The newly discovered extinction event during the Pliocene epoch — 5.3 million to 2.6 million years ago — particularly affected marine mammals, which lost 55 percent of their diversity, the team reported Monday in the journal Nature Ecology & Evolution.
“We were able to show that around a third of marine megafauna (large animals that weigh more than 90 pounds) disappeared about 3 [million] to 2 million years ago,” said lead author Catalina Pimiento, a researcher at the University of Zurich in Switzerland. “Therefore, the marine megafaunal communities that humans inherited were already altered and functioning at a diminished diversity.”
To measure the consequences of the extinction, the team focused on shallow coastal shelf zones — underwater land masses that extend from a continent, forming areas of relatively shallow water — examining the effects that losing a range of native species had on coastal ecosystems. The team focused on functional entities, which are groups of animals that are not necessarily related, but function similarly within ecosystems.
The team found that seven functional entities were lost in coastal waters during the Pliocene, which was enough to erode functional diversity. About 17 percent of the total diversity of ecological functions in the ecosystem disappeared and 21 percent changed. Previously common predators disappeared, while new competitors emerged, which forced marine animals to adjust. These changes to marine populations occurred as coastal habitats were significantly reduced by dramatic sea level shifts.
As much as 43 percent of sea turtle species were lost, in addition to 35 percent of seabirds and 9 percent of sharks. While several new forms of life developed in the succeeding Pleistocene epoch — about 2.6 million to 11,700 years ago — previous levels of diversity could not be reached again.
The team believes the sudden loss of productive coastal habitats, combined with ocean-based factors such as altered sea currents, primarily influenced these extinctions.
“Our models have demonstrated that warm-blooded animals, in particular, were more likely to become extinct. For example, species of sea cows and baleen whales, as well as the giant shark Carcharocles megalodon disappeared,” Pimiento said.
The team connected their findings from the extinction event to modern conditions, in which large marine species such as whales and seals are highly vulnerable to human influences.
“This study shows that marine megafauna were far more vulnerable to global environmental changes in the recent geological past than had previously been assumed,” Pimiento said.
(Photos by National Oceanic and Atmospheric Administration.)