the biggest fish species decided to hunt more and more food after a good boom of life. our already most powerful species became more dependent on its environment and developed small teeth, making it one of the first toothed fish on the planet. it has a very blunt jaw and backwards-facing teeth with a large throat, topped off with a much smaller, sharper fin for better aerodynamics. it happens to try to swallow its prey rather than slicing it, similar to things like the goblin shark, despite having a very short neck. it also evolved some environmental stealth shading to become an ambush predator.
it grew to about 6 feet long and preys on smaller fish and occasionally the squids. maybe its large tail will be used for something useful further down in its evolutionary branch...
