A gang of cannibal neanderthals butchered and ate 12 of their neighbours in an orgy of violence, according to new research presented to London's Royal Society.
The researchers, who are investigating ancient human remains discovered at the El Sidron cave system in northern Spain, found several bones that had been cracked open to extract the marrow.
The skulls had also been split so the brains and tongues of their human prey could be consumed.
The victims, believed to have been part of a neighbouring tribe, included three children aged between two and nine years old, as well as three teenagers.
Archeologists discovered the remains in 1994, and systematic excavation began in 2000. In total, the remains of 13 individuals were retrieved from the caves, which lie 60ft underground and thus provided ideal conditions for the preservation of the bones.
According to the Sunday Times, lead researcher Carles Lalueza-Fox told the Royal Society that all 12 victims "had been butchered" by the cannibal horde.
"It must have been a big feast. We think neanderthal groups were about 10-12 strong so this may have been a complete family group, although someone may have got away.
"I would guess they were killed in winter when food was short. There is no evidence of any fire so they were eaten raw immediately and every bit of meat was consumed. They even cut around the mandibles of the jaw to extract the tongues."
Laluesa-Fox also claimed the victims were originally slaughtered in a rock shelter above the site where their bones were eventually discovered.
The cannibals stripped the bones of flesh and left them scattered on the floor. A storm eventually washed the bones through an opening into the cave below.