A 22-year-old fantasy story has earned its author an advance of $5m (£2.8m), the highest amount paid for a debut British children's book.
Paver was an established author of love stories when she wrote the book
Author Michelle Paver re-wrote Wolf Brother as a children's book following the success of the Harry Potter series.
Published in the UK on Thursday, the book rights have also been sold to the US, Japan, France and Iceland.
Agent Peter Cox said: "Wolf Brother is very, very tough and gritty. It's been described as Mad Max for children."
Paver, who lives in London and previously worked as a lawyer, began writing the book while studying biochemistry at Oxford University.
By last year she was an established author of love stories when she turned the work-in-progress into a children's novel.
"I was leafing through it and the light bulb switched on above my head that
it should be set further back in the Stone Age," she said.
"That was an era that I was passionate about and because the central
character was a 12-year-old boy it made sense to make it a children's book."
Wolf Brother features Torak, a 12-year-old hunter who lives in a forest. After his father is killed he teams up with an orphaned wolf cub and sets out to rid the forest of an evil force.
Paver researched the book by staying with nomadic tribesmen in Finland, Lapland and Greenland.
Sir Ian McKellen has recorded an audio version of Wolf Brother
"I want the reader to smell and taste the forest and I cannot do that if I haven't experienced it myself," she said.
The book will now form the first in a six-part series called The Chronicles of Ancient
An audio version of Wolf Brother has been recorded by Lord of the Rings actor Sir Ian McKellen.