A tenderly decorated grave discovered in Alaska holds the remains of two infants dating back 11,500 years, the youngest Ice Age humans yet found in the Western Hemisphere, archaeologists say.

Interred together inside an ancient residence, one child was about 12 weeks old at the time of death, the other, a late-term fetus — the first known instance of a prenatal burial in the Americas.

Researchers say that the babies were memorialized with an array of goods that was, by Paleoindian standards, rather lavish.

The grave was ornamented with a coating of red ochre and a complement of hunting tools, including two large stone points and four long foreshafts fashioned out of carved elk antler.

The hunting tools, known as hafted bifaces, are the earliest examples of their kind found in North America.

Together, the remains and artifacts, all found within an Ice Age residence, provide unprecedented insights into the nature of life and the rituals of death among some of the continent’s earliest inhabitants, researchers say.

“This mortuary treatment is the first of its kind in the New World — no other Paleoindian burials share this feature,” said Dr. Ben Potter of the University of Alaska Fairbanks, referring to the burials being found inside a residence.

Potter and his team found the grave last year at a site known as Upward Sun River in central Alaska, while investigating a structure that appears to have been a seasonal fishing, hunting and foraging camp.

And they discovered the grave directly beneath a similarly grim feature that the team found in 2010: the cremated remains of a 3-year-old boy. [Find out what we learned from an even older child burial in Montana: “Genome of America’s Only Clovis Skeleton Reveals Origins of Native Americans“]

Why one body was cremated while the other two were not is one of the many mysteries posed by the find, Potter said.

The discrepancy could relate to the ages of the dead, or to their sex, as the two infants appear to have been female, and possibly twins.

“This is the first evidence of multiple individuals [buried] within a single feature with fundamentally different treatments, which may reflect situational factors, [such as] who was present or absent at each event, or the expectedness or unexpectedness of the deaths, or age-grade differences,” he said.

However, the burials did not occur very far apart in time.

“It is most likely that all three children are part of a single community that used this exact feature,” Potter said of the structure.

“Since this appears to be a summer residential base camp, it is plausible that both burial events occurred during the same summer or during subsequent summers,” he said.

The stratigraphy, or layering of soils, around the remains is the clearest indicator of this, suggesting a rather rapid series of somber events, Potter explained.

The infants were buried first, their grave having been dug under the camp’s main cooking hearth. They were then covered with the hearth’s original contents — soil, charcoal, and animal bones, mostly fragments from salmon and ground squirrels.

But with the subsequent death of the toddler, anywhere from a few weeks to a full year later, the boy’s remains were cremated in the hearth itself, and the site was abandoned.

Though bleak, these events produced an array of artifacts and other clues that offer tantalizing glimpses into the lifeways of ancient Alaskans, beginning with the hunting tools that were buried with the infants.

“The grave goods give us a rare window into ideology or belief systems of these ancient peoples,” Potter said.

“There is a clear importance ascribed to hunting implements, and they may reflect the importance of terrestrial hunting within the culture.”

The four antler shafts are “significantly longer” than others known from this era in North America, averaging about a half-meter in length, and Potter noted that they are similar in size to shafts found in eastern Siberia.

Three of the foreshafts were also carved with multiple X patterns, a design that’s “unprecedented” in North American hunting tools, he and his team say.

But the most significant aspect of the tools may simply be that all of their components were found together, in a setting dated farther back than any others yet found.

“The stone points and antler foreshafts were clearly hafted, giving us the oldest glimpse into functions of this compound technology,” he said.

“Most points or rods are found in isolation, and many hypothetical functions have been ascribed to the organic components.” [Read about a related find: “13,500-Year-Old Tool-Making Site Uncovered in Idaho Forest“]

Even the contents of the hearth, which separated the burials, retain clues to Paleoindian life, Potter said.

“The presence of salmon before the earlier burial and before the later burial indicate multiple episodes of salmon fishing, providing evidence for broader diets than just big-game for this early period,” he noted.

And indeed, simple survival in ancient Alaska — even during the relative time of plenty in the summer months — may have been far harder than experts have thought, as the children’s graves attest.

“While we caution that the sample size is small, the evidence of deaths of three very young individuals at a time of year when we expect the least amount of resource stress — that is, the highest abundance of resources — may indicate that nutritional stress was higher than our models indicate,” Potter said.

“The significance of the site is multifaceted,” he added.

Future research may provide more details about the very short life-stories of those buried at Upward Sun River.

But the site also holds a potential trove of information about the children’s community, its history, and its genetic and cultural influences on the people of Ice Age North America. [Who were the first Americans? “Ancient Feces From Oregon Cave Aren’t Human, Study Says, Adding to Debate on First Americans“]

“The potential for ongoing and future studies on ancient DNA and stable isotopes will provide a wealth of direct data on genetic affiliation with modern populations and ancient samples, [as well as on the] paleodiet of the [children’s] mother(s) and mobility,” Potter said.

He and his colleagues report their findings in the Proceedings of the National Academy of Sciences.

Potter BA, Irish JD, Reuther JD, & McKinney HJ (2014). New insights into Eastern Beringian mortuary behavior: A terminal Pleistocene double infant burial at Upward Sun River. Proceedings of the National Academy of Sciences of the United States of America PMID: 25385599