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Columbian mammoth

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Columbian mammoth
Temporal range: Late Pleistocene to Early Holocene, 0.013–0.011Ma
Columbian mammoth.JPG
Composite male skeleton in the Page Museum at the La Brea Tar Pits, Los Angeles
Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Proboscidea
Family: Elephantidae
Genus: Mammuthus
Species: M. columbi
Binomial name
Mammuthus columbi
(Falconer, 1857)
Synonyms

The Columbian mammoth (Mammuthus columbi) was a species of mammoth that inhabited North America as far north as the northern United States and as far south as Costa Rica during the Pleistocene epoch. It was one of the last in a line of mammoth species, beginning with M. subplanifrons in the early Pliocene. The Columbian mammoth evolved from the steppe mammoth, which entered North America about 1.5 million years ago. The pygmy mammoths of the Channel Islands evolved from Columbian mammoths. The closest extant relative of the Columbian mammoths is the Asian elephant.

Reaching 4 m (13 ft) at the shoulders and 10 tonnes (20,000 lb) in weight, the Columbian mammoth was one of the largest species of mammoth. It had long, curved tusks and four molars, which were replaced six times during the lifetime of an individual. It most likely used its tusks and trunk like modern elephants—for manipulating objects, fighting, and foraging. Bones, hair, dung and stomach contents have been discovered, but no preserved carcasses are known. The Columbian mammoth preferred open areas, such as parkland landscapes, and fed on sedge, grass, and other plants. It did not live in the Arctic regions of Canada, which were instead inhabited by woolly mammoths. The ranges of the two species may have overlapped, and genetic evidence suggests that they interbred. Several sites contain the skeletons of multiple Columbian mammoths, either as the result of single incidents such as flash floods or natural traps in which individuals accumulated over time.

Columbian mammoths coexisted with Palaeoamericans, who hunted them for food, used their bones for making tools, and depicted them in ancient art. Columbian mammoth remains have been found in association with Clovis culture artefacts; these remains may have stemmed either from hunting or from scavenging. The Columbian mammoth disappeared at the end of the Pleistocene around 11,000 years ago, most likely as a result of habitat loss caused by climate change, hunting by humans, or a combination of both.

Taxonomy[edit]

Lithograph depicting the holotype molar (specimen BMNH 40769), 1863

The Columbian mammoth was first scientifically described by Scottish naturalist Hugh Falconer in 1857, who named the species Elephas columbi, after Christopher Columbus. The animal had been brought to Falconer's attention by Charles Lyell in 1846, who had sent him some fragmentary molars found during the 1838 excavation of the Brunswick Altamaha Canal in Georgia, in the southeastern United States. At the time, similar fossils from across North America were attributed to woolly mammoths (then Elephas primigenius). Falconer, however, found his specimens to be distinct, a conclusion he confirmed by examining their internal structure and studying additional molars from Mexico. William Phipps Blake and Richard Owen claimed their newer name E. texianus was more appropriate for the species, but this was rejected by Falconer. Falconer also suggested that E. imperator and E. jacksoni, two other American elephants described from molars, were based on too fragmentary remains to be properly classified.[1] More complete material that may be from the same quarry as Falconer's fragmentary holotype molar was reported in 2012, and could help shed more light on that specimen, since doubt about its adequacy as a holotype has been raised.[2]

In the early 20th century, the taxonomy of extinct elephants became increasingly complicated. In 1942, Henry Fairfield Osborn's posthumous monograph on the Proboscidea was published, wherein he used various genus and subgenus names that had previously been proposed for extinct elephant species, such as Archidiskodon, Metarchidiskodon, Parelephas, and Mammonteus. Osborn also retained names for many regional and intermediate subspecies or "varieties", and created recombinations such as Parelephas columbi felicis and Archidiskodon imperator maibeni.[3] The taxonomic situation was simplified by various researchers from the 1970s onwards: all species of mammoth were retained in the genus Mammuthus, and many proposed differences between species were instead interpreted as intraspecific variation.[4] In 2003, palaeontologist Larry Agenbroad summarised current views about North American mammoth taxonomy, and concluded that several species had been declared junior synonyms, and that M. columbi (the Columbian mammoth) and M. exilis (the pygmy mammoth) were the only species of mammoth endemic to the Americas (as other species lived both there and in Eurasia). The idea that species such as M. imperator (the imperial mammoth) and M. jeffersoni (Jefferson's mammoth) were either more primitive or advanced stages in Columbian mammoth evolution was largely dismissed, and they were regarded as synonyms. In spite of these conclusions, Agenbroad cautioned that American mammoth taxonomy is not yet fully resolved.[5]

