Huge Saber-Toothed Anchovies Emerged After Dinosaurs Went Extinct in 'Failed Evolutionary Experiment'

In the aftermath of the mass extinction that killed off the dinosaurs, huge saber-toothed anchovies emerged, scientists have now discovered. The largest species discovered is estimated to have been around 3.2 feet long, or roughly ten times the length of anchovies living today. They have been dubbed "failed evolutionary experiments" that appeared in the aftermath of the disappearance of large predatory fish around 66 million years ago.

The end-Cretaceous mass extinction even saw around 75 percent of all species on Earth disappear. The loss of large predatory species left vacancies in ecosystems for new species to come and fill. It is thought the newly discovered species of fish were among the lineages that attempted to exploit these gaps by diversifying and evolving new adaptations, Alessio Capobianco, from the University of Michigan, told Newsweek in an email.

Capobianco is lead author of a study describing the newly discovered species' of fish. The oldest fossil of saber-toothed anchovies dates to 54 million years ago, while the latest they found was 45 million years old, indicating they existed for at least nine million years. The team's findings and published in Royal Society Open Science.

In the study, they say the fossils analyzed represent a new clade of large-bodied clupeiform fish—an order that includes anchovies and herrings. These new species are characterized with a single row of fang-like teeth on the lower jaw, with none on the upper jaw other than a single, giant fang. Capobianco said jaws like this are "completely unique and unprecedented in any other fish."

He added that the sabertooth is slightly offset from the middle, giving the fish a slightly asymmetric appearance, and making them even more unusual.

The team studied two species. The largest one, Monosmilus chureloides, could reach 3.2 feet in length and its sabertooth was approximately one inch long—about 30 percent of the length of its skull.

giant saber-toothed anchovy
Artist impression of Monosmilus chureloides, a saber-toothed anchovy that lived 45 million years ago. Joschua Knüppe

Explaining why these huge saber-toothed anchovies may have emerged, Capobianco said this point in history was when most major lineages of predatory fish evolved. These include tuna, barracudas and mackerels.

"The discovery of saber-toothed anchovies shows us that, alongside these successful evolutionary stories that persist to the modern day, other lineages also evolved remarkable specializations to occupy the ecological role of predators, but they were ultimately unsuccessful," he said. "Viewed in this context, organisms like the saber-toothed anchovies can be called 'failed evolutionary experiments'—short-lived groups that did not survive to the modern day with remarkable ecologies that cannot be predicted on the basis of living species."

The team does not know what the sabertooth was used for. They are clearly the teeth of a predator," Capobianco said. "Living species with large fangs use them in different ways: some of them use the fangs to stab or impale their prey, some use them to make their mouth a sort of 'cage' or 'trap' for smaller fishes. For the saber-toothed anchovies, this is purely the realm of speculation for now, as there are no good modern analogues with a comparable set of teeth."

Why these species were ultimately unsuccessful is unknown. One suggestion is competition with other predatory fish drove them to extinction. Climate change around 40 million years ago may also have played a role, but we know too little about these extinct fishes to really say anything at this point," Capobianco said.

The research also opens questions about what the ancestors of modern anchovies were like. Existing species are small, plankton-feeding creatures with tiny or no teeth. "Were the anchovies' ancestors also fanged, fish-eating creatures, and only later they evolved adaptations for plankton feeding? Or were they similar in habits to the living species, and the saber-toothed forms evolved from plankton eaters? Both these hypotheses are possible, and we would need more research and more fossils to be able to answer this," Capobianco said.