Bears of the Pleistocene

[brotherbear]

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5059403/

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

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.

The extinction of large-bodied mammals (called megafauna) is one of the most characteristic and inherent features of the Late Pleistocene. The disappearance began 50,000 years ago and affected a substantial number of mammalian genera, e.g. 36 % of them in Eurasia, 72 % in North America and 83 % in South America (Barnosky et al. 2004). Both the climate and environment changes, as well as human influence, are believed to be the main causes of this extinction (Barnosky et al. 2004; Cooper et al. 2015; Koch and Barnosky 2006; Lorenzen et al. 2011; Stuart 2015). The climate shift was sufficient to explain the fauna transformation in some cases, but in others, a combination of climatic and anthropogenic effects was most probably responsible for this phenomenon (Cooper et al. 2015; Lorenzen et al. 2011).

A typical representative of megafauna is the cave bear (Ursus spelaeus sensu lato), which was one of the most widespread mammals in Eurasia in the Late Pleistocene. It evolved from Middle Pleistocene Ursus deningeri and developed into several forms which can be distinguished at morphological and genetic levels. Two main European forms in the species rank, which diverged probably between 414,000 and 173,000 years ago, were identified as Ursus ingressus, which inhabited south-eastern and central Europe as well as the Ural (Baca et al. 2014; Rabeder et al. 2004b), and U. spelaeus, which lived mainly in western Europe, although its remains were found also in the Altai (Knapp et al. 2009; Rabeder et al. 2004b). According to the rules of the International Code of Zoological Nomenclature, U. ingressus should, however, be called Ursus kanivetz, because under the latter name a bear from Medvezhiya Cave in the Ural was first described by Vereshchagin (1973) (see also Baryshnikov and Puzachenko (2011)). Further studies of ancient DNA showed that the haplotype from Medvezhiya Cave is clustered with others from Europe, described as U. ingressus (Baca et al. 2012; Knapp et al. 2009). Additionally, two small cave bear forms that had preserved some primitive traits were distinguished as subspecies of U. spelaeus: U. spelaeus eremus and U. spelaeus ladinicus (Rabeder and Hofreiter 2004; Rabeder et al. 2004a). Their distribution was confined to the high alpine caves in Austria and Italy. Recently, another major group of large cave bears from the Caucasus and the Yana River region in eastern Siberia was discovered (Baryshnikov 1998; Knapp et al. 2009). Initially, they were named Ursus deningeri kudarensis, but recent genetic studies suggest that they should be considered a third species, U rsus kudarensis (Stiller et al. 2014). 
 
By the end of the Pleistocene, all these cave bear forms were extinct and the causes and timing of this process have been debated over the recent years. Direct radiocarbon dating indicates that the last cave bears became extinct prior to the Last Glacial Maximum (LGM) and disappeared from fossil record quite simultaneously in different parts of Europe about 24,000 14C years before present (BP) (about 28,000 cal. years BP) (Bocherens et al. 2014; Hofreiter et al. 2002; Martini et al. 2014; Pacher and Stuart 2009; Sabol et al. 2014; Wojtal et al. 2015). Paleogenetic analyses showed, nonetheless, that the demise of cave bears started ca. 50,000 radiocarbon years BP (Stiller et al. 2010), thus about 25,000 years before their final extinction. It has been argued that apart from the changing climate (Pacher and Stuart 2009; Stuart and Lister 2007), several other factors contributed to the decline of cave bears. There is compelling evidence for human hunting of cave bears (Münzel et al. 2011; Wojtal et al. 2015), as well as their competition for caves as a shelter (Grayson and Delpech 2003). Possibly, also large carnivores like cave lion (Panthera spelaea) and cave hyena (Crocuta crocuta spelaea) hunted cave bears while these were hibernating (Bocherens et al. 2011a; Diedrich 2014).



The paper reports on, so far, the youngest remains of the cave bear from the Stajnia Cave located in the Częstochowa Upland, Poland. In this region were also found other quite young fossils of this bear in two caves, Komarowa and Deszczowa (Nadachowski et al. 2009; Wojtal 2007; Wojtal et al. 2015). Genetic analyses confirmed beyond doubt the affiliation of this specimen to the cave bear, whereas the direct radiocarbon dating provided the evidence for the survival of this species into the Greenland stadial GS-3. Using this new dating and more than 200 published dates, we estimated the time of cave bear extinction and discussed potential factors of its disappearance and survival in karst regions. 

 
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