Bear natural history

The Evolution of the Polar Bear, Ursus Maritimus Phipps

Bjorn Kurten 1964

-existed in Europe during last glaciation, beach deposits now below sea level

-polar has decreased in size, like many other animals, postglacial dwarfing

-some dental characteristics of recent origin, evolution happening now, carnassials have high, pointed cusps, different from other ursids, carnivore adaptation

-descent from Brown bears, middle Pleistocene

-ulna fossil is of similar size to Arcdotus, Ursus maritimus tyrannus, )late Pleistocene polar bear) early Wurm

-Ursus arctos and maritimus can produce fertile hybrids

-probably evolved from Asiatic/ Siberian brown bears

-once it invaded new habitat, subjected to strong selective pressure, rapid evolutionary change

-dental trend towards series of homodont cheek teeth, like other aquatic carnivores

Phylogenetic Relationships of North American Ursids Based on Analysis of Mitochondrial DNA

Gerald F. Shields and Thomas D. Kocher 1991

-black bears differ from polar bears by 7.69%

-black bears differ from brown bears by 6.98%

-polar bears differ from brown bears by 1.07%

-individual polar bears differ by .37%, individual brown bears by .36%

- polar bears and brown bears are .7% divergent

-black bears are 9.% divergent from polar and brown bears

-polar bears and brown bears are sister taxa (Admiralty Island)

-bigger divergence between some Asiatic and American brown bears than between American brown and polar bears, because of geographical distance from Bering land bridge

-A 2.0% per million year rate of change has been calculated for the mtDNA of primates, a similar rate calculated for geese. If this value is similar for the mtDNA of bears, black bears separated from brown and polar for about 3.8 million years, this value approaches the 4.4 million year estimate for the duration of the ursine radiation based on analysis of proteins via two-dimensional electrophoresis

Diet and Co-ecology of Pleistocene Short-Faced bears and Brown Bears in Eastern Beringia

Paul E Matheus 1995

-Pleistocene short-faced bears of Beringia were highly carnivorous while contemporaneous brown bears’ diets were highly variable

-short-faced bears foraged as scavengers of widely dispersed large mammal carcasses and were simultaneously designed for highly efficient locomotion and for intimidating other large carnivores

-this allowed Arcdotus to forage economically over a large home range and seek out, procure and defend carcasses form other large carnivores, wide ranging scavenging specialists

-this notion challenges/ refutes the idea that competition from brown bears was a significant factor in the extinction of Arcdotus and as a corollary, that the general adaptations of brown bears stood them well through the Pleistocene extinctions

-brown bears did not reach areas of North America south of the continental ice masses until about 12,000 years ago, so Arcdotus and browns co-existed for many millennia during the Wisconsin glacial age in eastern Beringia

-stable carbon and nitrogen isotopes are tools in interpreting paleo- diets, you can tell if they were eating marine diets, vegetation or meat

-short-faced bears appear to have retained control of meat resources, indicates they were the dominant species, competition was resolved by brown bears taking on an opportunistic diet of seasonally available vegetation supplemented by salmon and occasional terrestrial meat resources

-stable carbon and nitrogen isotopes reveal that Arcdotus was a strict carnivore in eastern Beringia

short-faced bears lost features beneficial for predation, strength of limbs for acceleration and handling prey, plus, the presence of other specialized predators in Beringia precluded much opportunity for another large predator, however the other large predators put lots of large mammal carcasses out there, creating a niche for Arcdotus as a scavenger, a niche which disappeared with the extinctions of many large prey and their predators

-Arcdotus’ limbs were designed for a super-efficient gate, not for high speed, it was relatively slender, not built for power and killing but for locomotor efficiency

-it’s extremely large size worked well for intimidation and domination of carcasses

-cranial anatomy and jaws imparted more power to the distal teeth, hence the short face, it could do some bone cracking

-the wide face also could indicate better olfactory capacity and the ability to wolf down large chunks of unchewed meat and bone, like the hyaena

-until Beringia could support enough of a varied ecosystem, Arcdotus could have prevented brown bears from entering more southerly regions of North America

-the ecological plasticity of brown bears and their ability to hibernate and avoid seasonal bottlenecks of food resources suggest two possible reasons they continue to survive in the new World while Tremarctine bears have all but disappeared.

Tremarctine bears don’t hibernate?