Evolution[edit]

The adult male "Aucilla mammoth" specimen, Florida Museum of Natural History

The earliest known members of Proboscidea, the clade that contains the elephants, existed about 55 million years ago around the Tethys Sea area. The closest living relatives of the Proboscidea are the sirenians (dugongs and manatees) and the hyraxes (an order of small, herbivorous mammals). The family Elephantidae existed six million years ago in Africa, and includes the living elephants and the mammoths. Among many now extinct clades, the mastodon (Mammut) is only a distant relative, and part of the distinct family Mammutidae, which diverged 25 million years before the mammoths evolved.[6] The Asian elephant (Elephas maximus) is their closest extant relative. The following cladogram shows the placement of the Columbian mammoth among other proboscideans, based on characteristics of the hyoid bone in the neck:[7]




Mammut americanum (American mastodon)




Gomphotherium sp.




Stegodon zdanskyi




Loxodonta africana (African elephant)




Elephas maximus (Asian elephant)



Mammuthus columbi (Columbian mammoth)








Excavation of a pygmy mammoth, which evolved from Columbian mammoths on the Channel Islands

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 (or lamellar plates) on their molars: primitive species had few ridges, and the number increased gradually as new species evolved to feed on more abrasive food items. The crowns of the teeth became deeper in height and the skulls became taller to accommodate this. At the same time, the skulls became shorter from front to back to minimise the weight of the head.[8][9] The short, tall skulls of woolly and Columbian mammoths are the culmination of this process.[6]

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 European mammoth has been named M. rumanus; it spread across Europe and China. Only its molars are known, which show that it had 8–10 enamel ridges. A population evolved 12–14 ridges, splitting off from and replacing the earlier type, becoming M. meridionalis about 2–1.7 million years ago. In turn, this species was replaced by the steppe mammoth (M. trogontherii) with 18–20 ridges, which evolved in eastern Asia around 2-1.5 million years ago.[8] The Columbian mammoth evolved from a population of M. trogontherii (formerly thought to have been M. meridionalis) that had crossed the Bering Strait and entered North America about 1.5 million years ago; it retained a similar number of molar ridges. Mammoths derived from M. trogontherii evolved molars with 26 ridges 400,000 years ago in Siberia and became the woolly mammoth (M. primigenius). Woolly mammoths entered North America about 100,000 years ago.[6]

Specimen sometimes assigned to M. jeffersonii, a possible hybrid between Columbian and woolly mammoths, American Museum of Natural History

A population of Columbian mammoths that lived between 80,000 and 13,000 years ago on the Channel Islands of California, 10 km (6 miles) away from the mainland, evolved to be less than half the size of the mainland Columbian mammoths, likely due to food scarcity. They are therefore considered the distinct species M. exilis, the pygmy mammoth (or a subspecies, M. c. exilis). Bones of larger specimens have also been found on the islands, but it is unknown whether these were stages in the dwarfing process, or later arrivals of Columbian mammoths.[10][7][11]

A 2011 study of the complete mitochondrial genome (inherited through the female line) of the Columbian mammoth showed that the two examined specimens, including the morphologically typical "Huntington mammoth", were grouped within a subclade of woolly mammoths. This suggests that the two populations interbred and produced fertile offspring, but it is unknown whether the results mean that a Columbian mammoth haplogroup had been introduced to the woolly mammoths through introgression and dominated that species, or the other way around. The latter scenario is similar to behaviour seen in modern species of African elephant (Loxodonta), the African bush elephant (L. africana) and the African forest elephant (L. cyclotis). The males of the former species are larger, and therefore out-compete males of the smaller species. The same behaviour may have occurred between the larger Columbian and smaller woolly mammoths, and the authors of the study also suggested that the North American form sometimes referred to as M. jeffersonii may have been a hybrid between the two species, as it is morphologically intermediate.[12] These findings were not expected by scientists, nuclear DNA and more specimens will have to be analysed to clarify the situation.[13]

Description[edit]

