Scientists have used a fish fossil to find out what an ancient fish looks like... and it has really weird teeth!
It's called a Helicoprion and it lived 270 million years ago.
Until now, scientists knew the fish had some sort of spiral-shaped teeth, but they weren't sure how they worked.
Using special scanners and computer images, they say they've now solved the mystery.
The scientists found that the spiral was connected to the fish's lower jaw, in the back of the mouth.
Teeth instead of a tongue
Dr Tapanila, one of the researchers, said: "Imagine that... instead of having a tongue, you have this large spiral of teeth."
He explained that when the fish catches food it closes its mouth and the teeth spin backwards.
This helps the fish eat its prey which is thought to be squid.
The Helicoprion may have been bigger than a man too, as the scientists say the fossil could also show they were more than seven metres long.