Five years later, a pair of puppies perfectly preserved in Russia's far northeast region of Yakutia and dating back 12,460 years has mobilised scientists across the world.

"To find a carnivorous mammal intact with skin, fur and internal organs -- this has never happened before in history," said Sergei Fyodorov, head of exhibitions at the Mammoth Museum of the North-Eastern Federal University in the regional capital of Yakutsk.

And the discovery could contribute to the lively scientific debate over the origin of domesticated dogs.

When the hunters stumbled on the first frozen pup in 2011, they alerted Fyodorov who immediately flew out to the remote Arctic tundra, about 4,700 kilometres (2,900 miles) from Moscow and only 130 kilometres from the Laptev Sea, which borders the Arctic Ocean.

Last year he returned for a more thorough look and found the second puppy close to the same spot, farther down the slope. Both had died when they were about three months old.

They most likely come from the same litter, said Fyodorov.

Last week he oversaw the removal of the second puppy's remarkably well-preserved brain -- "the first in the world", he said.

"Puppies are very rare, because they have thin bones and delicate skulls," he said.