Restoration by Charles R. Knight, 1909

The Columbian mammoth reached 4 m (13 ft) tall at the shoulder, and it weighed up to 10 tonnes (20,000 lb, as much as 130 adult humans). It was larger than the modern African elephant and the woolly mammoth, which both reach about 2.7 to 3.4 m (9–11 ft), and about the same size as the earlier mammoth species M. meridionalis and M. trogontherii. Males were generally larger and more robust, while females were smaller and more lightly built. The best indication of sex is the size of the pelvic girdle, as the birth canal is always wider in females than in males. Like other mammoths, the Columbian mammoth had a high, single-domed head and a sloping back with a high shoulder hump; this shape resulted from the spinous processes (protrusions) of the back vertebrae decreasing in length from front to rear. Juveniles, on the other hand, had convex backs like Asian elephants.[14] Other skeletal features include a rostrum (beaklike structure) that was short and deep, a rounded mandibular symphysis (central jaw ridge), and the coronoid process of the mandible (upper protrusion of the jaw bone) extending above the molar surfaces.[15]

Size (blue) compared to a human and other proboscideans

Apart from their larger size and more primitive molars, Columbian mammoths also differed from woolly mammoths by the mandibular symphysis being more downturned, and the dental alveoli of the tusks being directed laterally, more away from the midline.[12] The tail of the Columbian mammoth was intermediate in length between that of modern elephants and the woolly mammoth. Soft tissue of the Columbian mammoth has not been found, so much less is known about its appearance than that of the woolly mammoth. They lived in warmer habitats than the woolly mammoth, so they probably lacked many of the adaptations seen in that species. Hair thought to have belonged to the Columbian mammoth has been discovered in the Bechan Cave, Utah, where mammoth dung has also been found. Some of this hair is coarse, and identical to that known to belong to woolly mammoths. Since this location is so far south, it is unlikely that the hair belonged to woolly mammoths. The distribution and density of this fur on the living animal is unknown, but it was probably less dense than that of the woolly mammoth, due to the warmer habitat.[6][14]

Dentition[edit]

Mandible and lower molars, Palaeontological Museum in Tocuila, Mexico

Columbian mammoths had very long tusks, which were more curved than those of modern elephants. The largest known mammoth tusk belonged to a Columbian mammoth and is 4.9 metres (16 ft) long. Others range between 3.5 metres (11 ft) and 4.121 metres (13.52 ft) long, and Columbian mammoth tusks were usually not much larger than those of woolly mammoths, which reached 4.2 metres (14 ft). The tusks of females were much smaller and thinner. About a quarter of the length was inside the sockets. The tusks grew spirally in opposite directions from the base and continued in a curve until the tips pointed towards each other, sometimes crossing. In this way, most of the weight would have been close to the skull, and there would be less torque than with straight tusks. The tusks were usually asymmetrical and showed considerable variation, with some tusks curving down instead of outwards and some being shorter due to breakage. Columbian mammoth tusks were generally less twisted than those of woolly mammoths. Calves developed small milk tusks a few centimetres long at six months old, which were replaced by permanent tusks a year later. Tusk growth continued throughout life but became slower as the animal reached adulthood. The tusks grew by 2.5–15 cm (0.98–5.91 in) each year.[14]

Columbian mammoths had four functional molar teeth at a time, two in the upper jaw and two in the lower. About 23 cm (9.1 in) of the crown was within the jaw, and 2.5 cm (1 in) was above. The crown was continually pushed forwards and up as it wore down, comparable to a conveyor belt. The teeth had separated ridges of enamel, which were themselves covered in "prisms" that were directed towards the chewing surface. These were quite wear resistant and kept together by cementum and dentine. A mammoth had six sets of molars throughout a lifetime, which were replaced five times. The first molars were about the size of those of a human, 1.3 cm (0.51 in), the third were 15 cm (6 in) 15 cm (5.9 in) long, and the sixth were about 30 cm (1 ft) long and weighed 1.8 kg (4 lb). The molars grew larger and contained more ridges with each replacement.[14] The amount of plates also varied between individuals.[16] It took about 10.6 years to grow 180.9 mm of ridge.[17]

Palaeobiology[edit]

