In Depth
Ursus spelaeus, better known as the cave bear is by far one of the most common Pleistocene mammals in the fossil record, thanks mainly due to its behaviour of frequenting caves. In fact the fossils of Ursus spelaeus are so numerous that in World War I the German army used them as a source of phosphates.
The huge numbers of cave bear fossils in caves that have been documented to represent thousands of individuals to a single cave strongly suggests that this bear regularly spent time in caves, perhaps returning to rest after foraging.
Bears that we know today by contrast only frequent caves during the hibernation period and sleep outdoors during the warmer months. The immense number of Ursus spelaeus fossils in certain caves has also led to the theory that these bears may have actually lived in social groups, although in depth study of the layers and dating has suggested that the remains are of single individual bears building up over the course of the Pleistocene period.
As older remains became buried by sediment and fossilised they would have been of no nutritional value to anything and would have been left alone to accumulate, giving the impression of several bears living together rather than just one or two.
Cave bears have long been thought to be herbivorous animals, meaning that they only ate plants.
Key evidence for this comes from the lack of premolar teeth that are usually absent in herbivores resulting in a gap between the forwards canines and rear molars called a diastema. Isotope analysis has also yielded low amounts of carbon-13 and nitrogen-15 which are usually found in high concentrations in carnivores.
Counter to the strictly herbivorous diet theory however is the presence of some fossils that do have elevated levels of nitrogen-15, as, well as tooth wear associated with the gnawing of bones.
Additionally some cave bear fossils also have tooth marks on them that seem to have been caused by others of their species. Not only does this suggest that cave bears occasionally ate meat, they may have scavenged the dead bodies of other cave bears that had died in caves.
This is why Ursus spelaeus is today considered by most to have been an opportunistic omnivore that relied mostly upon eating plants, but would also supplement its diet with occasional meat when it was able to.
As one might expect cave bears were most common in areas that had large amounts of caves, particularly limestone that would have had caves carved out by water over several eons.
As such cave bears lived in ecosystems that were between lowland plains and high level mountains that would have had a greater variety of trees and vegetation growing in them. Aside from offering a greater variety of food, a habitat preference such as this suggests that Ursus spelaeus did not compete with other European megafauna such as the woolly rhino and the woolly mammoth since they inhabited more open areas.
Cave bears could also range across most of Europe, settling where they encountered suitable habitats, because the lower sea levels meant that marine boundaries such as the English Channel and North Sea did not exist.
A greater determining factor in the range of cave bears was the amount of glacial cover, something that would have expanded and receded over varying periods.
Ursus spelaeus individuals from both milder and harsher times are known, with the individuals present in harsher times growing slightly larger than the bears that lived in slightly warmer times.
This is a simple strategy where growing bigger creates a greater level of outer insulation while the total surface area of the body still increases but at proportionately less amount than the total body mass.
This has been repeated and documented many times for different mammals that live in colder climates that all grow proportionately bigger that their closest related genera, perhaps the most relevant example here being the polar bear (Ursus maritimus) which does well in arctic conditions, but has been seen to overheat when kept in zoos in warmer climates.
Returning to the large collections of remains mentioned above, it’s clear that large numbers of Ursus spelaeus died in caves, but this needs further investigation.
Because the remains of cave bears accumulated over tens of thousands of years it is easy to immediately discount the possibility of cave ins, as such an event would have only trapped one bear and then prevented others from entering.
One widely accepted theory is that cave bears that did not eat enough food during the summer months to build up their fat reserves ended up starving to death as they slumbered. Even today animals that rely upon hibernation to last out the colder winter are vulnerable in times where plants do not grow or produce as much sustenance as they usually do, and back in the Pleistocene when ice sheets were toing and froing across Europe food would have been even more unpredictable from year to year.
More in depth study of some cave bear remains has revealed that bone disorders such as rickets, periostitus and osteomyelitis were quite common including other ailments such as the presence of tumours.
Although not necessarily fatal to the individuals these bones belonged to, they would have impeded their ability to forage, slowly bringing the animal down to the point where it could no longer support itself. In these weakened states its thought that cave bears may have even fallen as prey to cave hyenas as well as even the European cave lion, that otherwise may have given a healthy bear in the prime of its life a wide birth.
Ultimately as a species, cave bears seem to have succumbed to the effects of habitat loss, as by only living in caves these bears would have only ever had a set amount of areas available to them.
