Mammoth
Temporal range: Late Miocene to Late Holocene, 6.2–0.0037 Ma
Columbian mammoth in the Page Museum in Los Angeles.
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Proboscidea
Family: Elephantidae
Subfamily: Elephantinae
Tribe: Elephantini
Genus: Mammuthus
Brookes, 1828
Type species
Elephas primigenius[1][2]
Species
Synonyms
  • Archidiskodon Pohling, 1888
  • Parelephas Osborn, 1924
  • Mammonteus

A mammoth is any species of the extinct elephantid genus Mammuthus. The various species of mammoth were commonly equipped with long, curved tusks. They lived from the late Miocene epoch (from around 6.2 million years ago) into the Holocene about 4,000 years ago, and various species existed in Africa, Europe, Asia, and North America. Mammoths are more closely related to living Asian elephants than African elephants.

The oldest mammoth representative, Mammuthus subplanifrons, appeared around 6 million years ago during the late Miocene in what is now southern and Eastern Africa.[3] Later in the Pliocene, by about three million years ago, mammoths dispersed into Eurasia, eventually covering most of Eurasia before migrating into North America around 1.5–1.3 million years ago, becoming ancestral to the Columbian mammoth (M. columbi). The last species to emerge, the woolly mammoth (M. primigenius), evolved about 700-400,000 years ago in Siberia, with some surviving on Russia's Wrangel Island in the Arctic Ocean until as recently as roughly 3,700 to 4,000 years ago, still extant during the existence of the earliest civilisations in ancient Egypt and Mesopotamia.

Etymology and early observations

The word mammoth was first used in Europe during the early 17th century, when referring to maimanto tusks discovered in Siberia.[4] John Bell,[5] who was on the Ob River in 1722, said that mammoth tusks were well known in the area. They were called "mammon's horn" and were often found in washed-out river banks. Some local people claimed to have seen a living mammoth, but they came out only at night and always disappeared under water when detected. He bought one and presented it to Hans Sloan who pronounced it an elephant's tooth.

The folklore of some native peoples of Siberia, who would routinely find mammoth bones, and sometimes frozen mammoth bodies, in eroding river banks, had various interesting explanations for these finds. Among the Khanty people of the Irtysh River basin, a belief existed that the mammoth was some kind of a water spirit. According to other Khanty, the mammoth was a creature that lived underground, burrowing its tunnels as it went, and would die if it accidentally came to the surface.[6] The concept of the mammoth as an underground creature was known to the Chinese, who received some mammoth ivory from the Siberian natives; accordingly, the creature was known in China as yǐn shǔ 隐鼠, "the hidden rodent".[7]

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.[8]

Evolution

The earliest known proboscideans, the clade that 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.[9]

The following cladogram shows the placement of the genus Mammuthus among other proboscideans, based on hyoid characteristics and genetics:[10][11]

Elephantimorpha

Mammutidae (mastodons)

Elephantida

Gomphotheriidae (gomphotheres)

Elephantoidea

Stegodontidae (stegodontids)

Elephantidae

Loxodonta (African elephants)

Palaeoloxodon (straight-tusked elephants)

Elephas (Asian elephants)

Mammuthus (mammoths)

Comparison of a woolly mammoth (left) and an American mastodon (right).

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/lamellae 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 became higher from top to bottom and shorter from the back to the front over time to accommodate this.[12]

The earliest mammoths, assigned to the species Mammuthus subplanifrons, are known from southern and eastern Africa, with the earliest records dating to the Late Miocene, around 6.2–5.3 million years ago.[3] By the Late Pliocene, mammoths had become confined to the northern portions of the African continent with remains from this time assigned to Mammuthus africanavus.[13] During the Late Pliocene, by 3.2 million years ago, mammoths dispersed into Eurasia via the Sinai Peninsula. The earliest mammoths in Eurasia are assigned to the species Mammuthus rumanus.[14] The youngest remains of mammoths in Africa are from Aïn Boucherit, Algeria dating to the Early Pleistocene, around 2.3–2 million years ago (with a possible later record from Aïn Hanech, Algeria, dating to 1.95–1.78 million years ago).[13]

Mammuthus rumanus is thought to be the ancestor of Mammuthus meridionalis, which first appeared at the beginning of the Pleistocene, around 2.6 million years ago.[15] Mammuthus meridionalis subsequently gave rise to Mammuthus trogontherii (the steppe mammoth) in Eastern Asia around 1.7 million years ago. Around 1.5–1.3 million years ago, M. trogontherii crossed the Bering Land Bridge into North America, becoming ancestral to Mammuthus columbi (the Columbian mammoth).[16] At the end of the Early Pleistocene Mammuthus trogontherii migrated into Europe, replacing M. meridionalis around 1–0.8 million years ago.[15] Mammuthus primigenius (the woolly mammoth) had evolved from M. trogontherii in Siberia by around 600,000–500,000 years ago, replacing M. trogontherii in Europe by around 200,000 years ago, and migrating into North America during the Late Pleistocene.[17]

A number of dwarf mammoth species evolved on islands with a small body size as a result of insular dwarfism. These include Mammuthus lamarmorai on Sardinia (late Middle-Late Pleistocene),[18] Mammuthus exilis on the Channel Islands of California (Late Pleistocene),[19] and Mammuthus creticus on Crete (Early Pleistocene).[20]