Outcrops on Goat Rock Beach possibly used as rubbing rocks by Columbian mammoths

As in modern elephants, the sensitive and muscular trunk worked as a limb-like organ with many functions. It was used for manipulating objects, and in social interactions. Adult mammoths could effectively defend themselves from predators with their tusks, trunks and size, but juveniles and weakened adults were vulnerable to pack hunters such as wolves and big cats. For example, bones of juvenile Columbian mammoths have been found in Friesenhahn Cave, Texas, accumulated by Homotherium (the scimitar-toothed-cat), but no animals could have hunted healthy adult mammoths. The tusks may have been used in intra-species fighting, such as territorial fights or fights over mates. Display of the large tusks of males could also have been used to attract females, and to intimidate rivals. Two Columbian mammoths from Nebraska that died with their tusks interlocked provide evidence of fighting behaviour. The mammoths could use their tusks as weapons by thrusting them, swiping them, or crashing them down. They also used the tusks in pushing contests by interlocking them, which sometimes resulted in breakage. Because of their curvature, the tusks were not suitable for stabbing. On Goat Rock Beach in the Sonoma Coast State Park of California, blueschist and chert outcrops now nicknamed "Mammoth Rocks" show evidence of having been rubbed by Columbian mammoths or mastodons. The rocks have polished areas 3-4 ms (10–13 ft) above the ground, mainly near their edges, and are similar to the rubbing rocks in present day Africa, used by elephants and other herbivores to rid themselves of mud and parasites. Similar sites are known from Hueco Tanks in Texas, and Cornudas Mountain in New Mexico.[18][19][20]

Restoration of a pair by a lake, Robert Bruce Horsfall, 1912

Accumulations of modern elephant remains have been termed "elephants' graveyards", as these sites were erroneously thought to be where old elephants went to die. Similar accumulations of mammoth bones have been found; it is thought these are the result of individuals dying near or in rivers over thousands of years, and their bones eventually being brought together by the streams (such as in the Acuilla River in Florida), or due to animals being mired in mud. Some accumulations are also thought to be the remains of herds that died together at the same time, perhaps due to flooding. Columbian mammoths are also rarely preserved in volcanic deposits, such as in Tocuila, Mexico, where volcanic lahar mud flow covered at least seven individuals 12,500 years ago. It is unknown how many mammoths that lived at one location at a time, but it is likely that the amount varied by season and life-cycle events. Modern elephants form large herds, sometimes consisting of multiple family groups, and these herds can include thousands of animals migrating together. Mammoths may have formed herds more often than modern elephants, as animals that live in open areas are more likely to do this than those in forested areas. It is unclear to what extent Columbian mammoths migrated, but an isotope study of Columbian mammoths from Blackwater Draw in New Mexico indicated that they had spent part of the year in the Rocky Mountains, 200 km (124 miles) away. Study of tusk rings may also help in further study of mammoth migration.[14][21][22]

Female "mammoth W" specimen at the Waco Mammoth Site

Like modern elephants, Columbian mammoths were likely very social and lived in matriarchal (female led) family groups. It is therefore probable that most of their other social behaviour was similar to that of modern elephants. This is supported by fossil assemblages, such as in the Dent Site in Colorado and the Waco Mammoth Site in Waco, Texas, where groups consisting entirely of female and juvenile Columbian mammoths have been found, implying female-led family groups. The latter assemblage includes 22 skeletons, with 15 individuals representing a herd of females and juveniles that died in a single event, probably a flash flood; the arrangement of some of the skeletons may imply that the females had formed a defensive ring around the juveniles. At the same site, another group consisting of a bull and six females also appears to have been killed by a flash flood; both incidents occurred between 64,000 and 73,000 years ago, but it is unknown whether the two groups died in the same event. At the Murray Springs Site in Arizona, where several Columbian mammoth skeletons have been excavated, a trackway similar to those of modern elephants leads up to one of the skeletons. This has been interpreted as having either been placed by the dead individual before it died, or as belonging to another individual that approached the dead or dying animal, similar to how modern elephants guard dead relatives for days.[14][21]

Natural traps[edit]

