A prehistoric bone might be the missing link between humans and fish.
Scientists say they have found a 365-million-year-old arm bone, the oldest ever. It's the earliest link between fins on a fish and legs on an animal.
The way fish evolved legs has always been a bit of a mystery, and this new bone provides a valuable clue.
The bone, found by a road building site in the USA, is thought to have given fish the ability to do a kind of 'push-up", lifting them off the ground.
Nothing like this before
The bone was found in 1993, but no-one realised how important it was until recently because it was encased in sandstone.
Dr Michael Coates, from the University of Chicago, said: "We had never seen one like it before."