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Bear Den

-Of approx 4500 mammals, 231 are carnivores

-dogs, 35 species, racoons, 16 species, weasels, 67 species, mongoose, 66 species, hyaena, 4 species, cat 35 species, bear 8 species

black bears can weigh up to 500 pounds and overlap in size with smaller brown bears, largest so far was 805 pounds, can run 25 mph, curved claws adapted to tree climbing

-Kermode bear/ ghost bear: only found on three small isolated islands off BC, cream colored

range can be 10 - 40 sq miles, males have larger range, depends on availability of resources

-delayed implantation of embyro, if not enough fat reserves, embryo is reabsorbed

-can hibernate from four to seven months or not at all

Polar bears: most closely related to brown bears of Admiralty Island, there are 7 distinct populations, total population is between 20 and 40,000, 1967 treaty of Russia, Norway, Greenland, US and Canada to protect bears

-@ 3.5' tall and 8 - 11.5' long, females weigh @ 650, males 1000 - 1300 lbs. , record male 2200 lbs., forepaws 12" in diameter, stomachs can take 150 lbs. Of food, carnassials have moved back to more shearing shape, canines longer than browns

-can swim 60 miles without rest, can dive 15' and hold breath for 2 minutes, can leap out of water 6' to grab a seal

-when ice melts they are stranded on land and scavenge whatever

-individual bear may cover 100,000 square miles in it’s life, 25 years

-pregnant females the only ones to hibernate

Brown bears:

-can outrun a horse in short distance, 35 - 40 mph

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The Cave Bear Story    Life and Death of a Vanished Animal

Bjorn Kurten 1976

Evolution of bears of the Ursus line:

20 mya Ursavus

10 mya Protoursus evolves from Ursavus, Ursavus extinct

5 mya Ursus minimus

1.5 mya Ursus etruscus, split to Black bear lines

1 mya U. etruscus split to U. arctos

700,000 ya ancestors of cave bear

300,000 ya Polar bear, Ursus spelaeus (cave bear)

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Carnivore Behavior, Ecology and Evolution vol 2

John L. Gittleman ed, 1996

Biogeography of the Order Carnivora

Robert M. Hunt Jr.

Ursidae:

-Arcdotus is first ursid to reach S America, younger than 2 million ya, at least two species of S American Arcdotus

-Ursus enters N Africa in Pleistocene, U. arctos said to have disappeared from NW Africa in the mid 19^th century

-Tremarctini includes ancestral Plionarctos, first appearing 7 million years ago, in N America, confined to western N America, Tremarctos and Arcdotus are probable descendants, they were plantigrade, but Kurten believes they never evolved the turning in if the forefeet gate of ursini

-In N America, Tremarctos is first known at 2.5 mya and last recorded at 7 - 8000 ya

-Arcdotus and Tremarctos, the only ursids to reach S America, Arcdotus known from fossils, Tremarctos is known only from the living Tremarctos ornatus/ spectacled bear, from mountainous regions of NW S America

-why tremarctine bears made it to S America and other ursids not is an enigma

-Arcdotus, at 250 - 630 kg, the largest land carnivorans to ever live, Andrewsarchus was not Carnivora, more like artiodactyl

-Arcdotus appears in N America, all over N America, in late Pleistocene, last known from @ 12,000 ya

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Giant Short-Faced Bear

Ronald L. Richards, William D. Turnbull

in Fieldiana, Geology, New Series No. 30   4/ 28/95

-two subspecies? a smaller A. simus simus and the larger A. simus yukonensis

-known from more than 100 localities in N America

-a shortened face with somewhat crowded cheek teeth compared to Black bear, carnassials are more like dogs than bears, about the same size as Kodiak bears, strongly sexually dimorphic

good drawings

-carnassials of Arcdotus simus more like dogs than bears, more like a true carnivore, 30 bears represented, short faced bear ranged from Yukon to PA, Kentucky, TX, CA, they or their close relatives were widely distributed in S America in the Pleistocene, it’s more closely related to the spectacled bear of the Andes than to any living N American type, modern bears were outnumbered by Arcdotus

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-bear dentition, more to crushing than shearing, record of  brown bears in Atlas Mtns of Africa in modern times

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Carnivore behavior, Ecology and Evolution vol 2

John L. Gittleman, ed 1996

Demographic and Historical Effects on Genetic Variation of Carnivores

Robert K. Wayne, Claus Peter Koepfi

-ursids: the extent of genetic divergence between Russian and Romanian brown bears, as a group and old world brown bears, as a group is greater than that between polar bears and N American brown bears, the latter two species likely diverged only in the late Pleistocene