The male "Murray" specimen at the Hot Springs Mammoth Site

Many specimens also accumulated in natural traps such as sink holes and tar pits. The Hot Springs Mammoth Site in South Dakota (United States) represents a 26,000 year old and ca. 40 metre (130 ft) long sink hole that functioned for around 300 to 700 years, before it was filled with sediment. The site represents the opposite scenario of that in Waco; all but one of the at least 55 skeletons (additional skeletons are excavated each years) are male, accumulated over time rather than in a single event. It is assumed that like modern male elephants, male mammoths mainly lived alone and were more adventurous (especially the young adults), therefore more likely to end up in dangerous situations than the more cautious females. The mammoths may have been lured near the hole by warm water or vegetation near the edges, then slipped in and died of drowning or starvation. Isotope studies of growth rings have shown that most of the mammoths there had died during spring and summer, which may have correlated with the amount of vegetation near the sink hole. One individual, nicknamed "Murray", lies sprawled on its side, and probably ended in this pose while struggling to get free. Deep footprints that resulted from mammoths attempting to free themselves from the mud of the sink hole can be seen in vertically excavated sections of the site.[14][21]

Dire wolves mired in the La Brea tar pits, while fighting Smilodon over a Columbian mammoth carcass, Robert Bruce Horsfall, 1911

Excavations at the La Brea Tar Pits in Los Angeles, California, have since the early 20th century yielded 100 tonnes of fossils representing 600 species of flora and fauna, including several Columbian mammoths. The fossils from the tar pits are the remains of animals that became stuck in asphalt puddles that seeped to the surface of the pits, mainly between 40,000 and 11,500 years ago. Mired animals would die from hunger or exhaustion, and their corpses would attract predators, which were subsequently stuck themselves; the fossil record of the tar pits is dominated by predator remains, such as large canids and felids. Fossils of various different animals are found stuck together when excavated from the pits.[21] The tar pits do not preserve soft tissue, and a 2014 study concluded that asphalt may degrade DNA of animals deposited in it, after attempting to extract DNA from a Columbian mammoth from there.[23]

Diet[edit]

Underside of the skull of a male La Brea specimen nicknamed "Zed", showing upper molars

An adult Columbian mammoth would have needed more than 180 kg (400 lb) of food per day, and may have foraged as long as twenty hours per day. Mammoths chewed their food by using their powerful jaw muscles to move the mandible forwards while closing the mouth, then backwards while opening, which made the sharp enamel ridges cut across each other and grind the food. The ridges were wear-resistant to enable the animal to chew large quantities of food, which often contained grit. The trunk could be used for pulling up large tufts of grass, picking buds and flowers, or tearing leaves and branches from trees and shrubs. The tusks were also used to dig up plants and strip bark off trees. Digging is indicated on preserved tusks by flat, polished sections on the part of the surface that would have reached the ground.[14] Isotope studies of Columbian mammoths from Mexico and the United States have shown that that their diet varied by location and consisted of a mix of C3 (most plants) and C4 plants (such as grasses), which means they were not restricted to either grazing or browsing.[24]

Cast of the old male "Huntington mammoth", which had preserved stomach contents, Utah Museum of Natural History

Stomach contents from Columbian mammoths are rare, since no carcasses are known, but plant remains were found between the pelvis and ribs of the "Huntington mammoth" when it was excavated in Utah. Microscopic analysis showed that these chewed remains consisted of sedge, grass, fir twigs and needles, oak, and maple.[25] A large amount of mammoth dung has also been found in two caves in Utah. The dry conditions and stable temperature of the Bechan Cave ("Bechan" is Navajo for large faeces) has preserved 16,000 to 13,500 thousand year old elephant dung most likely belonging to Columbian mammoths. The dung consists of 95% grass and sedge, with 0-25% woody plants between boluses, including saltbush, sagebrush, water birch, and blue spruce. This is similar to the diet documented for the woolly mammoth, though browsing seems to have been more important for the Columbian mammoth in comparison. The cover of dung is 41 cm (16 in) thick, and has a volume of 227 m³ (8,000 cubic ft), with the largest boluses being 20 cm (8 in) in diameter. The Bechan dung could have been produced by a small group of mammoths over a relatively short time, since adult African elephants drop 11 kg (25 lb) of dung on average every second hour, and 90–135 kg (200-300 lb) each day.[14][26]

It has been proposed that giant North American fruits of plants such as the Osage-orange, Kentucky coffee and Honey locust evolved in tandem with now extinct American megafauna, such as mammoths and other proboscideans, as there are no extant endemic herbivores able to ingest these fruits and disperse their seeds. Introduced cattle and horses have since taken over this ecological role.[27][28]

Life history[edit]

