Unlike living coelacanths, which are slow-moving fish with peculiar broad tails, the extinct ancestor had a tuna-like forked tail and was probably a fast-moving, shark-like predator, Canadian researchers from the University of Alberta report in the Journal of Vertebrate Paleontology.
The 3-foot long fish with a massive symmetrical forked tail quite unlike the tails of any other living or fossil coelacanths has been named Rebellatrix, the "rebel coelacanth.
The fossils were discovered on rocky slopes in Wapiti Lake Provincial Park in British Columbia.
Both the shape and the stiffness of the tail fin are unique amongst coelacanths, researchers said.
Because similar tail fins occur today in fast swimming predatory fishes such as tuna or barracuda, Rebellatrix was probably an active predator capable of fast bursts of swimming to catch other fishes living in ancient seas.
The unusual tail evolution may have been a specific response following the Earth's greatest mass-extinction event at the end of the Permian, 250 million years ago, as coelacanths evolved to fill a vacant niche unoccupied by other predatory fishes, scientists said.
"This is an amazing discovery which overturns the age old image of coelacanths as slow moving fishes and shows the resilience of the group to come back in true fighting form after surviving the world's most devastating mass extinction event," said John Long of the Natural History Museum of Los Angeles County, an expert in fossil fishes who was not involved in the study.