A Stone Age ring made of deer antler was discovered at a Neolithic site in Denmark that has been hidden for millennia, having been swallowed by the sea thousands of years ago.

The find, described as "unique," was discovered at an archaeological site in Lolland, Denmark's fourth-largest island, amid several other objects forged from organic material like wood and bone—including a T-shaped antler ax.

The ring is broken but "otherwise perfectly preserved," say researchers writing in Royal Society Open Science.

The object is 2.4 centimeters (0.95 inches) in diameter, making it large enough to fit a man's finger. It is finely polished and contains only "microscopic" scratches, while the inside still displays traces of the original carving. Its relatively pristine condition suggests it was barely worn or had been broken in the manufacturing process, researchers say.

The study's authors were not able to date the object directly and instead based the age of the ring on objects located nearby. However, tests on artifacts found near the ring suggest it was made 5,500 to 6,300 years ago, during the Early Neolithic period (3900-1700 BCE).

Further testing identified the material—the bone of an elk (Alces alces) or red deer (Cervus elapse)—and suggested it came from the antler. The researchers noted some ambiguity, saying that it is not always possible to differentiate between the material of two such closely related species.

Yet they say it is likely red deer, the more local of the two species. Elk vanished from the area in response to rising sea levels and that would suggest the ring (or the antler it was made from) had been imported.

The proliferation of rings made of bone and other osseous material (like antler) began in the Anatolian Neolithic in what is now the Middle East. It expanded, gaining popularity in southern and central Europe. However, according to the study's authors, the ring discovered at Syltholm is only the second that has been found and can be traced to the Early Neolithic in Denmark.

It is not known why this type of jewelry is so uncommon in Denmark. One suggestion is that it is a matter of preservation and objects of this kind have not survived.

"Reasons may simply be due to preservation, or their small size," lead author Theis Jensen, a postdoc at the University of Copenhagen, told Newsweek. "It could also be that they are rare imports from the Neolithic societies in northern Germany."

The first ring was discovered at a site near Jutland in central Denmark and is "considerably smaller," suggesting it belonged to a woman or child. A second thing differentiating it from the one found at Syltholm is its material. Testing suggests it was made of wild boar tusk.

The researchers put forward the idea that there may have been two separate ring manufacturing processes—one that involved antlers or bones and was favored in the east and one that involved tusks and favored in the west.

Archaeologists believe the 6,000-year-old ring was made from red deer antler.Tim Graham/Getty

In December, researchers announced another find at Syltholm—a 5,700-year-old birch pitch (described as Neolithic "chewing gum") containing human DNA. In a world-first, scientists were able to extract an entire human genome from something other than human bone.

"Culturally the site is very interesting as it captures the transition from the Mesolithic to the Neolithic, and it seems that the people living there, were both culturally and genetically still hunter-gatherers, even though they lived in the Neolithic," said Jenson. "What we don't know is if this transition was associated with cultural integration or if this was a conflict or displacement story."

The was found broken in two but otherwise perfectly preserved. University of Copenhagen/ Theis Jensen