However as the Pleistocene was reaching its final stages, Neanderthals were beginning to become more common, and these primitive people also used caves for shelter. Inevitably one species would have to give way, and it was the cave bear that lost out to the greater numbers and intelligence of Neanderthals.
However despite the fact that they seem to have taken over, Neanderthals also seem to have held cave bears in very high regard.
There are several burial sites in Europe where the remains of several bears have been assembled in pits and then covered with stone slabs. Perhaps the most famous site is Drachenloch, Switzerland where seven cave bear skulls are arranged to face the front of the cave, while six more are placed in recessed notches in the cave wall further in.
Further remains were found bundled together, along with a skull of a three year old juvenile bear that had had its cheek pierced by the leg bone of another juvenile bear.
Although some researchers claim that these are natural occurrences, there are a great many other who believe that remains like these are those of an ancient bear cult. How and why bears would be worshipped is uncertain, but it could be for anything from a totem animal, to a guardian of the caves against intruders, to maybe even a ward against other cave bears wandering in to Neanderthal settlements.
Further Reading
- On the phylogeny of Eurasian bears. – Palaeontographica Abteilung A 230: 1–32. – P. Mazza & M. Rustioni – 1994.
- What size were Arctodus simus and Ursus spelaeus (Carnivora: Ursidae)? – Annales Zoologici Fennici 36: 93–102. – Per Christiansen – 1999.
- Ancient DNA analysis reveals divergence of the cave bear, Ursus spelaeus, and brown bear, Ursus arctos, lineages. – Current Biology 11 (3): 200–203. – Odile Loreille, Ludovic Orlando, Marylène Patou-Mathis, Michel Philippe, Pierre Taberlet & Catherine Hänni – 2001.
- Genomic Sequencing of Pleistocene Cave Bears. – Science 309 (5734): 597–599.- James P. Noonan, Michael Hofreiter, Doug Smith, James R. Priest, Nadin Rohland, Gernot Rabeder, Johannes Krause, J. Chris Detter, Svante Pääbo & Edward M. Rubin – 2005.
- Comparative dental microwear analysis of cave bears Ursus spelaeus Rosenmüller, 1794 and brown bears Ursus arctos Linnaeus ,1758. – Scientific Annals, School of Geology Aristotle University of Thessaloniki (AUTH). Special 98: 103–108. – A. C. Pinto Llono – 2006.
- Prey deposits and den sites of the Upper Pleistocene hyena Crocuta crocuta spelaea (Goldfuss, 1823) in horizontal and vertical caves of the Bohemian Karst (Czech Republic). Bulletin of Geosciences 81(4), 237–276 (25 figures). – Czech Geological Survey, Prague. ISSN 1214-1119. – C. G. Diedrich & K. Zak – 2006.
- Isotopic evidence for omnivory among European cave bears: Late Pleistocene Ursus spelaeus from the Pestera cu Oase, Romania.- PNAS 105: 100–104. – Michael P. Richards, Martina Pacher, Mathias Stiller, Jérôme Quilès, Michael Hofreiter, Silviu Constantin, João Zilhão, and Erik Trinkaus – 2008.
- Reply to Grandal and Fernández: Hibernation can also cause high δ15N values in cave bears. – Proceedings of the National Academy of Sciences of the United States of America 105 (11): E15. doi:10.1073/pnas.0801137105 – Erik Trinkaus & Michael P. Richards – 2008.
- Extinction chronology and palaeobiology of the cave bear (Ursus spelaeus). – Boreas 38 (2): 189–206 – M. Pacher & A. J. Stuart – 2009.
- Ecomorphological correlates of craniodental variation in bears and paleobiological implications for extinct taxa: an approach based on geometric morphometrics – Journal of Zoology Volume 277, Issue 1, pages 70–80 – B. Figueirido, P. Palmqvist & J. A. Pérez-Claros – 2010.
- Withering Away – 25,000 Years of Genetic Decline Preceded Cave Bear Extinction. – Molecular Biology and Evolution 27 (5): 975–978. – Mathias Stiller, Gennady Baryshnikov, Hervé Bocherens, Aurora Grandal d’Anglade, Brigitte Hilpert, Susanne C. Münzel, Ron Pinhasi, Gernot Rabeder, Wilfried Rosendahl, Erik Trinkaus, Michael Hofreiter & Michael Knapp – 2010.
