovered a loss of seven functional entities in coastal waters during the transition from the Pliocene to the Pleistocene. Those species that went extinct consequently caused a chain reaction that led to a steep dropoff in marine diversity.

"Above all, the newly discovered extinction event affected marine mammals, which lost 55 percent of their diversity," the team shared. "As many as 43 percent of sea turtle species were lost, along with 35 percent of sea birds and 9 percent of sharks."

As for the cause behind this extinction event, the researchers believe sharp fluctuations in sea levels, likely due to increased glacial oscillations near the end of the Pliocene, negatively impacted critical coastal habitats. The formation of the Panama Isthmus some 3 million years ago between North and South America, effectively cutting off the Atlantic from the Pacific, also drastically changed ocean currents.

Drastic sea level fluctuations during the transition from the Pliocene and into the Pleistocene, shown in the middle of the graph, likely played a role in wiping out one-third of marine megafauna. Drastic sea level fluctuations during the transition from the Pliocene and into the Pleistocene, shown in the middle of the graph, likely played a role in wiping out one-third of marine megafauna. (Photo: Root Routledge)

These dramatic swings in climate had the largest impact on warm-blooded marine animals like megalodon.

"Our models have demonstrated that warm-blooded animals in particular were more likely to become extinct," Pimiento said in a statement. "For example, species of sea cows and baleen whales, as well as the giant shark C. megalodon, disappeared. This study shows that marine megafauna were far more vulnerable to global environmental changes in the recent geological past than had previously been assumed."

The researchers plan to use the insights gained from the study to better gauge the health of modern day megafauna that also face a rapidly changing environment from man-made climate change. Megalodon may no longer exist, but care should be taken to preserve its decedents and the food chain that supports them.

"Our study cautions that as anthropogenic climate change accelerates and triggers regime shifts in coastal ecosystems the potential consequences for marine megafauna should not be underestimated," they conclude.

Michael d'Estries ( @michaeldestries ) covers science, technology, art, and the beautiful, unusual corners of our incredible world.