Mammoth

Mammoths lived during the Ice Ages of the Pleistocene epoch. The oldest recovered mammothfossils, found in Africa, are four million years old. Mammoths migrated from Africa, and several species of varying sizes and appearances evolved on other continents. Some mammoths crossed the Bering land bridge. Most mammoths favored tundra habitats formed when Ice Age glaciers covered parts of the northern hemisphere.

Anatomy
Most mammoths were large mammals, standing 3.5 to 4.3 meters (12 to 14 feet) tall when measured from the ground to the top of their shoulders. They weighed an average of seven metric tons (eight tons). Other mammoths were dwarves that only stood 1.8 meters (6 feet) tall. These small mammoths lived on islands, including Siberia's Wrangel Island and California's Channel Islands. Woolly mammoths grew long, thick brown fur over a short undercoat, which protected them in cold climates. Fat layers, which were 7.5 centimeters (3 inches) thick, underneath their skin and in their shoulder hump and prominent brow, insulated their bodies. Each mammoth had two ivory tusks, which extended fromtheir upper jaw. Mammoths' tusks were as long as five meters (sixteen feet) and curved toward and crossed over their trunk. During their lifespan, they had a total of twenty-four molars, which they shed. Because of their cold habitat, mammoths' ears were small, to retain heat.

Life Cycle
Mammoths roamed in herds, sometimes covering great distances in their search for vegetation, such as sedge and Arctic sagebrush, to eat. They spent an average of twenty hours a day finding and eating food. Chewing plants smoothed their teeth. When frozen land inhibited plant growth, the mammoths' stored fat provided essential nutrients and vitamins necessary to live. Mammoths acted protectively toward immature, elderly, and infirm herd members. Males often fought over females during breeding seasons. Gestation lasted twenty-two months. Females usually produced one calf. Mammoths were unique because their mammary glands were near their front legs, unlike other mammals. Young mammoths remained with their mothers for several years, gradually becoming independent. Mammoths reached maturity by the age of twelve years. Because of their size, adult mammoths had few predators. They moved slowly, which made them more vulnerable. The saber-tooth tiger killedmammoths for their flesh, and prehistoric humans hunted mammoths for their meat, hides, bones, and tusks. Human hunters devised strategies to capture mammoths in traps that confined their legs. Prehistoric people used mammoth tusks and bones to build shelters. Many mammoths died when they fell into naturally occurring sinkholes or were mired by quicksand and tarpits. Sometimes, male mammoths' tusks became entangled while fighting, and they starved to death. Although mammoths were abundant during the Ice Ages, they became extinct in the period between 13,000 and 2000 b.c.e. Paleontologists estimate that the last mammoths died circa 1800 b.c.e. Researchers hypothesize that mammoths' extinction occurred because they were unable to adapt to the altered environment, specifically the warmer climate and different edible plants that existed after the final Ice Age, or that humans hunted them into extinction. Evidence exists for both theories. Mammoths migrated north as glaciers began to recede. When the final Ice Age glaciers disappeared about 9500 b.c.e., many placental mammals became extinct. Fossils suggest that some mammoths survived on an isolated Siberian Arctic island until 1500 b.c.e.

Recovering Specimens
Humans have found mammoth fossils on land and in bodies of water, such as the North Sea, which used to be dry land where mammoths roamed. The Siberian permafrost has preserved carcasses that have not decomposed or become too dry for examination. A baby mammoth that scientists called Dima was located in 1977 and had intact red blood cells. Many mammoth fossils have been located during the digging of the Eastside Reservoir, near Los Angeles, California, including a female found in April, 1999, which is considered to be the best preserved mammoth specimen. In 2000, paleontologists recovered what they believed to be the first completely frozen mammoth on Siberia's Taimyr Peninsula. Named the Jarkov mammoth, it was airlifted to a cold cave research facility, encased in a block of permafrost that included plants, insects, and pathogens, which scientists hoped would provide insights to mammoths' environments. They planned to test a hypothesis that mammoths became extinct due to an epidemic. Initially, scientists hoped to secure enough DNA to clone the mammoth, but it turned out that radar readings had incorrectly shown more of the carcass remaining than actually existed