The Jura-Museum, Eischstatt, Germany

Piranhalike teeth and torn fins reveal ancient fish fight

This 150-million-year-old fish (seen as an artist’s illustration) wasn’t named after the piranha for nothing. It apparently used its long, dagger-shaped teeth to slice into other fish, according to a new study, as evinced by the slashed tailfins of some victims found nearby.

Researchers first discovered the animal—christened Piranhamesodon pinnatomus (pinnatomus means “fin cutter”)—in 2016 in the same southern German limestone deposits as the famous feathered dinosaur Archaeopteryx. Most other fish in the shallow sea where P. pinnatomus lived had teeth adapted for crushing, not biting or tearing. (Their stomach contents suggest they ate hard-shelled prey such as clams and sea urchins.)

The scientists think P. pinnatomus might have used “aggressive mimicry” the way modern-day piranhas do—even though they belong to a different branch of the fish family tree. Piranhas today resemble their more peaceable relatives, allowing them to get close enough to unsuspecting prey that they can tear off a fin. (The attack doesn’t kill the prey, and fins can regrow.)

P. pinnatomus, too, resembles other fish found nearby—except for those teeth. The fossil is the oldest bony fish known that would have been able to cut flesh out of larger prey, the team reports today in Current Biology. The researchers say it’s a striking example of evolution inventing some of the same tricks twice.