Sawfish are about as bizarre as they come. And yet, even these uniquely strange fish have even stranger ancient cousins. Meet Onchopristis, a prehistoric animal whose "face saw" was covered in backward-facing barbs like so many little harpoons.
A not-too-distant relative of the true sawfish alive today, Onchopristis lived during the Cretaceous Period, which ended some 65 million years ago. Like their extant kin, these fearsome fish had long, flat noses (rostrums) lined with "teeth" known as denticles.
Modern sawfish use their rostrums as electric-sensitive antennae during searches for prey, and when food is found, those face swords also come in handy for dispatching it. The normal teeth of Onchopristis (the ones in its mouth, where teeth belong) were sharp, but quite small, indicating that these animals also fed on small fish. It's very possible that they hunted in sawfish-like fashion as well, using their noses to attack, trap and perhaps even sense their prey.
But why the hooked denticles? The obvious answer seems to be that these barbs made stabbing extra effective.
Charlie Underwood of Birkbeck, University of London, notes that the "nose teeth" of Onchopristis don't show evidence of being used against hard substances like sand or bone, suggesting instead that they may have been wielded in defence, for slashing shoals of fish and during combat with rival males.
Because Onchopristis is known mostly from smaller fossil fragments, there's still quite a bit of debate about its overall appearance. An internet search will tell you that these fish reached lengths of eight metres (26 feet), but the truth is more mysterious.
"The size is uncertain as there are only bits," explains Underwood. "But adults reached a minimum of four metres and probably quite a bit larger."
He suggests that fully grown specimens could have measured in at five or even six metres (16 to 21 feet), similar in size to the largest sawfish of today. Based on those estimates, the rostrums of these ancient animals may have been one to two metres (3-6 feet) long.
Exactly what sort of creatures Onchopristis would have defended itself against is also up for debate. You might think an alligator-sized fish with a chainsaw for a face wouldn't have much to worry about, but these animals shared their habitat with sharks, big crocs and even carnivorous dinosaurs.
The famously huge fish-eating Spinosaurus is often depicted going after Onchopristis in exciting predator-prey battles, but Underwood thinks such scenarios might not be totally realistic. "[Spinosaurus] had crocodile-like teeth and so could not cut food and would have largely been limited to fish it could swallow whole," he explains.
Other dinosaurs, however, including the similarly massive Carcharodontosaurus, did have teeth suited for slicing, and may have turned to the water for food on occasion. More likely predators were sharks and crocodiles, which feed on sawfish to this day.
Onchopristis isn't the only fish with this harpoon feature. Other members of its fish family, the sclerorhynchids, are also known to have barbed nose-teeth, including Atlanticopristis from South America and Australopristis from New Zealand. The living sixgill sawshark (also not a true sawfish) sports similar but smaller barbs on its saw-teeth as well.
Though Onchopristis may not yet be famous enough to appear on the big screen, it does make an appearance in the Jurassic World mobile game. Unfortunately, like most creatures in the Jurassic franchise, it's more about spectacle than science – their Onchopristis doesn't even have barbed saw-teeth! The real-life version is way cooler.
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