UAA researchers’ discovery has important implications for large mammal extinctions

When University of Alaska Anchorage researchers Douglas Veltre, David Yesner and Kristine Crossen, along with Penn State’s Russell Graham began mapping animal remains in a lava tube cave 16 meters (53 feet) below the surface of St. Paul Island, they had no idea that the discovery they were about to make would have very significant implications for both human and environmental theories of Pleistocene megafaunal (large animal) extinction.

Detailed in the paper “Last Outpost of North American Mammoths Found on Isolated Alaskan Island”, which Kris Crossen presented this week at the annual Geological Society of America meeting in Salt Lake City, the woolly mammoth remains found in the cave are reliably dated at about 5,700 years BP (before present).

The researchers suggest in the paper that their work reinforces the theory that human hunting is the main cause of the widespread extinction of megafaunal species worldwide, which occurred concurrently with the rapid growth and spread of human populations in the aftermath of the Last Glacial Maximum. The continued survival of woolly mammoths on uninhabited Bering Sea islands long after the extinction of their mainland cousins adds weight to the theory, according to Veltre, Crossen, Yesner, and Russell.

Qagnax (“Bone” in Aleut) Cave was discovered in 1999 by residents of St. Paul Island, one of five islands comprising the volcanic Pribilof Island group in the eastern Bering Sea. They are the most isolated islands in North America, 500 km (310 miles) off the coast of mainland Alaska, and were uninhabited by humans until the late 18th century when the Russians brought Aleuts there. St. Paul is unique among Bering Sea islands in its lava tube caves, from which animal bones may be collected. Qagnax Cave is a chamber within a lava tube about 15 meters (49 feet) in diameter and 12 meters (39 feet) high connected to the surface by a 4 meter (13 feet) vertical shaft, which made it a perfect natural trap for local animals, including mammoth, polar bear, caribou or reindeer and Arctic fox.

The TDX Corporation, the Aleut village corporation of St. Paul, Alaska, gave permission for fieldwork and analysis, as well as in-kind support for a research project.

The research project began in 2003 and focused on reconstructing the geologic context, photographing and mapping the cave and the faunal remains, collecting the bones, testing the central debris cone, and dating the mammoth remains. The materials were cleaned and dried and are currently housed at the UAA Anthropology Laboratory. Many of the 1,750 bones recovered evidence carnivore/scavenger alteration, including chewed areas and tooth puncture holes. The researchers concluded that the cave acted as a natural trap into which animals fell, some still alive to consume bones and possibly the carcasses of previously trapped individuals.

Tooth dating was done on gelatin derived from the dentine collagen using accelerator mass spectrometry. Two of the teeth and one post cranial bone were subjected to 14C dating. The findings led the researchers to conclude that all of the woolly mammoth bones may have been from a single animal which died about 5,700 years BP. The remains are at least 2,200 years younger than any previously dated mammoth remains from anywhere in North America.

The extended survival of isolated woolly mammoths on the Pribilof Islands may be closely related to the absence of human habitation on the islands until the late 18th century. As the climate began to change with the end of the Last Glacial Maximum, polar and glacial ice melt caused the seas to rise, slowly submerging eastern Beringia and creating a maritime environment on the volcanic islands that remained – the Pribilofs – now isolated from the mainland and humans.

The islands were free of permafrost and enjoyed relatively slight winter snow cover and longer summer growing seasons. The resulting lush coastal vegetation was very similar to that of the Bering Sea islands of today. The abundance of grasses and other vegetation likely contributed to the species’ surviving more than 5,000 years beyond the extinction of mainland mammoths. The waters continued to rise until at least 5,000 years ago, gradually reducing the grazing range available to the large mammals. Active volcanism until about 3,200 years BP possibly contributed to habitat alteration and/ or fragmentation and may have also contributed to the woolly mammoths’ eventual extinction.

Because of their isolation, the authors propose, the Pribilof Islands offer an excellent test case supporting the idea that survival of the mammoths was most likely in areas without human occupation.

A University of Alaska Anchorage Faculty Development Grant provided financial support for Professors Crossen, Veltre and Yesner, and the Denver Museum of Science and Nature provided funding support for Graham.