A previously unknown mass extinction may have killed up to a third of large marine animals 2-3 million years ago, according to an international team of paleontologists.

The team, led by Dr. Catalina Pimiento of the Leibniz Institute for Evolution and Biodiversity Science and the Paleontological Institute and Museum at the University of Zurich, analyzed fossilized remains of marine megafauna from Pliocene and Pleistocene epochs (5.3 million to around 9,700 years ago).

“We were able to show that around a third of marine megafauna disappeared about three to two million years ago,” Dr. Pimiento said.

“Therefore, the marine megafaunal communities that humans inherited were already altered and functioning at a diminished diversity.”

“The newly discovered extinction event affected marine mammals, which lost 55% of their diversity. As many as 43% of sea turtle species were lost, along with 35% of sea birds and 9% of sharks,” the researchers said.

“On the other hand, around a quarter of animal species, including the polar bear Ursus, the storm petrel Oceanodroma or the penguin Megadyptes, had not existed during the Pliocene. Overall, however, earlier levels of diversity could not be reached again.”

In order to determine the consequences of this extinction, Dr. Pimiento and co-authors concentrated on shallow coastal shelf zones, analyzing the effects that the loss of entire functional entities had on coastal ecosystems.

“Functional entities are groups of animals not necessarily related, but that share similar characteristics in terms of the function they play on ecosystems. The finding: seven functional entities were lost in coastal waters during the Pliocene,” they said.

“Even though the loss of seven functional entities, and one third of the species is relatively modest, this led to an important erosion of functional diversity: 17% of the total diversity of ecological functions in the ecosystem disappeared and 21% changed.”

“Previously common predators vanished, while new competitors emerged and marine animals were forced to adjust.”

“In addition, we found that at the time of the extinction, coastal habitats were significantly reduced due to violent sea levels fluctuations.”

The team proposes that the sudden loss of the productive coastal habitats, together with oceanographic factors such as altered sea currents, greatly contributed to these extinctions.

“Our models demonstrate 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,” Dr. Pimiento said.

“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 research was published online this week in the journal Nature Ecology & Evolution.

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Catalina Pimiento et al. The Pliocene marine megafauna extinction and its impact on functional diversity. Nature Ecology & Evolution, published online June 26, 2017; doi: 10.1038/s41559-017-0223-6