A mammoth is any species of the extinct genus Mammuthus, proboscideans commonly equipped with long, curved tusks and, in northern species, a covering of long hair. They lived from the Pliocene epoch (from around 5 million years ago) into the Holocene at about 4,500 years agoin Africa, Europe, Asia, and North America. They were members of the family Elephantidae which contains, along with mammoths, the two genera of modern elephants and their ancestors.

EVOLUTION
The earliest known proboscideans, the clade which contains the elephants, existed about 55 million years ago around the Tethys Sea area. The closest relatives of the Proboscidea are the sirenians and the hyraxes. The family Elephantidae is known to have existed six million years ago in Africa, and includes the living elephants and the mammoths. Among many now extinct clades, the mastodon is only a distant relative of the mammoths, and part of the separate Mammutidae family which diverged 25 million years before the mammoths evolved. The following cladogram shows the placement of the genus Mammuthus among other proboscideans, based on hyoid characteristics: Mammut (Mastodon), Gomphotherium, Stegodon, Loxodonta (African elephant), Elephas (Asian elephant), Mammuthus (Mammoth).

COMPARISON OF A WOOLLY MAMMOTH (L) AND AN AMERICAN MASTODON (R)
Since many remains of each species of mammoth are known from several localities, it is possible to reconstruct the evolutionary history of the genus through morphological studies. Mammoth species can be identified from the number of enamel ridges on their molars; the primitive species had few ridges, and the amount increased gradually as new species evolved and replaced the former ones. At the same time, the crowns of the teeth became longer, and the skulls become higher from top to bottom and shorter from the back to the front over time to accommodate this.

The first known members of the genus Mammuthus are the African species M. subplanifrons from the Pliocene and M. africanavus from the Pleistocene. The former is thought to be the ancestor of later forms. Mammoths entered Europe around 3 million years ago; the earliest known type has been named M. rumanus, which spread across Europe and China. Only its molars are known, which show it had 8-10 enamel ridges. A population evolved 12-14 ridges and split off from and replaced the earlier type, becoming M. meridionalis. In turn, this species was replaced by the steppe mammoth, M. trogontherii, with 18-20 ridges, which evolved in East Asia ca. 1 million years ago. Mammoths derived from M. trogontherii evolved molars with 26 ridges 200,000 years ago in Siberia, and became the woolly mammoth, M. Primigenius. The Columbian mammoth, M. columbi, also evolved from a population of M. trogontherii which had entered North America. A 2011 genetic study showed that two examined specimens of the Columbian mammoth were grouped within a subclade of woolly mammoths. This suggests that the two populations interbred and produced fertile offspring. It also suggested that a North American form known as “M. jeffersonii” may be a hybrid between the two species.

From 3 Ma to the late Pleistocene, mammoths in continental Eurasia has undergone a major transformation, including a shortening and heightening of the cranium and mandible, increase in molar hypsodonty index, increase in plate number, and thinning of dental enamel. Due to this drastic change in physical appearance, people started grouping European mammoths separately into distinguishable clusters:

1) Early Pleistocene Mammuthus meridionalis
2) Middle Pleistocene Mammuthus trogontherii
3) Late Pleistocene Mammuthus primigenius

There is speculation to how variation occurred within the three chronospecies. Deviations in environment, climate change, and migration have also played a role in the evolutionary process of the mammoths. Take M. primigenius for example, during their lifespan, wooly mammoths would have lived in opened grassland biomes. The cool steppe-tundra of the Northern Hemisphere was the ideal place for mammoths to thrive because of the resources it supplied. Of course, with the warmings during the ice age, climate would also change the landscape and what was available to the mammoths altered drastically.

ETYMOLOGY
The word mammoth was first used in Europe during the early 1600s, when referring to maimanto tusks discovered in Siberia.[10] Thomas Jefferson, who famously had a keen interest in paleontology, is partially responsible for transforming the word mammoth from a noun describing the prehistoric elephant to an adjective describing anything of surprisingly large size. The first recorded use of the word as an adjective was in a description of a large wheel of cheese (the “Cheshire Mammoth Cheese”) given to Jefferson in 1802.

DESCRIPTION
Like their modern relatives, mammoths were quite large. The largest known species reached heights in the region of 4 m (13 ft) at the shoulder and weights up to 8 tonnes (9 short tons), while exceptionally large males may have exceeded 12 tonnes (13 short tons). However, most species of mammoth were only about as large as a modern Asian elephant (which are about 2.5m to 3m high at the shoulder, and rarely exceeding 5.4 tonnes). Both sexes bore tusks. A first, small set appeared at about the age of six months and these were replaced at about 18 months by the permanent set. Growth of the permanent set was at a rate of about 1 to 6 inches (2.5 to 15 cm) per year.

Based on studies of their close relatives, the modern elephants, mammoths probably had a gestation period of 22 months, resulting in a single calf being born. Their social structure was probably the same as that of African and Asian elephants, with females living in herds headed by a matriarch, whilst bulls lived solitary lives or formed loose groups after sexual maturity.

Scientists discovered and studied the remainders of a mammoth calf and found that the fat in a mammoth plays a major role to the mammoth’s form and ability. One of the major roles of mammoth fat is their ability to store large amounts of nutrients to accommodate to the colder climate they live in. The fat also allowed the mammoths to increase their muscle mass, allowing the mammoths to fight against enemies and live longer.

[source : wikipedia.org]