引用元：エデスタス – Wikipedia https://ja.wikipedia.org/wiki/%E3%82%A8%E3%83%87%E3%82%B9%E3%82%BF%E3%82%B9
Given that our species is over 306 million years too late to observe Edestus in action, there’s been plenty of debate about how this ancient fish employed its wicked grin. The most obvious answer – that Edestus snipped prey with scissor jaws – doesn’t work. (This has been a recurring problem in paleontology – just because a structure looks like a human-invented tool, it doesn’t mean the structure was used the same way.) The tooth whorls of Edestus curved away from each other along their length, so much so in the early species Edestus newtoni that the fish must have looked perpetually puckered to give a serrated kiss. Only a few teeth at the very back of the row would actually slide past each other to shear through shell or scale.
With the scissor hypothesis in doubt, paleontologists espoused a variety of speculative functions. University of Colorado paleontologist Wayne Itano ran down the list in a 2014 paper on Edestus. Perhaps Edestus trawled for jellyfish, burrowed in the mud after clams, or scraped shellfish off their moorings. Or maybe Edestus snagged prey with its upper jaw and sawed through it with the lower, working its fishy chin back and forth to cut victims into manageable chunks.
All these ideas are easily-imagined, but they’re also without supporting evidence. A better contender, proposed by John Long and elaborated on by Itano, is that Edestus subdued prey with a bit of prehistoric headbanging.
引用元：Fossil Fish Sliced Prey With Bizarre Jaws https://www.nationalgeographic.com/science/phenomena/2015/04/09/fossil-fish-sliced-prey-with-bizarre-jaws/