Some two million years ago, a third of the largest marine mammals went through a dramatic event that saw them being wiped out by an unknown event. This not only dramatically affected all marine biodiversity, but seemed to change the way entire ecosystems functioned.
A team of scientists analyzed fossils of marine megafauna from the Pliocene and the Pleistocene epochs (5.3 million to around 9,700 years BC). While marine mammals were the most threatened, they weren't the only ones. Extrapolating from the data, they concluded that a whopping 43% of all turtle species were lost, as well as 9% of shark species. Some 35% of birds also went extinct. All in all, marine mammals lost 55% of their diversity, never to recover it again, and this cascaded into other species in the ecosystem.
“We were able to show that around a third of marine megafauna disappeared about three to two million years ago. Therefore, the marine megafaunal communities that humans inherited were already altered and functioning at a diminished diversity”, explains lead author Dr. Catalina Pimiento, who conducted the study at the Paleontological Institute and Museum of the University of Zurich.
This wasn't without consequence, and the entire ecosystem struggled to recover. Pimiento estimates that 17 percent of the total diversity of ecological functions in the ecosystem disappeared and 21 percent changed. Left without their preferred food source, common predators couldn't adapt and went extinct, while new species emerged, challenging the older ones.
It's not clear what triggered this extinction, but because large marine mammals were especially affected, researchers believe it was a climate change. Since this extinction wasn't even known before, more research is needed before the cause can be identified with certainty.
“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”, explains Dr. Pimiento. “This study shows that marine megafauna were far more vulnerable to global environmental changes in the recent geological past than had previously been assumed”.
This draws significant similarities to today's situation. Nowadays, climate is warming once again, but at a much faster rate than it did at any point in at least a few million years -- because the cause isn't natural, it's anthropic. It's us. Marine mammals such as dolphins and whales are once again under great threat due to climate change, and it's quite possible that we're once again headed for a great extinction.
Journal Reference: Catalina Pimiento, John N. Griffin, Christopher F. Clements, Daniele Silvestro, Sara Varela, Mark D. Uhen and Carlos Jaramillo. The Pliocene marine megafauna extinction and its impact on functional diversity. June 26, 2017. Nature Ecology & Evolution. DOI: 10.1038/s41559-017-0223-6.