Skeleton of a juvenile, Natural History Museum of Utah

Columbian mammoths are thought to have lived roughly 80 years. The lifespans of mammals are related to their size; Columbian mammoths are larger than modern elephants, which have a lifespan of approximately 60 years. The age of a mammoth can be roughly determined by counting the growth rings of its tusks when viewed in cross section. Such ring counting does not account for mammoths' early years, however; a mammoths' early growth is represented in the tips of the tusks, which are usually worn away. In the remainder of the tusk, each major line represents a year, and weekly and daily lines can be found in between. Dark bands correspond to summers, and it is therefore possible to determine the season in which a mammoth died. The growth of the tusks slowed when it became harder to forage, as when a mammoth was diseased or a male mammoth was banished from the herd.[14]

Mammoths continued growing during adulthood, as do other elephants. Males grew until age 40, and females grew until age 25. Mammoths may have had gestation periods of 21–22 months, like those of modern elephants. Columbian mammoths had six sets of molars that emerged over the course of their lifespans. At the age of 6–12 months, the second set of molars would be in the process of erupting, and the first set would be worn out at 18 months of age. The third set of molars lasted for ten years, and this process was repeated until the final, sixth set emerged when the animal was 30 years old. When the last set of molars was worn out, the animal would be unable to chew and feed, and it would die of starvation.[14]

Almost all vertebrae of the "Huntington mammoth", a very old specimen, were deformed by arthritic disease, and four of its lumbar vertebrae were fused. Some bones also have evidence of bacterial infections, such as osteomyelitis.[14] The condition of the bones suggests the specimen died of old age and malnutrition.[25]

Distribution and habitat[edit]

Environment around the La Brea Tar Pits, with Columbian mammoth herd in the background, Charles R. Knight, 1921

Columbian mammoths inhabited the southern half of North America, ranging from the northern United States, across Mexico, and as far south as Costa Rica. The single Costa Rican specimen, a molar, was reported in 1963, but has since been lost.[29] The environment in these places may have had more varied habitats than those areas inhabited by woolly mammoths in the north (the mammoth steppe). Some areas were covered by grass, herbaceous plants, trees and shrub; the exact composition varied from region to region, including grassland, savannah-like, and parkland habitats. There were also various woodlands, and though mammoths would not have preferred forests, clearings within them could provide them with grass and herbs.[14]

Possible distribution of the Columbian mammoth (red) and the woolly mammoth (blue) in North America, based on locations of fossil finds

The Columbian mammoth shared its habitat with other now-extinct Pleistocene mammals such as Glyptodon, Smilodon (the sabre-toothed cat), ground sloths, Camelops, the American mastodon, as well as horses and buffalos. It did not live in the Arctic regions of Canada, which were instead inhabited by woolly mammoths. Fossils of woolly mammoths and Columbian mammoths have been found in the same localities in a few areas of North America where their regions overlapped, including the Hot Springs Site. It is unknown whether the two species were sympatric and lived there simultaneously, or if the woolly mammoths had entered these southern areas during times when Columbian mammoth populations were absent there.[6] The Columbian mammoth also co-occurred alongside the other extinct proboscideans Stegomastodon mirificus and Cuvieronius tropicus at sites in Texas and New Mexico, during the early Irvingtonian.[30]

Relationship with humans[edit]

Fanciful restoration of a Columbian mammoth hunt, J. Steeple Davis, 1885

Humans entered the Americas through Beringia, and various evidence documents their interactions with Columbian mammoths. Tools made from modified Columbian mammoth remains have been discovered in several sites in North America. At Tocuila (Texcoco) in Mexico, mammoth bones were quarried 13,000 years ago to produce lithic flakes and lithic cores. At the Lange-Ferguson Site in South Dakota, the remains of two mammoths were found alongside two 12,800-year-old cleaver choppers made from a mammoth shoulder blade; the choppers had been used to butcher the mammoth carcasses. At the same site, a flake knife made from a long mammoth bone was also found wedged against some mammoth vertebrae. At Murray Springs, archaeologists discovered a 13,100-year-old object made from a mammoth femur; the object is thought to be shaft wrench, a tool for straightening wood and bone.[31][32]

