Retreat and extinction of the Late Pleistocene cave bear (Ursus spelaeus sensu lato)

Abstract

The cave bear (Ursus spelaeus sensu lato) is a typical representative of Pleistocene megafauna which became extinct at the end of the Last Glacial. Detailed knowledge of cave bear extinction could explain this spectacular ecological transformation. The paper provides a report on the youngest remains of the cave bear dated to 20,930 ± 140 ¹⁴C years before present (BP). Ancient DNA analyses proved its affiliation to the Ursus ingressus haplotype. Using this record and 205 other dates, we determined, following eight approaches, the extinction time of this mammal at 26,100-24,300 cal. years BP. The time is only slightly earlier, i.e. 27,000-26,100 cal. years BP, when young dates without associated collagen data are excluded. The demise of cave bear falls within the coldest phase of the last glacial period, Greenland Stadial 3. This finding and the significant decrease in the cave bear records with cooling indicate that the drastic climatic changes were responsible for its extinction. Climate deterioration lowered vegetation productivity, on which the cave bear strongly depended as a strict herbivore. The distribution of the last cave bear records in Europe suggests that this animal was vanishing by fragmentation into subpopulations occupying small habitats. One of them was the Kraków-Częstochowa Upland in Poland, where we discovered the latest record of the cave bear and also two other, younger than 25,000 ¹⁴C years BP. The relatively long survival of this bear in karst regions may result from suitable microclimate and continuous access to water provided by deep aquifers, indicating a refugial role of such regions in the Pleistocene for many species.

Keywords: Ancient DNA; Cave bear; Extinction; Last glacial maximum; Megafauna; Refugium.

Fig. 1

Localization of cave bears (Ursus spelaeus sensu lato) remains younger than 26,000 ¹⁴C years BP in Europe including the latest record confirmed genetically from the Stajnia Cave

Fig. 2

The third phalanx (JST4) excavated in the Stajnia Cave and confirmed genetically as belonging to the cave bear Ursus ingressus

Fig. 3

Differences between the sequence from the Stajnia Cave and other classified cave bears (Ursus kudarensis, ingressus, spelaeus) and the brown bear (Ursus arctos). The results clearly indicate a close similarity of the Stajnia sample to Ursus ingressus

Fig. 4

MrBayes phylogenetic tree for cave bears (Ursus kudarensis, ingressus, rossicus, spelaeus) and the brown bear (Ursus arctos) mtDNA control region. The sequence from the Stajnia sample indicated by an arrow groups significantly within U. ingressus clade. Values at nodes correspond in the order to: posterior probabilities estimated in MrBayes, support values calculated in morePhyML based on a Shimodaira-Hasegawa-like procedure and bootstrap values obtained in PhyML. Values for probabilities and bootstrap percentages lower than 0.50 and 50 %, respectively, were omitted

Fig. 5

Haplotype network of cave bears (Ursus kudarensis, ingressus, spelaeus) and the brown bear (Ursus arctos). The haplotype from the Stajnia Cave occupies the central position within U. ingressus haplotypes

Fig. 6

Distribution of the cave bear (Ursus spelaeus sensu lato) dates (yellow bars) with fitted density functions of lognormal distribution (red line). The function was averaged for two distributions with one of the dates for the Stajnia sample (Poz-61719 or GdA-3894)

Fig. 7

Distribution of late dates of the cave bear (Ursus spelaeus sensu lato) samples in the time scale (yellow diamonds). The youngest date of the Stajnia sample confirmed genetically was indicated (Poz-61719). The red curve in the upper part corresponds to the density function averaged for distributions with one of the dates for the Stajnia sample. Symbols above the curve indicate cave bear extinction times for two data sets, including the Stajnia Poz-61719 date (circles) or GdA-3894 date (squares), estimated by methods: SS Strauss and Sadler (1989), S Solow (1993), M McInerny et al. (2006), SR Solow and Roberts (2003), RS Roberts and Solow (2003), BRIWM Saltré et al. (2015) and GRIWM Bradshaw et al. (2012). Horizontal bars indicate 95 % confidence interval for BRIWM and GRIWM methods. Two standard deviations for the Poz-61719 date are also marked by a short black vertical line (2SD). The results were compared with the revised Greenland ice core δ¹⁸O curve (in black) developed by combining the Cariaco Basin (Hulu Cave) and Greenland ice core (GICC05) records (Cooper et al. 2015). Corresponding Greenland stadials (GS) and interstadials (GI) as well as strict definition of the Last Glacial Maximum (LGM) were marked. The results show that the cave bear became extinct in the middle of the cold stadial GS-3