Cave bear

The cave bear (Ursus spelaeus) was a species of bear that lived in Europe during the Pleistocene and became extinct at the beginning of the Last Glacial Maximum, about 27,500 years ago.

Both the name "cave" and the scientific name spelaeus derive from the fact that fossils of this species were mostly found in caves, indicating this species spent more time in caves than the brown bear, which only uses caves for hibernation. Consequently, in the course of time, whole layers of bones, almost entire skeletons, were found in many caves.

Taxonomy
Cave bear skeletons were first described in 1774 by Johann Friederich Esper in his book Newly Discovered Zoolites of Unknown Four Footed Animals. Originally thought to belong to dragons, unicorns, apes, canids or felids, Esper postulated 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, most researchers held little respect for them. During World War I, large amounts of cave bear bones were used as a source of phosphates, leaving behind little more than skulls and leg bones.[1]

Many caves in Central Europe have skeletons of cave bears inside, for example the Heinrichshöhle in Hemer or the Dechenhöhle in Iserlohn, Germany. In Romania, in a cave called Bears' Cave, 140 cave bear skeletons were discovered in 1983.

Evolution
Both the cave bear and the brown bear are thought to be descended from the Plio-Pleistocene Etruscan bear (Ursus etruscus)[3][4][5] that lived about 5.3 Mya to 10,000 years ago. The last common ancestor of cave bears and brown bears lived between 1.2 and 1.4 Mya.[6] 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.[7][8] 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,[9] while other authorities consider both taxa to be chronological variants of the same species.[10]

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, known as 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.

Description
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.[12] Cave bears were comparable in size to the largest modern-day bears. The average weight for males was 400 to 500 kilograms (880 to 1,100 lb), while females weighed 225 to 250 kg (495 to 550 lb).[13] 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.[14]

Cave bears of the last Ice Age lacked the usual two or three premolars present in other bears; to compensate, the last molar is very elongated, with supplementary cusps.[15] The humerus of the cave bear was similar in size to that of the polar bear, as were the femora of females. The femora of male cave bears, however, bore more similarities in size to those of kodiak bears.