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?
***
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
***
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)
***
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 19th 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
****
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
****
-bear dentition, more to crushing than shearing,
record of brown bears in Atlas Mtns of
Africa in modern times
*****
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
*****
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
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