Two decorated bones might have been crafted by the enigmatic ancient humans known as Denisovans, who interbred with early modern humans tens of thousands of years ago.

Francesco d’Errico at the University of Bordeaux in France and his colleagues studied two fragments of animal rib found at a site in China known to have been used by ancient hominins. The ribs came from unknown large mammals and are 105,000–125,000 years old.

After the bones had aged, a sharp tool was used to carve them with roughly parallel lines. One bone is flecked with ochre, a coloured mineral often used by early modern humans.

According to the authors, neither butchery nor modern handling could account for the lines. The researchers also say that Denisovans — who are known mainly from their DNA — were probably the hominins using the site when the bones were marked. The team argues that the deliberately incised bones suggest that Denisovans were capable of using symbols.