Formicola also noted that the girl had abnormal thigh bones that were bowed and shortened.
The study appears in the June issue of the journal Current Anthropology.
A second multiple burial found at Dolni Vestonice in Moravia, Czech Republic, contained the remains of a disabled teenager thought to have been female.
Lying between two adolescent males, the teenagers had limbs and a skull showing signs of severe deformity, possibly the result of a rare genetic disorder.
Again the bodies appear to have been buried at the same time, Formicola said. They were arranged in an unusual position, with the hands of one male placed on the middle skeleton's pelvic region, which had been covered in red ochre.
The third burial, at Romito Cave in Calabria in southern Italy, revealed the skeleton of a teenage dwarf, believed to be male, entwined in the arms of an adult female. The bodies lay beneath an elaborate engraving of a bull.
Formicola argues that similarities shared by the three multiple burials could be explained by ritual human sacrifice.
The practice hasn't previously been recorded from the Upper Paleolithic period, but is known from other large, hierarchical societies.
(See related: Stone Age Massacre Revealed in British Tombs [March 16, 2007].)
Meanwhile studies of well-preserved remains of Iron Age bodies found in Denmark bogs suggest that the young and disabled were often chosen for human sacrifice.
"Disabled people may have been selected because they were seen as different. These individuals may be feared, hated, or revered," Formicola said.
Was it Homicide?
None of the remains buried at the three Stone Age sites show signs of a violent death.
This could be because the bones no longer show signs of homicide, Formicola said.
Moreover, a sacrifice doesnt necessarily imply injuries to the bones, he added.
Anthropologist David Frayer of the University of Kansas agrees that multiple burials first appeared in Europe during the Upper Paleolithic.
"Something different was going on for sure," he said.
"We always wondered what the odds were of three people dying at the same time at Dolni Vestonice. It's really hard to imagine they died together because all those individuals were fairly young."
But Frayer says he would expect some evidence to show that one or more people in the three graves were killed deliberately.
One of the things that bothers me a bit is that there is no evidence of any homicide, he said. The easiest way to kill somebody is to bash them in the head.
Frayer said there may have just been a greater density of people at that time in history, so it may have been more likely that two or more people would die simultaneously.
Formicola, the study author, accepts that many questions remain unanswered.
But he said the sites stress the complexity of Upper Paleolithic hunter-gatherer societies and the symbolic importance of the burials they left.
"Using information drawn from burials and art we can better [understand] the expressions of the beliefs and rituals left by these populations," he said.
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