In 1991, a Norwegian geologist found one ancient polar bear bone. 34 years later, 6,000 bones revealed a 75,000-year-old Arctic community

In 1991, geologist Stein-Erik Lauritzen discovered a polar bear rib inside a cave near Kjøpsvik in northern Norway. What looked like a single ancient bone eventually led researchers to a much larger discovery.

More than three decades later, researchers examined over 6,000 bone fragments from the cave system, combining traditional identification with ancient DNA and several dating methods. The results revealed evidence of a diverse Arctic animal community that existed during a relatively mild period of the last glacial era, as per a Science Blog report.

The findings, published in PNAS in 2025, included polar bears, walruses, bowhead whales, reindeer, seabirds, freshwater fish, and a collared lemming not previously recorded in Scandinavia.

One bone opened the investigation

Lauritzen found the polar bear rib on August 8, 1991, in Arne Qvamgrotta, a branch of the Storsteinhola cave system.

The cave lies at about 68.1 degrees north, just inside the Arctic Circle. Limestone mining and tunnel work had exposed the deposit, allowing the ancient remains to be discovered.

Initial work dated the rib to at least 70,000 years ago. Researchers later returned for larger excavations, with major field seasons taking place in 2021 and 2022.

DNA helped identify what the bones could not

The remains were highly fragmented, making many of them difficult to identify from their shape alone.

Traditional osteological analysis could assign only about 5.7% of the fragments to a family or more precise group, as per the Science Blog report. Researchers therefore turned to bulk-bone metabarcoding, extracting short DNA sequences from groups of fragments and comparing them with genetic reference libraries.

Together, the two approaches identified 46 vertebrate taxa from 30 families. The collection included 23 birds, 13 mammals and 10 fish.

The remains point to a changing coastal landscape

The species represented several parts of the surrounding environment.

Polar bears, ringed seals, bearded seals, walruses and bowhead whales pointed to sea ice. Blue whales and harbour porpoises represented open-water environments.

Atlantic cod, haddock and golden redfish showed the presence of cold marine waters, while Arctic grayling and other freshwater fish indicated nearby freshwater habitats.

On land, the researchers identified Arctic foxes, reindeer, hares, tundra voles and the collared lemming.

Together, the remains suggest Arctic or subarctic tundra alongside seasonal or perennial sea ice, freshwater and at least some pine.

The community dates to a relatively mild glacial period

The main assemblage was placed within Marine Isotope Stage 5a, most likely between about 85,000 and 71,000 years ago.

This period, known as the Odderade interstadial, was a relatively mild phase within the Weichselian glacial period.

The researchers did not assign every bone an exact age of 75,000 years. Instead, they combined radiocarbon limits, optically stimulated luminescence, uranium-thorium dating, cosmogenic burial dating and estimates based on evolutionary relationships.

The remains were also concentrated within a stratified sedimentary unit. The researchers treated them as evidence of one ecological interval while acknowledging that the material could have accumulated over thousands of years.

A collared lemming revealed a lost Scandinavian population

One of the most notable findings was a collared lemming, Dicrostonyx torquatus.

The fossil provides the first evidence that the species once reached Scandinavia. It is now absent from Fennoscandia, although collared lemmings still live farther east, including in Russia.

The specimen belonged to a mitochondrial lineage with no living descendants. Similar extinct mitochondrial lineages were also identified in the polar bear and Arctic fox material.

The findings show that the presence of a species today does not necessarily mean that ancient populations or genetic lineages survived unchanged.

The cave was not necessarily home to all the animals

The remains do not indicate that all of the animals lived inside the cave.

Researchers found no burning, cut marks or other evidence of human accumulation. Predators may have carried some prey into the cave, while marine mammal remains may have come from scavenged carcasses.

Some marine species were identified only through DNA, possibly because their lipid-rich bones preserve poorly and had become too fragmented for traditional identification.

The cave therefore provides an ecological record rather than evidence of a single group of animals gathered there at the same time.

A vanished Arctic ecosystem

The researchers' findings suggest that the northern Norwegian coast once supported a combination of habitats that included tundra, freshwater and sea ice, as per the Science Blog report.

When colder and more heavily glaciated conditions returned, the region apparently stopped serving as a refuge for these populations. Some species later returned from elsewhere, while others no longer occur in the area.

The extinct mitochondrial lineages provide evidence of that turnover.

What began with a single polar bear rib eventually revealed a much broader story about how animals lived along the Arctic coast during a warmer interval of the last glacial period and how those populations changed as the climate shifted.