The mummified remains of a 14,000-year-old wolf cub, discovered in Siberian permafrost, have provided researchers with genetic material from a woolly rhinoceros, offering new insights into the species' rapid extinction. Analysis of the rhinoceros DNA, retrieved from the cub's stomach contents, suggests that climate warming, rather than human hunting, played a primary role in the disappearance of woolly rhinos at the end of the last ice age.
Discovery of the Ancient Wolf Cubs
In 2011, a two-month-old female wolf cub was discovered mummified in Siberian permafrost near Tumat village. Researchers estimate the cub died approximately 14,400 years ago when a landslide caused its underground den to collapse. A second wolf cub, believed to be its sister, was located at the same site in 2015. Autopsies on both cubs indicated no signs of injury, supporting the theory of a sudden death due to the den collapse. Tests on the cubs also suggested they had begun consuming solid food while still receiving milk from their mother.
Genetic Material and Research Methodology
The stomach of the first wolf cub contained a fragment of woolly rhinoceros tissue. This discovery provided a rare opportunity to study the genetic makeup of Coelodonta antiquitatis, the scientific name for the woolly rhinoceros, which became extinct around 14,000 years ago. Scientists successfully decoded the rhinoceros's entire genome from the partially digested tissue. This marks the first instance of an Ice Age animal's complete genome being sequenced from the stomach contents of another animal, and it represents the youngest woolly rhinoceros genome obtained to date.
The research, published in Genome Biology and Evolution, involved differentiating wolf and rhino DNA, a challenge due to their identical age. Researchers utilized the Sumatran rhinoceros, the woolly rhino's closest living relative, as a genetic guide. The newly sequenced genome was then compared with those from two older woolly rhino specimens, dated 18,000 and 49,000 years ago, to assess changes in genetic diversity, including inbreeding levels and harmful mutations over time. The specific circumstances of how the wolf cub consumed the rhinoceros tissue remain unknown.
Insights into Woolly Rhinoceros Extinction
The study found no evidence of genetic deterioration, such as high inbreeding or accumulation of harmful mutations, in the woolly rhinoceros population as it approached extinction. This finding suggests that the species' population remained relatively large and stable, contradicting prior assumptions of genomic erosion typically observed in declining species.
This stability indicates that the extinction event was likely sudden, possibly occurring within 300 to 400 years before the species' final disappearance. Professor Love Dalén, an evolutionary genomics expert and coauthor of the study, stated that woolly rhinos coexisted with humans in the region for approximately 15,000 years after human arrival. These findings suggest that climate warming, rather than human hunting, was the primary cause of their extinction.
The research points to an abrupt warming period during the last ice age, known as the Bølling-Allerød Interstadial, which occurred between 14,700 and 12,900 years ago. This period is believed to have significantly altered the landscape, contributing to the rapid demise of the woolly rhinoceros. The preservation of the wolf cub in permafrost provided a unique window into understanding ancient ecosystems and the diets of extinct animals.