Ursus spelaeus

The cave bear (Ursus spelaeus) was a species of bear that lived in Europe and Asia during the Pleistocene and became extinct about 24,000 years ago during the Last Glacial Maximum. Both the word 'cave' and the scientific name spelaeus are used because fossils of this species were mostly found in caves. This reflects the views of experts that cave bears may have spent more time in caves than the brown bear, which uses caves only for hibernation. Cave bear skeletons were first described in 1774 by Johann Friederich Esper in his book Newly Discovered Zoolites of Unknown Four Footed Animals. While scientists at the time considered that the skeletons could belong to apes, canids, felids, or even dragons or unicorns, Esper postulated that they actually belonged to polar bears. Twenty years later, Johann Christian Rosenmüller, an anatomist at the Leipzig University, gave the species its binomial name. The bones were so numerous that most researchers had little regard for them. During World War I, with the scarcity of phosphate dung, earth from the caves where cave bear bones occurred were used as a source of phosphates. When the 'dragon caves' in Austria's Styria region were exploited for this purpose, only the skulls and leg bones were kept. Many caves in Central Europe have skeletons of cave bears inside, for example the Heinrichshöhle in Hemer, the Dechenhöhle in Iserlohn, Germany. A complete skeleton, five complete skulls, and 18 other bones were found inside Jaskinia Niedźwiedzia (bear cave) in 1966 in Poland. In Romania, in a cave called Bears' Cave, 140 cave bear skeletons were discovered in 1983. Both the cave bear and the brown bear are thought to be descended from the Plio-Pleistocene Etruscan bear (Ursus etruscus) that lived about 5.3 Mya to 100,000 years ago. The last common ancestor of cave bears and brown bears lived between 1.2–1.4 Mya. The immediate precursor of the cave bear was probably Ursus deningeri (Deninger's bear), a species restricted to Pleistocene Europe about 1.8 Mya to 100,000 years ago. The transition between Deninger's bear and the cave bear is given as the last interglacial, although the boundary between these forms is arbitrary, and intermediate or transitional taxa have been proposed, e.g. Ursus spelaeus deningeroides, while other authorities consider both taxa to be chronological variants of the same species. Cave bears found in different regions vary in age, thus facilitating investigations into evolutionary trends. The three anterior premolars were gradually reduced, then disappeared, possibly in response to a largely vegetarian diet. In a fourth of the skulls found in the Conturines, the third premolar is still present, while more derived specimens elsewhere lack it. The last remaining premolar became conjugated with the true molars, enlarging the crown and granting it more cusps and cutting borders. This phenomenon, called molarization, improved the mastication capacities of the molars, facilitating the processing of tough vegetation. This allowed the cave bear to gain more energy for hibernation, while eating less than its ancestors. In 2005, scientists recovered and sequenced the nuclear DNA of a cave bear that lived between 42,000 and 44,000 years ago. The procedure used genomic DNA extracted from one of the animal's teeth. Sequencing the DNA directly (rather than first replicating it with the polymerase chain reaction), the scientists recovered 21 cave bear genes from remains that did not yield significant amounts of DNA with traditional techniques. This study confirmed and built on results from a previous study using mitochondrial DNA extracted from cave bear remains ranging from 20,000 to 130,000 years old. Both show that the cave bear was more closely related to the brown bear and polar bear than it was to the American black bear, but had split from the brown bear lineage before the distinct eastern and western brown bear lineages diversified and before the split of brown bears and polar bears. The divergence date estimate of cave bears and brown bears is about 1.2–1.4 Mya. However, a recent study showed that both species had some hybridization between them. The cave bear had a very broad, domed skull with a steep forehead. Its stout body had long thighs, massive shins and in-turning feet, making it similar in skeletal structure to the brown bear. Cave bears were comparable in size to the largest modern-day bears. The average weight for males was 350 to 600 kg (770 to 1,320 lb), though some specimens weighed as much as 1000 kg (2,200 lb), while females weighed 225 to 250 kg (495 to 550 lb). Of cave bear skeletons in museums, 90% are male due to a misconception that the female skeletons were merely 'dwarfs'. Cave bears grew larger during glaciations and smaller during interglacials, probably to adjust heat loss rate.