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The Walking Larder   Patterns of Domestication, pastoralism, and predation

Juliet Clutton-Brock

-Martin’s 1967 overkill hypothesis, upgraded 1973, 1984

-humans entered N America 12 - 13,000 ya, colonized all of N America by 11,000 ya and S America by 10,000 ya, blitzkrieg on Rancholabrean megafauna

-however, case can be made that humans could not enter N America because of the mega carnivores and only after they started to collapse could they come in

-Siberian fauna made up of cold climate generalists, Rancholabrean fauna was densely packed, specialists, large bodies, A simus, Panthera atrox, Smilodon fatalis, C dirus

-if humans have historically had problems handling the smaller grizzlies, how could they have handled A simus with no trees to climb?

-various Siberian species appear in Alaska in early Pleistocene, but do not colonize lower N America until Rancholabrean fauna begin to collapse

-human hunters, after successful entry, hastened extinction of remnants of RL fauna

-elephants killed by Paleo-Indians were small, less food

-also, some extinction preceded arrival by humans

-upper paleolithic expansion of people, 40 - 30,000 ya, they may have knocked on the door but not got in far, could have come in boats, but why didn’t they then kill off the dwarf mammoths on Channel Islands?

-11,100 ya, Lubbock Lake, TX,  Arcdotus remains with cut marks along with human remains, they did co-exist in lower N America, domestic dog was present, dog could have helped keep them at bay, (good drawing comparing simus with grizzly)

-humans entered lower N America from Beringia/ Siberia along with brown bears, moose, caribou, wolverine, probably along with elk and extant bison (a Holocene dwarf)

-wolf came in at this time too, may have colonized along glacial margins in late glacial times, expanded roughly with the demise of Dire wolf

-brown bears were in Alaska in the Wisconsin, but not in lower N America, in Alaska browns concurrent with A simus, (different niches, simus not found in glaciated areas), post-glacially, browns occupy range once held by simus

-Alaskan fauna does contain a good number of typical RL fauna

-on Siberian side of Beringia, upper Paleolithic people appear at 14,000 ya and shortly thereafter in America

-human anti-predator strategies: climb a tree, throw rocks, fire, but how did they do it without trees? thorn covered nest, stabbing spears, threat calls

-current safety in wild depends on killing man-eaters, so that habit of eating people cannot be passed on, if food habits are initiated as a tradition, then stopping the tradition is important to human safety, upper limit of ability to kill carnivores may be with browns and polar bears, providing sufficient dogs were at hand, Masai kill lions with just a spear

-in pristine N America, grizzlies very common west of Mississippi, in season, along rivers, with drowned  bison and elk carcasses, explorers saw 220 bears in one day, killed 8 which attacked and two more at night in camp

-travelers in CA saw 30 - 50 bears per day, Indians were chewed up and deformed from bear attacks, CA Indians avoided good bear habitat, CA was sparsely settled by Indians, Indians liked that Spanish could kill the bears and rapidly colonized areas cleared of bears

-central valley of CA had all the resource characteristics for an advanced civilization, yet Spanish found low native population and many large bears

-bears generally avoided people except if with cubs, wounded, starving old, brown bear gives every indication of willingness to avoid and learn, it had been second fiddle to cave bear and A. simus

-to spear a bear in the heart from the front: would hit 90% bone, 50% bone from the side, grizzlies wounded with lances can still kick ass, Spanish lanced them and bears still killed horses and people, they die slowly, some took 10 shots and didn’t die for half an hour

- a group of men, with large dogs and stout, broad lances could kill one with reduced risk, Eskimos did the same with polar bears but considered it very dangerous

-European Paleolithic hunters stayed away from cave bears, Kurtén

A. simus was a foot taller at the shoulder than CA grizzly, was carnivorous, functioning carnassials, don’t find brown and black bears in natural traps but do find simus

Arcdotus excluded grizzlies except in the coldest periglacial regions, grizzly could not outclimb Arcdotus in areas with few trees and neither could people

-no evidence for broad lances in late glacial record, narrow-bladed spears would have been ineffective, dogs could have helped

-predation on RL fauna was heavy by specialized, large carnivores, Siberian hunters moving south would perhaps have found these predators an insurmountable foe