Cave bear

Cave Bear Fossil range: Middle to Late Pleistocene
Mounted cave bear skeleton
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Mammalia
Order:	Carnivora
Family:	Ursidae
Genus:	Ursus
Species:	U. spelaeus
Binomial name
Ursus spelaeus Rosenmüller, 1794

The Cave Bear (Ursus spelaeus) was a species of bear which 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 Bear and the scientific name spelaeus derive from the fact that fossils of this species were mostly found in caves, indicating that 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 entirely those of cave bears, were found in many caves.

History of cave bear discoveries

Rearing Ursus spelaeus skeleton

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 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. Cave bear bones were so numerous, that 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 Europe have skeletons of cave bears on display, for example the Heinrichshöhle in Hemer or the Dechenhöhle in Iserlohn, Germany. In Romania, there is a cave called Peştera Urşilor (Bears' Cave) where 140 cave bear skeletons were discovered in 1983.[1]

Description and Biology

Range and habitat

The cave bear's range stretched across Europe; from Spain to Eurasia, from Italy and Greece to Belgium, the Netherlands and possibly Great Britain, across a portion of Germany through Poland, then south into Hungary, Romania and parts of Russia, Caucasus and northern Iran. There have been no traces of cave bears living in northern Britain, Scandinavia or the Baltic countries, which were covered in extensive glaciers at the time. The largest numbers of cave bear remains have been found in Austria, Switzerland, southern Germany, northern Italy, northern Spain, Croatia, Hungary and Romania. The huge number of bones found in south, central and east Europe has led some scientists to think that Europe may have once had literal herds of cave bears. Some however point out that though some caves have thousands of bones, they were accumulated over a period of 100,000 years or more, thus requiring only two deaths in a cave per year to account for the large numbers.^[1]

The cave bear inhabited low mountainous areas, especially in regions rich in limestone caves. They seemed to avoid open plains, preferring forested or forest-edged terrains^[1].

Anatomy

Life restoration

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.^[2] Cave bears were comparable in size to the largest modern day bears. The average weight for males was 400-500 kilograms (880-1102 pounds), while females weighed 225–250 kg (496-551 lbs).^[3] 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.^[4] Cave bears of the last ice age lacked the usual 2-3 premolars present in other bears; to compensate, the last molar is very elongated, with supplementary cusps.^[5] 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.^[3]

Dietary habits

Cave bear teeth 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' diet on the basis of dental microwear analysis.^[6]

Skull of Ursus spelaeus. Cave bears lacked the usual 2-3 premolars present in other bear species

The morphological features of the cave bear chewing apparatus, including loss of premolars, have long been suggested to indicate that their diets displayed a higher degree of herbivory than the Eurasian brown bear.^[7] Indeed, a solely vegetarian diet has been inferred on the basis of tooth morphology.^[8] 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,^[9] which are accumulated at a faster rate by meat eaters as opposed to herbivores.

However, some evidence points toward inclusion of at least occasional animal protein in the cave bear diet. For example, toothmarks on cave bear remains in areas where cave bears are the only recorded potential carnivores suggests occasional cannibalistic scavenging^[10][11], possibly on individuals that died during hibernation, and dental microwear analysis indicates that the cave bear may have fed on a greater quantity of bone than its contemporary, the smaller Eurasian Brown Bear.^[12] Additionally, cave bear remains from Peştera cu Oase in the southwestern tip of the Carpathian mountains had elevated levels of nitrogen-15 in their bones, indicative of an omnivorous diet,^[13] although the values are within the range of those found for the strictly herbivorous mammoth.^[14]

Although the current prevailing opinion concludes that cave bears were largely herbivorous, and more so than any modern species of the genus Ursus,^[15] increasing evidence points to an omnivorous diet, based both on regional variability of isotopic composition of bone remains indicative of dietary plasticity,^[13] and on a recent reevaluation of its craniodental morphology that places the cave bear squarely among omnivorous modern bear species with respect to its skull and tooth shapes.^[16]

