The discovery of a burial containing 8,000-year-old human skulls, including two that still have pointed wooden stakes through them, has left archaeologists baffled, according to a new study from Sweden.
     During the Stone Age, the grave would have sat at the bottom of a small lake, meaning that the skulls would have been placed underwater. Moreover, of the remains of at least 11 adults placed on top of the grave, only one had a jawbone, the researchers said. The burial did contain other jawbones, although none of them, except for an infant's, were human.
     While excavating the site, archaeologists found various animal bones, said study co-lead researcher Fredrik Hallgren, an archaeologist at the Cultural Heritage Foundation in Västerås, Sweden. "Here, we have an example of a very complex ritual, which is very structured," Hallgren said.
     It was difficult to identify the sex of some of the adults buried at the site, but at least three of the adults were female and six or seven were males, the researchers said. Seven of the adults, including two of the females, showed signs of 'blunt-force trauma' on their skulls, the researchers wrote in the study. But this trauma didn't kill them, at least not immediately, because all of the skulls showed signs of healing, Hallgren said. "This trauma is the result of violence between humans," the researchers wrote, and the men tended to have trauma on top of and on the front of their heads, while the women's injuries were located on the backs of their heads.
     Even more astounding were the wooden stakes found in two of the skulls. One stake had broken, but the other was long, about 1.5 feet (47 cm) in length, and both likely served as handles or mounts for the skulls, Hallgren said. They found a piece of brain tissue inside the skull with the broken stake through it. The fact that the 8,000-year-old brain didn't decompose suggests that the individual was placed in the water soon after death, Hallgren said. However, some of the other skulls may have been placed there long after death, as it's possible the site may have served as a second burial for them, he added.
     This strange burial site would have been hidden from view during the Stone Age, except for a few wooden stakes that may have poked above the water's edge, Hallgren said. Whoever made the grave began by tightly placing large stones and wooden stakes together at the lake's bottom, making a flat structure measuring about 39 feet by 46 feet (12 by 14 m). The bones were placed on top of these stones in a particular order; archaeologists found the human remains in the center of the structure, brown bear bones on the southern part and, finally, big game animals on the southeastern part of the stone packing."It's a very enigmatic structure," Hallgren said. "We really don't understand the reason why they did this and why they put it under water."
     Though mysterious, the underwater burial had an upside: it preserved the remains for posterity. The bottom of the lake was a low-oxygen environment, and limestone in the region's bedrock made the soil more alkaline. Over time, the lake turned into a bog. Eventually, a forest grew over the bog, but the area is still watery.
     "The people who were deposited like this in the lake, they weren't average people," Hallgren said, "but probably people who, after they died, had been selected to be included in this ritual because of who they were, because of things they experienced in life."
     The discovery is "very interesting, but also very perplexing," said Mark Golitko, an assistant professor of anthropology at the University of Notre Dame. "Most of the sites you can look at and get a rough sense of what's going on, but this is one of those where it's, like, I really don't know. It's a very strange site," Golitko said.

Edited from LiveScience (13 February 2018)