An Ice Age dietary surprise
In the mountainous Surkhandarya Region of southern Uzbekistan, paleontological finds have challenged long-held ideas about the diet of Ice Age megafauna. The remains belong to Ursus ingressus, a species of cave bear, and date to the Late Pleistocene, approximately 25,000 years ago. These bears lived at high altitudes, an unusual setting for this species, which was more commonly found in medium and high elevation zones across Central and Eastern Europe. The discovery is located in the western spurs of the Gissar Range, a part of the greater Pamir-Alay mountain system.
Traditionally, many bear species, both living and extinct, are considered omnivores, consuming a mix of plants, meat, and fish. Some studies on Ursus ingressus from other regions suggested an omnivorous diet that included more animal protein than modern brown bears. Other research pointed to a more herbivorous lifestyle. The Surxon Daryo remains provided a unique opportunity to test these hypotheses in a Central Asian context. The way to understand their diet was in the chemical composition of their bones.
The isotopic evidence
Scientists used stable isotope analysis on the bone collagen of the Surxon Daryo bears to reconstruct their diet. This technique examines the ratios of different stable isotopes of elements like carbon and nitrogen. The ratio of Carbon-13 to Carbon-12 (expressed as δ¹³C) reveals the types of plants an animal ate. The ratio of Nitrogen-15 to Nitrogen-14 (δ¹⁵N) indicates the animal's trophic level, its position in the food chain.
The results were conclusive. The isotopic signatures in the bones showed that these high-altitude cave bears had a diet consisting almost entirely of terrestrial plants. Unlike many modern brown bears that feed on salmon, or other prehistoric bear populations that consumed meat, this group was strictly herbivorous. Their specialized diet of high-altitude grasses and other vegetation was a successful adaptation to the cold and arid environment of Pleistocene Central Asia. This dietary inflexibility, however, may have been a factor in the species' eventual extinction as climate conditions changed and plant resources fluctuated.