Large Mammals and Extinction U10110004 曾宣夢

Content 1.The Pleistocene Extinction 2.Why large mammals become extinct? 3.Climate change hypothesis 4.Hunting hypothesis 5.Two hypotheses chart 6.Conclusion 7.source

The Pleistocene Extinction Paleontologists the world over know that something catastrophic happened to the large mammals roaming the world during the Pleistocene Epoch.

mammoths mastodons saber-toothed cats woolly rhinos

In fact, well over 200 entire species giant ground sloths giant beavers In fact, well over 200 entire species (involving millions of individual animals) totally disappeared at the end of the Pleistocene some 10,000-12,000 years ago.

Why large mammals become extinct? Scientists remain puzzled about the reasons for this recent wave of extinctions that targeted large animals.

Why large mammals become extinct? Paleontologists believe that the causes of climate change, or human hunting. Major Long-term Cold Periods Over the Last 1/2 Billion Years (shown in blue) These time ranges are approximations and do not reflect the fact that temperature changes between major cold and warm phases of the earth's history usually occurred over long periods of time and that the cold periods varied in temperature and were not consistently cool.

Climate change hypothesis Having survived several major glacial advances ,and interglacial periods it is difficult to ascribe extinctions of these animals to climate change. Extent of major glaciers at the height of the last ice age (20,000 b.p.) (27% of the earth's land surfaces were covered by ice at that time)

Climate change hypothesis Ice age conditions in the northern   hemisphere during the Pleistocene (persistent glaciers with tundra and cold forests at lower elevations farther south)

Climate change hypothesis Warm period between glacial, a large amount of ice melted, a great flood occurred. Terrestrial and marine animal encounter great difficulties.

Why Earth's climate such a dramatic change, scientists have a lot of different theories, but how exactly reasons still uncertain.

Some scientists hypothesize that early humans hastened the decline Hunting hypothesis Some scientists hypothesize that early humans hastened the decline of these mammals by selectively hunting large forms. In Australia, is related to human. However, in North America is related to climate.

Two hypotheses chart (1) climate change hypothesis. (2) climate change and hunting Pleistocene Extinction Model (PEM) simulation results for Exogenous Climate Change (13.5%), Overkill Plus Exogenous Climate Change, and Second Order Predation plus Exogenous Climate Change.

Conclusion Human evolution was very likely affected strongly by the dramatic climate swings of the Pleistocene. These changes no doubt presented powerful new natural selection pressures. Many animal species were driven to extinction by the advancing and retreating ice ages. Humanity survived primarily by becoming more intelligent and adaptable. This allowed us to develop new cultural technology to deal with cold environments and changing food sources, especially during the last 1/4 million years.

Conclusion One of the greatest problems in the cold regions would have been the relative scarcity of plant foods that humans could eat during the winters. In response to this, our ancestors became more proficient at hunting animals, especially large ones that provided more calories. This required inventing more sophisticated hunting skills as well as better weapons and butchering tools. These changes in subsistence pattern were essential for our survival.

source Website http://zh.wikipedia.org/wiki/%E7%AC%AC%E5%9B%9B%E7%B4%80%E6%BB%85%E7%B5%95%E4%BA%8B%E4%BB%B6 http://www.atlantisquest.com/Paleontology.html http://anthro.palomar.edu/homo/homo_3.htm Book Earth Science-thirteen edition Time-life's illustrated world of science

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