An extinction event involving one-third of marine megafauna in the oceans occurred before the ice age, according to a new study published in Nature Ecology & Evolution.
When investigating marine megafauna fossils from the Pliocene and Pleistocene epochs, researchers discovered that about a third of marine megafauna had disappeared about two to three million years ago.
“Therefore, the marine meta-faunal communities that humans inherited were already altered and functioning at a diminished diversity,” said lead author Dr Catalina Pimiento, who conducted the study at the University of Zurich's Paleontological Institute and Museum.
The loss covered as much as 55 percent of the diversity of marine life. This included 43 percent of sea turtle species, 35 percent of sea birds and 9 percent of sharks.
Although the subsequent Pleistocene epoch saw the emergence of a number of new species – including the polar bear Ursus, the storm petrel Oceanodroma or the penguin Megadyptes – this could not reach earlier levels of diversity.
As a result of this extinction event, seven functional entities were lost in the coastal waters during the Pliocene. (Functional entities are groups of animals that are not necessarily related, but they share similar characteristics in terms of the function they play on ecosystems.)
This resulted in the emergence of new competitors, the loss of predators and adaption to the new circumstances became necessary. Violent sea levels caused the reduction of coastal habitats.
Dr Pimiento said, “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 This study shows that marine megafauna were far more vulnerable to global environmental changes in the recent geological past than had previously been assumed.”