This 2015 video says about itself:
A migration of 10 million anchovies provides an irresistible opportunity for many ocean predators. The swarming, confusing “bait balls” formed by large schools of small and nimble anchovies provide a formidable defense against any one shark hunting alone. However, blacktip sharks have evolved to overcome this challenge.
By Carolyn Wilke, 18 April 2020:
Saber-toothed anchovy relatives hunted in the sea 50 million years ago
Fossils suggest these ancient animals grew up to a meter long and ate other fish
Less pizza topping and more toothy hunter, ancient anchovy kin once had quite the bite.
Fossils show that these fish were armed with a mouthful of fearsome teeth. Each of the two newly analyzed specimens sport spiky teeth along the lower jaw and one giant dagger jutting down from the top jaw. Stranger still, the single sabertooth sits off-center. Such chompers suggest that the now-extinct fish were predators, possibly feeding on other fish, scientists report May 13 in Royal Society Open Science.
Today’s anchovies feast mostly on plankton. “They have super tiny teeth. They look nothing like these things,” says paleontologist Alessio Capobianco of the University of Michigan in Ann Arbor. The ancient fish were also large compared with their modern relatives, which top out at around 37 centimeters. One of the fossil fish may have stretched nearly a meter long, the researchers estimate.
Using CT scans to peer into the fossils, Capobianco and his team discovered shared physical features that tie the ancient fish to their modern kin. Just like today’s anchovies, which open wide to gulp food, these fossil fish had a gaping maw, Capobianco says. “Probably that mouth opening helps to catch fish … because those teeth are so large.”
The fossils, which date from roughly 50 million years ago, are helping fill in a picture of marine life during the Eocene Epoch. At that time, predatory fish like these may have evolved to fill voids left by the massive extinction event that wiped out the dinosaurs along with many marine species about 66 million years ago (SN: 8/2/18).
Fish from groups still around today, such as tuna, barracudas and mackerel, also swam the seas with the anchovies. “There were sort of failed experiments going on at the same time,” Capobianco says, including “these saber-toothed anchovies that didn’t survive to the modern day.”