A pair of baby skeletons in Alaska are more than 11,500 years old, and offer new hints about the death rituals of early people in North America, researchers said Monday.
The bodies "represent the earliest known human remains from the North American subarctic," said the study in the Proceedings of the National Academy of Sciences, a peer-reviewed US journal.
The infants were found buried 15 inches (40 centimeters) beneath another child's cremated remains, in a circular pit that also held spear points with decorated antler shafts.
An analysis of bones and teeth at the Upward Sun River site in central Alaska revealed that one died shortly after birth and the other was a late-term fetus, researchers from the University of Alaska, Fairbanks and Liverpool John Moores University said.
The infants might have been related, and radiocarbon dating shows they were buried at about the same time as the cremated remains of the three-year-old child above them.
Researchers also found the remains of salmon-like fish and ground squirrels in the burial pit, suggesting that the site was occupied by hunter-gatherers between June and August, when food should have been plentiful.
It is unclear what caused their deaths, but researchers said the discovery of three burials in a group of mobile foragers suggests that food shortages could have been to blame.
"The deaths occurred during the summer, a time period when regional resource abundance and diversity was high and nutritional stress should be low, suggesting higher levels of mortality than may be expected give our current understanding" of survival strategies of the period, the study said.
The burials, found beneath a residential structure, also point to the possibility that people may have stayed in one place longer than previously believed.
Since little is known about death rituals in early humans, and they left behind no written language, researchers must cobble together clues based on what they can observe.
"The presence of hafted points may reflect the importance of hunting implements in the burial ceremony and with the population as whole," the study said.
The hunting weapons were found along with the infant skeletons -- first discovered by archeologists in 2013 -- and might have been added as part of the burial ceremony, researchers said.
"Taken collectively, these burials and cremation reflect complex behaviors related to death among the early inhabitants of North America," said Ben Potter, a researcher at the University of Alaska, Fairbanks.
The study was funded by the US National Science Foundation.