Cave bear
The cave bear is a prehistoric 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.
The common and scientific name for the species comes from their remains having been largely been found caves. This reflects the views of experts that cave bears spent more time in caves than the brown bear, frequently using them to hibernate during the winter months. Unlike brown bears, cave bears are thought to have been almost entirely or exclusively herbivorous.
Cave bears exhibit a great degree of size, morphological and genetic variability, and Late Pleistocene cave bears are often considered to be species complex of up to 6 different species.
Taxonomy
Cave bear skeletons were first described in 1774 by Johann Friedrich 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 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 was 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, such as the Heinrichshöhle in Hemer and the Dechenhöhle in Iserlohn, Germany. A complete skeleton, five complete skulls, and 18 other bones were found inside Kletno Bear Cave, in 1966 in Poland. In Romania, in a cave called Bears' Cave, 140 cave bear skeletons were discovered in 1983.
Remains assigned to "cave bears" sensu lato from the Late Pleistocene exhibit a strong degree of morphological and size variability, and have often been assigned to their own species, including Ursus rossicus '', Ursus ingressus, Ursus kanivetz, Ursus kudarensis, Ursus eremus and Ursus spelaeus sensu stricto. These populations/species show considerable genetic divergence from each other, though whether these species should be regarded as synonyms of U. spelaeus'' is debated.
Evolution
Both the cave bear and the brown bear are thought to be descended from the Early Pleistocene species Ursus etruscus. The date of divergence between the ancestors of cave bears and brown bears has been estimated at around 1.2-1.5 million years ago. The earliest remains of the cave bear lineage are assigned to the species Ursus deningeri '', which first appears in the fossil record at the end of the Early Pleistocene, around 1.2-0.8 million years ago. U. deningeri is known from remains spanning from Europe to China. The transition between Ursus deningeri and Ursus spelaeus is often 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 anywhere will 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, 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.. However, a recent study showed that both species had some hybridization between them.
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. Cave bears were comparable in size to, or larger than, the largest modern-day bears, measuring up to in length. The average weight for males was, while females weighed. Of cave bear skeletons in museums, 90% are classified as 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.The morphology of the mandible of cave bears varied depending on climate; individuals in colder, drier, and more seasonal climates possessed more slender mandibles and a dorsoventrally smaller mandibular ramus relative to individuals living in warmer and wetter conditions. 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. 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.
Behaviour
Dietary habits
Cave bear teeth were very large and show greater wear than most modern bear species, suggesting a diet of tough materials. However, tubers and other gritty food, which cause distinctive tooth wear in modern brown bears, do not appear to have constituted a major part of cave bears' diets on the basis of dental microwear analysis. Seed fruits are documented to have been consumed by cave bears. Cave bear dental microwear from the high altitude site of Ramesch-Knochenhöhle in the Totes Gebirge indicates that some cave bears living in mountains ingested large amounts of sand as a result of feeding on alpine vegetation. The results from Ramesch-Knochenhöhle also indicate two very distinct patterns of microwear among the same subspecies, which may potentially reflect differences in feeding behaviour between male and female cave bears.The morphological features of the cave bear chewing apparatus, including loss of premolars, have long been suggested to indicate their diets displayed a higher degree of herbivory than the Eurasian brown bear. Indeed, a solely vegetarian diet has been inferred on the basis of tooth morphology. Results obtained on the stable isotopes of cave bear bones also point to a largely vegetarian diet in having low levels of nitrogen-15 and carbon-13, which are accumulated at a faster rate by carnivores as opposed to herbivores. Among Mediterranean cave bears such as those found in Toll Cave in northeastern Spain, the particularly low δ15N values may be a result of their high intake of nitrogen-fixing plants.
However, some evidence points toward the occasional inclusion of animal protein in cave bear diets. For example, toothmarks on cave bear remains in areas where cave bears are the only recorded potential carnivores suggests occasional cannibalistic scavenging, possibly on individuals that died during hibernation, and dental microwear analysis indicates the cave bear may have fed on a greater quantity of bone than its contemporary, the smaller Eurasian brown bear. The dental microwear patterns of cave bear molars from the northeastern Iberian Peninsula show that cave bears may have consumed more meat in the days and weeks leading up to hibernation. Cave bear dental microwear from Belgium has also showed clear evidence of their omnivory during predormancy, with bone, insect, and mammal meat consumption being inferred from the microwear patterns. Comparisons of the dental microwear and macrowear of brown bears and cave bears in northern Spain found that the latter were significantly more osteophagous than the former. Additionally, cave bear remains from Peștera cu Oase in the southwestern tip of the Romanian part of the Carpathian Mountains had elevated levels of nitrogen-15 in their bones, indicative of omnivorous diets, although the values are within the range of those found for the strictly herbivorous mammoth. One stable isotopic study concluded that the degree of omnivory in cave bears was similar to that in modern brown bears.
Although the current prevailing opinion concludes that cave bears were largely herbivorous, and more so than any modern species of the genus Ursus, increasing evidence points to omnivorous diets, based both on regional variability of isotopic composition of bone remains indicative of dietary plasticity, and on a recent re-evaluation of craniodental morphology that places the cave bear squarely among omnivorous modern bear species with respect to its skull and tooth shapes.