Evidence of the earliest mammoth butchering dates to 21,500 to 22,000 years ago. However, Palaeoamericans of the Clovis culture (which arose 7000 years later) may have been the first humans to hunt mammoths extensively. These people are thought to have hunted Columbian mammoths using spears pointed with Clovis points. These spears may have been thrown or thrusted. Clovis points have been found in association with Columbian mammoth remains at several sites, though archaeologists do not agree about whether all these finds represent the hunting or scavenging of dead mammoths, or simply the accidental association of Clovis points and mammoth bones. A female mammoth at the Naco-Mammoth Kill Site in Arizona was found with eight Clovis points near its skull, shoulder blade, ribs and other bones; it is considered the most convincing evidence for hunting. Replica spears in modern experiments have been able to penetrate the ribcages of African elephants; in these experiments, reuse resulted in little damage to the points.[33][34]

Other sites show more circumstantial evidence of mammoth hunting, such as piled bones bearing butcher marks. Some of these sites are not closely associated with Clovis points. The Lehner Mammoth-Kill Site and the Dent Site, where multiple juvenile and adult mammoths have been found with butcher marks and in association with Clovis points, were once interpreted as the killing of entire herds by Clovis hunters. However, isotope studies have shown that the accumulations represent individual deaths at different seasons of the year, and therefore not herds killed in single incidents. Many other such assemblages of bones with butcher marks may also represent accumulations over time, and are therefore ambiguous as evidence for large scale hunting.[33][35]

Tracing of petroglyphs from Utah depicting two Columbian mammoths; a bison carving is superimposed upon one of the mammoth carvings

Petroglyphs in the Colorado Plateau depict either Columbian mammoths or mastodons.[31] A 13,000-year-old bone fragment from Vero Beach, Florida, the earliest example of art in the Americas, is engraved with either a mammoth or a mastodon.[36] 11,000-13,000-year-old petroglyphs from the San Juan River in Utah are thought to include depictions of two Columbian mammoths; the mammoths' domed heads distinguish them from mastodons. They are also shown with two "fingers" on their trunks, a feature known from European depictions of mammoths. The tusks are short, which may indicate they are meant to be females. A carving of a bison (possibly the extinct Bison antiquus) is superimposed on one of the mammoth carvings and may be a later addition. Other possible depictions of Columbian mammoths have been shown to be either misinterpretations or fraudulent.[37]

The Columbian mammoth is the state fossil of Washington.[38] Nebraska's state fossil is "Archie", a Columbian mammoth specimen found in the state in 1922. "Archie" is currently on display at Elephant Hall in Lincoln, Nebraska, and is the largest mounted mammoth specimen in the United States.[39]

Extinction[edit]

Clovis points from the Rummells-Maske Cache Site, Iowa

Columbian and woolly mammoths both disappeared during the late Pleistocene and early Holocene, alongside most of the Pleistocene megafauna.[33] The most recent Columbian mammoth remains have been dated to around 11,000 years ago.[40][41][42] This extinction formed part of the Quaternary extinction event, which began 40,000 years ago and peaked between 14,000 and 11,500 years ago.[33] Scientists do not know whether these extinctions happened abruptly or were drawn out.[40][43] During this period, 40 mammal species disappeared from North America, almost all of which weighed over 40 kg (90 lb); the extinction of the mammoths cannot be explained in isolation.[33]

Scientists are divided over whether climate change or hunting (or a combination of the two) drove the extinction of the Columbian mammoths. According to the climate change hypothesis, warmer weather led to the shrinking of suitable habitat for Columbian mammoths, which turned from parkland to forest, grassland and semi-desert, with less diverse vegetation. The overkill hypothesis, on the other hand, attributes the extinction to hunting by humans.[33] This idea was first proposed by Paul S. Martin in 1967;[44] more recent research on this subject is mixed. A 2002 study concluded that the archaeological record did not support the overkill hypothesis, given that only 14 Clovis sites (12 with mammoth remains and two with mastodon remains) out of 76 examined provided strong evidence of hunting.[45] In contrast, a 2007 study found that the Clovis record indicated the highest frequency of prehistoric exploitation of proboscideans for subsistence in the world, and supported the overkill hypothesis.[46] Whatever the actual cause of extinction, large mammals are generally more vulnerable than smaller ones due to their smaller population size and low reproduction rates.[33]

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Bibliography[edit]

  • Lister, A.; Bahn, P. (2007). Mammoths - Giants of the Ice Age (3 ed.). London: Frances Lincoln. ISBN 978-0-520-26160-0. 

External links[edit]