Mortality

Standing skeleton of juvenile cave bear

Death during hibernation was a common end for cave bears, mainly befalling specimens that failed ecologically during the summer season through inexperience, sickness or old age.^[17] Some cave bear bones show signs of numerous different ailments, including fusion of the spine, bone tumours, cavities, tooth resorption, necrosis (particularly in younger specimens), osteomyelitis, periostitis, rickets and kidney stones.^[2] Male cave bear skeletons have been found with broken baculums, probably due to fighting during breeding season.^[17] Cave bear longevity is unknown, though it has been estimated that they seldom exceeded 20 years of age.^[1] Paleontologists doubt adult cave bears had any natural predators, save for pack hunting wolves and cave hyenas which would probably have attacked sick or infirm specimens^[1]. Cave hyenas are thought to be responsible for the dis-articulation and destruction of some cave bear skeletons. Such large carcasses were an optimal food resource for the hyenas, especially at the end of the winter, when food was scarce.^[18] The presence of fully articulated adult cave lion skeletons, deep in cave bear dens, indicates that lions may have occasionally entered dens to prey on cave bears, with some dying in the attempt.^[19]

Evolution

Skeleton mounted in quadrupedal posture

Both the cave bear and the brown bear are thought to be descended from the Plio-Pleistocene Etruscan bear (Ursus etruscus)^[7][8][20] that lived ~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 million years ago.^[21] The immediate precursor of the cave bear was probably Ursus deningeri (Deninger's bear), a species restricted to Pleistocene Europe ~1.8 Mya to 100,000 years ago.^[22][23] 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,^[24] while other authorities consider both taxa to be chronological variants of the same species.^[25]

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.^[26]

Recovery of fossil DNA

In May 2005, scientists in California succeeded in recovering and sequencing nuclear DNA of a cave bear that lived between 42,000 and 44,000 years ago. The procedure used genomic DNA extracted from the animal's tooth. Sequencing the DNA directly (rather than first replicating it with the polymerase chain reaction), the scientists were able to recover 21 cave bear genes from remains that did not yield significant amounts of DNA with traditional techniques.^[27] 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.^[21] Both show the cave bear to be more closely related to the brown bear and polar bear than the American black bear, but having split from the brown bear lineage prior to the diversification of distinct eastern and western brown bear lineages and prior to the split of brown bears and polar bears. The divergence date estimate of cave bears and brown bears is ~1.2-1.4 Mya.^[21]

Causes of extinction

Recent reassessment of fossils indicate the cave bear probably died out 27,800 years ago. Though the reason is still disputed, the timing supports habitat loss due to climate change as responsible. Compared with other megafaunal species that also became extinct during the last Glacial Maximum, the cave bear had a more specialized diet of high quality plants and a relatively restricted geographical range which is suggested as an explanation as to why it died out so much earlier than the rest.^[15] Certain experts dispute this claim, as the cave bears had survived multiple times of climate change. Overhunting by humans has been largely dismissed because human populations at the time were too small to pose a serious threat to the cave bear's survival, though there is evidence that the two species may have competed for living space in caves.^[1] Also, unlike brown bears, cave bears are seldom represented in cave paintings. This has led some experts to believe that the cave bear may have been avoided by human hunters,^[28] or their habitat preferences may not have overlapped. One theory proposed by late paleontologist Bjorn Kurten states that the cave bear populations were fragmented and under stress even before the advent of the glaciers.^[1] It is possible that populations living south from the Alps survived significantly longer.^[15]

Cave bear worship

Collections of bear bones at several widely dispersed sites suggest that Neanderthals may have worshipped cave bears, especially at Drachenloch, in Switzerland, where a stone chest was discovered with a number of bear skulls stacked upon it. Neanderthals, who also inhabited the entrance of the cave, are believed to have built it. A massive stone slab covered the top of the structure. At the cave entrance, seven bear skulls were arranged with their muzzles facing the cave entrance, while still deeper in the cave, a further six bear skulls were lodged in niches along the wall. Next to these remains were bundles of limb bones belonging to different bears. Consequently, it was at this site that the supposed symbol of the "Cult of the Cave Bear" was found. This consisted of the skull of a three-year-old bear pierced in the cheek by the leg-bone of younger bear. The arrangement of these bones of different bears are not believed to have happened by chance.

A similar phenomenon was encountered in Regourdou, southern France. A rectangular pit contained the remains of at least twenty bears, covered by a massive stone slab. The remains of a Neanderthal lay nearby in another stone pit, with various objects, including a bear humerus, a scraper, a core, and some flakes, which were interpreted as grave offerings.

The unusual finding in a deep chamber of Basua Cave in Savona, Italy, is thought to be related to cave bear worship, as there is a vaguely zoomorphic stalagmite surrounded by clay pellets. It was apparently used by Neanderthals for a ceremony, the fact that bear bones lay scattered on the floor further suggested that this was likely to have had some sort of ritual purpose.^[29]

References

External links

• Show Caves of Romania