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, the common name for the extinct elephant genus Mammuthus. The Columbian mammoth was one of the last in a line of mammoth species, beginning with Mammuthus subplanifrons in the early Pliocene. M. columbi diverged from the steppe mammoth, M. trogontherii, which had entered North America about 1.5 million years ago. Its closest extant relative is the Asian elephant.

It lived in the Quaternary period and appeared in North America (in the present United States and to as far south as Nicaragua and Honduras) during the late Pleistocene. It had long, curved tusks and four molars, which were replaced six times during the lifetime of an individual. Its behaviour was similar to that of modern elephants, and it used its tusks and trunk for manipulating objects, fighting, and foraging.

The Columbian mammoth reached 4 m (13 ft) at the shoulders, and it weighed up to about 10 tonnes.

Taxonomy[edit]

Partial holotype molar, 1863

The Columbian mammoth was first scientifically described by Scottish naturalist Hugh Falconer in 1857, based on a partial upper molar found during the excavation of the Brunswick Altamaha Canal in Georgia in the south eastern United States.[1] The etymology of the word mammoth itself is unclear, but it was first used in Europe during the early 17th century, when referring to maimanto tusks discovered in Siberia.[2]

American mammoths were classified in many different genera until the start of the 20th century.[3] Other species of North American mammoths, such as the imperial mammoth (Mammuthus imperator) and Jefferson's mammoth (Mammuthus jeffersoni, after Thomas Jefferson) were described as more primitive and advanced stages of evolution than the Columbian mammoth, but these are not thought to be distinct species today.[4] Palaeontologist Larry Agenbroad believes that M. imperator is a non-valid name given to unusually large M. columbi. Given that proboscidean tusks grow throughout the animal's life, older animals will tend to have longer tusks, which are more likely to cross. He has also mooted the alternative interpretation that M. imperator represents a subspecies of large M. columbi.[5] This has also been accepted by other scientists.[6]

Evolution[edit]

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

The earliest known proboscideans, 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 and the hyraxes. 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 is only a distant relative of the mammoths, and part of the distinct family Mammutidae, which diverged 25 million years before the mammoths evolved.[4] The following cladogram shows the placement of the Columbian mammoth among other proboscideans, based on hyoid characteristics:[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 plates) on their molars; primitive species had few ridges, and the number increased gradually as new species evolved and replaced the preceding ones. The crowns of the teeth lengthened and the skulls became taller to accommodate this. At the same time, the skulls became shorter from front to back to minimise the weight.[8] The short and tall skulls of woolly and Columbian mammoths are the culmination of this process.[4] These adaptations were acquired gradually as mammoths turned to more abrasive food items.[9]

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 type known from there has been named M. rumanus, which 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 c. 2-1.5 million years ago.[8] The Columbian mammoth, M. columbi, 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, and 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.[4]

Cast of the "Huntington mammoth", morphologically a Columbian mammoth, but genetically nested among woolly mammoths, Utah Museum of Natural History

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. The authors of the study also suggested that the North American form known as M. jeffersonii may have been a hybrid between the two species.[10] A 2014 study concluded that asphalt may degrade DNA of animals deposited in it, after attempting to extract DNA from a Columbian mammoth from the La Brea tar Pits.[11]

A population of Columbian mammoths that lived between 50.000 and 13.000 years ago on the Channel Islands of California, 10 km (6 miles) away from the mainland, evolved very small size. They were 1.2-1.8 m (4-6 ft) tall at the shoulders and weighed 1 ton, which is less than half the size of the mainland Columbian mammoths, and they are therefore considered the distinct species M. exilis, the "pygmy mammoth". These mammoths presumably reached the islands by swimming there, and decreased in size due to scarcity of food on the small areas. Bones of larger mammoths have also been found on the islands, but it is unknown whether these were stages in the dwarfing process, or later arrivals to the islands.[4]

Description[edit]

Restoration by Charles R. Knight, 1909

The shoulder height of the Columbian mammoth reached 4 m (13 ft), and it weighed up to about 10 tonnes, which is equal to the weight of 130 adult humans. This is larger than modern African elephants and the woolly mammoth, which reach about 2.7 to 3.4 m (9–11 ft). Female mammoths were smaller and more lighter built than males. Soft tissue of Columbian and other mammoths is not known, so much less is known about their 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. The tail of the Columbian mammoth was intermediate in length between that of modern elephants and the woolly mammoth.[12]

Size (blue) compared to other proboscideans

Hair believed 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.[12] The fur was probably less dense than that of woolly mammoths, due to the warmer habitat.[4]

Dentition[edit]

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

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.[12]

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.[12] The amount of ridges exceeded 20, and varied across individuals.[13] It took about 10.6 years to grow 180.9 mm of ridge.[14]

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 large felines. Bones of juvenile Columbian mammoths were accumulated by Homotherium, the scimitar-toothed-cat, in Friesenhahn Cave, Texas, but no animals could have hunted healthy adult mammoths. The tusks may also 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. Because of their curvature, the tusks were not suitable for stabbing, but may have been used for hitting. Two Columbian mammoths that died with their tusks interlocked found in Nebraska provide evidence of fighting behaviour. The mammoths used 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. On Goat Rock Beach in the Sonoma Coast State Park of Californoa, 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.[15]

Female specimen ("mammoth W") at the Waco Mammoth Site

It is unknown how many mammoths lived at one location at a time, as fossil deposits are often accumulations of individuals that died over long periods of time. It is likely that the amounts varied by season and life-cycle events. Modern elephants form large herds, sometimes formed by multiple family groups, sometimes including thousands of animals migrating together. Mammoths may have formed herds more often, as animals that live in open areas are more likely to form herds 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. 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 the rivers over thousands of years, and their bones eventually being brought together by the streams, 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.[12] Many specimens also accumulated in "natural traps" such as sink holes ans kettle holes and tar pits.[2]

