Boris was a cave lion cub that lived some 44,000 years ago and was aged between two to three weeks when he died.
It is possible his death was a result of a den cave collapsed, visible traces of internal injuries which could have been caused by rock fall were in evidence.
Naturally preserved in the Siberian permafrost.
Boris had a severed tail. This led to speculation he was an ancient lynx not a cave lion. Scientists were worried by the lack of a tail on Boris, but the excavation of the body from the permafrost cost the body its tail. Tests concluded the body was definitively a cave lion cub. Boris is the largest cub found in Yakutia.
The bones, brain and other organs are all preserved.
He was dated to about 44,000 years ago. He was plump and well fed at the time of his death. Another lion cub mummy, Spartak, was later found in the same den some 15 metres away, but was dated to 26,000 years ago - she lived 18,000 years after Boris.