2010年6月26日星期六

Mammoth






A mammoth is any species of the extinct genus Mammuthus. These proboscideans are members of Elephantidae, the family of elephants and mammoths, and close relatives of modern elephants. They were often equipped with long curved tusks and, in northern species, a covering of long hair. They lived from the Pliocene epoch from around 4.8 million to 4,500 years ago.The word mammoth comes from the Russian мамонт mamont, probably in turn from the Vogul (Mansi) language, mang ont, meaning "earth horn".

The woolly mammoth was the last species of the genus. Most populations of the woolly mammoth in North America and Eurasia, as well all the Columbian mammoths in North America, died out around the time of the last glacial retreat, as part of a mass extinction of megafauna in northern Eurasia and the Americas. Until recently, it was generally assumed that the last woolly mammoths vanished from Europe and southern Siberia about 10,000 BC, but new findings show that some were still present there about 8,000 BC. Only slightly later, the woolly mammoths also disappeared from continental northern Siberia.A small population survived on St. Paul Island, Alaska, up until 3,750 BC,and the small mammoths of Wrangel Island survived until 1,650 BC.

A definitive explanation for their mass extinction is yet to be agreed upon. The warming trend (Holocene) that occurred 12,000 years ago, accompanied by a glacial retreat and rising sea levels, has been suggested as a contributing factor. Forests replaced open woodlands and grasslands across the continent. The available habitat may have been reduced for some megafaunal species, such as the mammoth. However, such climate changes were nothing new; numerous very similar warming episodes had occurred previously within the ice age of the last several million years without producing comparable megafaunal extinctions, so climate alone is unlikely to have played a decisive role.The spread of advanced human hunters through northern Eurasia and the Americas around the time of the extinctions was a new development, and thus probably contributed significantly.

Whether the general mammoth population died out for climatic reasons or due to overhunting by humans is controversial. Another theory suggests that mammoths may have fallen victim to an infectious disease. A combination of climate change and hunting by humans has been suggested as the most likely explanation for their extinction.

Data derived from studies done on living elephants suggests human hunting was likely a strong contributing factor in the mammoth's final extinction[citation needed]. Homo erectus is known to have consumed mammoth meat as early as 1.8 million years ago.

However, the American Institute of Biological Sciences also notes that bones of dead elephants, left on the ground and subsequently trampled by other elephants, tend to bear marks resembling butchery marks, which have previously been misinterpreted as such by archaeologists[citation needed].

The survival of the dwarf mammoths on Russia's Wrangel Island was due to the island's very remote location and lack of inhabitants in the early Holocene period[citation needed]. The European discovery of the island (by American whalers) did not occur until the 1820s[citation needed]. A similar dwarfing occurred with the Pygmy Mammoth on the outer Channel Islands of California, but at an earlier period. Those animals were very likely killed by early Paleo-Native Americans, and habitat loss caused by a rising sea level that split Santa Rosae into the outer Channel Islands[citation needed].

Recent research indicates that mammoths survived in the Americas until 10,000 years ago. This conclusion is from research, by James Haile and Eske Willerslev of the University of Copenhagen, of sediments found in central Alaska, and reported in the Proceedings of the National Academy of Sciences.

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