Fish evolved out of the oceans… huh, what?!

There has already been, since the late 1970s, much work done to show that whales and dolphins, collectively called cetaceans, evolved from exclusively land-dwelling mammals. Now it appears there is a case to be made that most of the fish we see in oceans today actually arose from freshwater ancestors.

96% of all fish on Earth are in the group called ray-fins. Research summarised by New Scientist shows that 75% of ray-fins share a heritage that arose in freshwater environments. They moved into pelagic habitats perhaps 170 million years ago.

So what happened to the organisms that never left the oceans? Mass extinctions, probably – for instance 95% of marine organisms were extinguished in the Permian-Triassic’s Great Dying – with freshwater habitats somewhat protected from disaster.

Via io9

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