Fish evolution

This video from Canada is called Fish evolution in response to climate change.

By Lucas Brouwers in Scientific American:

Heads before Tails: Ancient Fish Evolved Head-First

December 21, 2011

Like most evolutionary tales, this one could have started on the Galapagos Islands. Instead we find ourselves in an ancient sea, near the end of the Devonian, 360 million years ago. A mass extinction has struck life underwater. The armoured placoderms, once an abundant class of fishes, have gone extinct. Other groups of fishes have been decimated and are struggling to survive. But, as a Dutch saying goes, one man’s death is another man’s breath.

Though Lucas Brouwers is Dutch and writes English well, here he makes a mistake. The Dutch proverb says “De een zijn dood is de ander zijn brood”. Dutch “brood” translates into English as bread, not as breath. The saying means that if someone dies, someone else (eg, undertakers, heirs; weapons corporations like BAE or Lockheed during a war) may profit financially from that.

For the ray-finned fishes (fishes whose fins are supported by a ray of spines) this time of trouble is a time of opportunity. With their direct competitors out of the way, they are free to evolve into a multitude of shapes and species, from stream-lined hunters to plump grazers. The fish are dead. Long live the fish!

Fast forward to today. With over 23.000 species alive, ray-finned fishes are the largest and most diverse group of vertebrates of this day. Their rapid evolution after the Devonian mass extinction was the turning point that ensured them their evolutionary success.

Three-quarters of the fish in the sea can trace their origins back to a freshwater ancestor. The finding highlights how important rivers and lakes are as a source of new species, just as that supply is under threat from disappearing freshwater habitats: here.