Ancient extinctions blamed for lack of fish today
February 08 2012 Lewis Smith
Life may have evolved in the sea but the vast majority of today's fish descended from a freshwater ancestor, researchers say.
Oceans cover 70 per cent of the world’s surface yet they provide a home to as few as 15 per cent of the species, and at best 25 per cent.
A study now suggests that one of the prime reasons for the lack of diversity is that there was a series of mass extinctions in the oceans and the waters had to be re-colonised from freshwater stocks.
Ray-finned fish were chosen for the study because they represent 96 per cent of fish species and can be found in salt and freshwater environments. Researchers established that the split between salt and freshwater today is roughly equal, with 15,149 freshwater species and 14,736 saltwater species, despite freshwater habitats being found in only 2 per cent of the globe.
Moreover, by analysing the ancient family tree researchers from Stony Brook University in the US concluded that today’s ray-finned fish are most likely to have descended from a freshwater ancestor which lived 180 million years ago. This, they said, gave fish in the ocean much less time to diversify.
Dr John Wiens said: “Our results suggest that ancient extinctions in the marine environment may have wiped out the earliest ray-finned fishes living in the oceans, that the oceans were then recolonized from freshwater habitats, and that most marine fish species living today are descended from that recolonization.
“This pattern of ancient extinction and more recent recolonization may help explain why the oceans are now so species-poor, even for fish.
“There are more fish species in freshwater than in saltwater habitats, despite the much greater area and volume of the oceans. More remarkably, our results suggest that most marine fish alive today are descended from freshwater ancestors even though fish and animals in general first evolved in the oceans.”
The findings are published in the journal Proceedings of the Royal Society B.
« Return to the news index
Be the first to comment on this story using the form below