Saber-toothed anchovy relatives were once fearsome hunters

Their kin now eat mostly plankton. But those long ago had spiky teeth that could spear other fish

Roughly 50 million years ago, some ancient anchovy relatives sported unusual teeth. They had spikes on their lower jaw and a lone upper sabertooth. One such fish called Monosmilus chureloides is caught in the jaws of an early whale as it chases smaller fish in this illustration.

Joschua Knüppe

Ancient relatives of today’s anchovies once had quite the bite. They would have been less like a pizza topping and more of a fearsome predator.

Fossils show that these fish were armed with a mouthful of awesome teeth. Each of two newly analyzed specimens sports a toothy lower jaw and one giant spear jutting down from its top jaw. Stranger still, their single sabertooth sat off-center. Such chompers suggest that the animals hunted other fish.

Hundreds of species of anchovies exist today. Some people find them tasty. But their ancient relatives were very different than the fish people munch on today.

Today’s anchovies feast mostly on tiny organisms called plankton. The modern types “have super tiny teeth. They look nothing like these things,” says Alessio Capobianco. He’s a paleontologist at the University of Michigan in Ann Arbor.

The fossils revealed physical traits that connect these fish with their modern relatives. Today’s anchovies open wide to gulp food. The fossil fish also had a gaping mouth, Capobianco says. “Probably that mouth opening helps to catch fish … because those teeth are so large.”

Even their bodies were large compared to their modern kin. Anchovies today top out at around 37 centimeters (15 inches). Fossils show one of the ancient fish may have stretched nearly a meter (39 inches) long, Capobianco and his team estimate. They shared their findings May 13 in Royal Society Open Science.

The fossils date from roughly 50 million years ago. It was a time known as the Eocene Epoch. It came after the mass extinction that finished off the dinosaurs. The event, roughly 66 million years ago, also wiped out many marine species. Some of the animals that went extinct were large predatory fish. The strange newfound anchovy kin may have evolved to fill those voids. Swimming with them were fish that would look familiar today, notes Capobianco. There were types of tuna, barracudas and mackerels. Also, at that time, “There were sort of failed experiments going on,” Capobianco says. They included “these saber-toothed anchovies that didn’t survive to the modern day.”

As crazy as a T. rex

The authors may be right that the fish were experiments, says Kerin Claeson. She’s a paleoichthyologist (PAY-lee-oh-ik-thee-OLL-uh-gizt). That means she studies ancient fishes. Claeson works at the Philadelphia College of Osteopathic Medicine in Pennsylvania. However, she adds, those authors “can’t rule out … that [the strange anchovy kin] may have lived for a long time, but they just didn’t fossilize very well.”

The scientists used CT scans to peer inside the fossils. That technology uses X-rays to map a sample’s inner structure without tearing it apart. One specimen had been pulled from the ground decades ago, but scientists only now gave it a closer look. The new scans exposed features that weren’t visible from the outside — including the giant teeth.

Having one big fang near the middle of the mouth is pretty unusual, Claeson notes. These animals are an example of the exciting ancient life beyond dinosaurs. These fish “were as crazy as something like a Tyrannosaurus rex … It certainly was a terror just like T. rex was, just swimming around.”

Carolyn Wilke is a former staff writer at Science News for Students. She has a Ph.D. in environmental engineering. Carolyn enjoys writing about chemistry, microbes and the environment. She also loves playing with her cat.

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