Fish evolved out of the oceans… huh, what?!Posted: February 10, 2012
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.