Description

Restoration of a steppe mammoth

Like living elephants, mammoths typically had large body sizes. The largest known species like Mammuthus trogontherii (the steppe mammoth) were considerably larger than modern elephants, reaching heights in the region of 4 m (13.1 ft) at the shoulder and weights of 11 tonnes (12 short tons), while exceptionally large males may have reached 4.5 m (14.8 ft) at the shoulder and 14.3 tonnes (15.8 short tons) in weight.[21] However, woolly mammoths were considerably smaller, only about as large as modern Asian elephants and African bush elephants at about 2.3 m to 3.15 m high at the shoulder, and 2.8 to 6 tonnes in weight on average).[21][22] The insular dwarf mammoth species were considerably smaller, with the smallest species M. creticus estimated to have a shoulder height of only around 1 metre (3.3 ft) and a weight of about 180 kilograms (400 lb), making it one of the smallest elephantids known.[21]

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 2.5 to 15.2 cm (1 to 6 in) per year.[23] The tusks display a strong spiral twisting.[24] Mammoth tusks are among the largest known among proboscideans with some specimens over 4 m (13.1 ft) in length and likely 200 kg (440.9 lb) in weight with some historical reports suggesting tusks of Columbian mammoths could reach lengths of around 5 m (16.4 ft) substantially surpassing the largest known modern elephant tusks.[25]

The number of lamellae (ridge-like structures) on the molars, particularly on the third molars, substantially increased over the course of mammoth evolution. The earliest Eurasian species M. rumanus have around 8-10 ridges on the third molars,[26] while Late Pleistocene woolly mammoths have 20-28 lamellae on the third molars. These changes also corresponded with reduced enamel thickness and increasing tooth height (hypsodonty).[27] These changes are thought to be adaptations to increased abrasion as a result of increasing adaptation of the mammoth lineage from a browsing based diet in M. rumanus, towards a grazing diet in later species.[28][29]

While early mammoth species like M. meridionalis were probably relatively hairless, similar to modern elephants,[30] M. primigenius and likely M. trogontherii had a substantial coat of fur, among other physiological adaptations for living in cold environments. Genetic sequencing of M. trogontherii-like mammoths, over 1 million years old from Siberia suggests that they had already developed many of the genetic changes found in woolly mammoths responsible for tolerance of cold conditions.[31] Scientists discovered and studied the remains of a mammoth calf, and found that fat greatly influenced its form, and enabled it to store large amounts of nutrients necessary for survival in temperatures as low as −50 °C (−58 °F).[32] The fat also allowed the mammoths to increase their muscle mass, allowing the mammoths to fight against enemies and live longer.[33] Woolly mammoths evolved a suite of adaptations for arctic life, including morphological traits such as small ears and tails to minimize heat loss, a thick layer of subcutaneous fat, and numerous sebaceous glands for insulation, as well as a large brown-fat hump like deposit behind the neck that may have functioned as a heat source and fat reservoir during winter.[34]

Size of various mammoth species compared with a human

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,[35] with adult males experiencing periods of musth.[36]

Diet

The earliest mammoth species like M. subplanifrons and M. rumanus were mixed feeders (both browsing and grazing) to browsers. Over the course of mammoth evolution in Eurasia, their diet shifted towards mixed feeding-grazing in M. trogontherii culminating in the woolly mammoth, which was largely a grazer, with stomach contents of woolly mammoths suggesting that they largely fed on grass and forbs. M. columbi is thought to have been a mixed feeder.[29]

Relationship with early humans

Paleolithic painting of mammoth from the Rouffignac Cave

Evidence that humans interacted with mammoths extends back to around 1.8 million years ago, with a number of bones of Mammuthus meridionalis from the Dmanisi site in Georgia having marks suggested to the result of butchery by archaic humans, likely as a result of scavenging.[37] During the Last Glacial Period, modern humans hunted woolly mammoths,[38] used their remains to create art and tools,[39][38] and depicted them in works of art.[39] A possible engraving of M. columbi is known from Vero Beach, Florida.[40]

Extinction

Main articles: Woolly mammoth § Extinction, and Columbian mammoth § Extinction

Towards the end of the Last Glacial Period, the range of the woolly mammoth began to contract. By the Younger Dryas (around 12,900-11,700 years Before Present), woolly mammoths were confined to the northernmost regions of Siberia. This contraction is suggested to have been caused by the warming induced expansion of forests, which were unfavourable habitats, with the possible additional pressure of human hunting. The last woolly mammoths in mainland Siberia became extinct around 10,000 years ago, during the early Holocene.[41] Relict populations survived on Saint Paul island in the Bering Strait until around 5,600 years ago, likely due to the degradation of freshwater sources,[42] and on Wrangel Island off the coast of Northeast Siberia until around 4,000 years ago.[41] The last reliable dates of the Columbian mammoth date to around 12,500 years ago.[43] Columbian mammoths became extinct as part of a wave extinctions of most large mammals across the Americas. Remains of Columbian mammoths have been found at a number of sites with tools and cut marks suggesting that they were hunted by recently arrived Paleoindians, which may have been a contributory factor in their extinction.[44]

See also

References

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Further reading