探索发现-冰河纪动物Ice Age Survivors02

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Since there are more eyes, ears and noses to detect a stalking predator.
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In a nearby clearing a young calf has become trapped in quicksand.
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It is a scene that has been played throughout history
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and one which has provided us with our richest source of fossil remains.
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When predators like this coyote approach, they too can become trapped.
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Fossils obtained from scenarios like this
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have allowed us to reconstruct a
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remarkably detailed portrait of North America during the Ice Age.
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But there are many unanswered questions.
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What we do know is that about ten thousand years ago,
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global temperatures suddenly began to rise.
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As the earth grew warmer, open prairies turned to forest
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and plants that were once plentiful suddenly disappeared.
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Animals that relied on these plants
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were, in many cases, unable to adjust to the changes.
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At around the same time the first human hunters arrived in North America.
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With many species like the woolly
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mammoth already weakened by environmental changes,
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it didn't take much for human hunters to finish them off.
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North America would never again
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sustain such a diverse and plentiful mammal population.
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The plains of Africa.
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The vast diversity of animals here is a living reminder of the world
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as it was before the Ice Age extinctions.
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Africa's geographical position
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protected most of its animals from the Arctic cold
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permitting huge herds to migrate across its limitless terrain.
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Today, Africa is still the home of the
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world's most magnificent herds of large mammals.
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Elephants are the largest land mammals on earth.
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During the Ice Age, they enjoyed the boundless resources Africa provided.
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Although they managed to survive the
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climatic changes at the end of the Ice Age,
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some of their distant relatives were less fortunate.
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Mammoths migrated throughout the world.
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But when the glaciers retreated and their food supply disappeared,
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so did the mammoths.
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Like the mammoths,
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today's elephants travel in large herds over enormous tracts of land.
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They require huge amounts of food.
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Quantities that today's shrinking habitat can barely supply.
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Grasses, shrubs and the bark from trees make up most of their diet.
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They chew their food with huge block like teeth
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that re-grow as they wear down.
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In order to reach and manipulate food, elephants evolved trunks.
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Though powerful enough to lift a
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whole tree, the trunk is also acutely sensitive to smell and touch.
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Stripping bark from trees and shrubs
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enables elephants to utilize a food
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source other animals can neither reach nor digest.
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As they did during the Ice Age,
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elephants travel great distances in search of water sources
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capable of supplying each elephant with up to twenty gallons a day.
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Often following the same paths
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over time, elephant roads are carved through even the densest vegetation.
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Female elephants live in groups of two or three sisters and their infants.
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Mothers carry their young for twenty-two months
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and closely defend them through childhood.
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Elephant skin is highly sensitive so they bathe frequently
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followed by a powdering with dust to prevent parasites and disease.
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But dwindling food supplies and space
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still make it likely they will follow their Ice Age cousins into extinction.
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A group of African lion slumbers in the midday heat.
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They've not changed much over millions
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of years as they boast a design that has kept them on top of the food chain.
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But their distant Ice Age relative was not so lucky.
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During the Ice Age saber-tooth cats
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used six-inch serrated fangs to slash open their prey.
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But when their prey became extinct, so did the saber-tooth.
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Today's African lions retain the basic characteristics of their extinct relatives.
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But a tight social structure sets them
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apart from many of today's other cat species.
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Copulation serves a dual purpose as it also bonds members of the pride.
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Ovulation is induced by the act of mating
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and pairs may copulate up to thirty times a day.
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The male dismounts quickly since
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females sometimes become aggressive toward their partners.
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Litters average three or four cubs
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and enjoy a long period of parental care.
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Support comes from all the females in the group
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lending a nursery-like atmosphere to the pride.
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Communal suckling is rare among mammals.
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Lions are one of the few whose females
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will actually nurse offspring other than their own.
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Lions have the largest brains and are the most social of all cats.
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Two traits that today, as they did during the Ice Age,
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contribute immensely to their survival.
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Females do most of the hunting and will teach their young at an early age.
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Camouflage and stealth are the keys to a successful hunt.