Excavation at the Mammoth Site, Hot Springs, once a sinkhole that trapped several males

Like modern elephants, Columbian mammoths were likely very social and lived in matriarchal family groups. It is therefore probable that most of their other social behaviour was similar to those 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, and the arrangement of some of the skeletons may imply that 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 64.000-73.000 years ago, but it is unknown whether the two groups died in the same event. At Murray Springs 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.[2][12]

Natural traps[edit]

A different scenario is found at the Hot Springs Mammoth Site in South Dakota, where 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. The site represents a 26,000 year old and ca. 40 metre long (130 ft) sinkhole that operated for around 300 to 700 years, before it was filled with sediment. 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 lured near the hole by warm waters or vegetation near the edges.[2][12]

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

The remains of Columbian mammoths were discovered in the La Brea Tar Pits, located in Los Angeles, California, and the skeleton of one of them is on exhibit in that site's museum. The Waco Mammoth Site in Waco, Texas, has, so far, produced a collection of bones from 19 females and juveniles who are believed to have died in the same flood event, as well as the skeletons of other mammoths who died in separate flood events.[16]

Diet[edit]

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

An adult Columbian mammoth would have needed more than 180 kg (400 lb) of food, and may have foraged as long as twenty hours every day. Mammoths chewed their food by using their powerful jaw muscles to move the mandible forwards and close 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 off large grass tufts, picking buds and flowers, and tearing off leaves and branches where trees and shrubs were present. The tusks were also used for obtaining food, such as digging up plants and stripping off bark. This is indicated on many preserved tusks by flat, polished sections up to 30 centimetres (12 in) long on the part of the surface that would have reached the ground.[12]

Mandible with lower molars, Palaeontological Museum in Tocuila, Mexico

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. These masticated remains were shown to consist of sedge, grass, fir twigs and needles, oak, and maple, through microscopic analysis. A large amount of Columbian 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 16.000-13.500 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 wolly 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.[12]

It is also theorized that the Columbian Mammoth ate the giant fruits of North America, such as the Osage-orange, Kentucky coffee and Honey locust, as there was no other large herbivore in North America at that time that could ingest these fruits.

Life history[edit]

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

Since modern elephants have gestation periods of 21–22 months, this was possibly true for mammoths as well. The lifespan of mammals is related to their size, and since modern elephants can reach the age of 60 years, the same is thought to be true for woolly mammoths which were of a similar size. Since Columbian mammoths were even larger, they may have lived up to 80 years. The age of a mammoth can be roughly determined by counting the growth rings of its tusks when viewed in cross section, but this does not account for their early years, as these are represented by the tips of the tusks, which are usually worn away. In the remaining part of the tusk, each major line represents a year, and weekly and daily ones 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, for example during disease, or when a male was banished from the herd. Mammoths continued growing past adulthood, like other elephants. Unfused limb bones show that males grew until they reached the age of 40, and females grew until they were 25. 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.[12]

Skeleton of a juvenile, Natural History Museum of Utah

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.[12]

Distribution and habitat[edit]

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

The Columbian mammoth inhabited the southern half of North America, which may have had more varied habitats than those areas inhabited by woolly mammoths. Some areas were covered by grass, herbaceous plants, trees and shrub; the exact composition varied from region to region, including grassland, savanna-like, and parkland habitats. There were also various woodlands, and though mammoths would not have preferred forests, clearings within them could provide grass and herbs.[12] The Columbian mammoth shared its habitat with other now-extinct Pleistocene mammals such as Glyptodon, the saber-toothede-cat (Smilodon), ground sloths, Camelops, the distantly related American mastodon (Mammut americanum), as well as horses and buffalos.[4]

Columbian mammoths inhabited North America from the United States, across Mexico, and as far south as Costa Rica. 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 together in a few localities of North America, including the Hot Springs sinkhole of South Dakota where their regions overlapped. It is unknown whether the two species were sympatric and lived there simultaneously, or if the woolly mammoths may have entered these southern areas during times when Columbian mammoth populations were absent there.[4]

In 1998, the Washington State Legislature approved the Columbian mammoth as the state fossil.[17] Additionally, a specimen found in Nebraska in 1922 and named "Archie" is the state's official fossil. "Archie" is currently on display at Elephant Hall in Lincoln, Nebraska, and is the largest mounted mammoth specimen in the United States.[18]

This mammoth also lived in Mexico, where its remains are very common. A large individual is the central exhibit in the Regional Museum of Guadalajara, in the Mexican state of Jalisco.[19]

The most recent excavation of a Columbian mammoth's remains, which were at a site south of Mexico City, was in March 2013. As these remains had been blanketed in thick volcanic ash about 1 meter (3.3 feet) thick, ground-penetrating radar) was used to locate the fossil. According to local researchers, the mammoth died circa 10,000 BCE–8,000 BCE, at the age of approximately 30 and was the most complete skeleton ever to be found in the country (approximately 70% total by mid-April). As early as 2012, residents of the nearby town of Santa Ana Tlacotenco uncovered the animal's teeth, which were partially concealed by cacti.[20]

Relationship with humans[edit]

Petroglyphs depicting two Columbian mammoths, with a bison superimposed

In 2011, two 11,000-13,000 year old petroglyphs thought to depict Columbian mammoths were reported at the San Juan River in Utah.[21] Petroglyphs in the Colorado plateau may depict Columbian mammoths, if they are not mastodons instead.[22]

Extinction[edit]

The Columbian mammoth was one of the last members of the American megafauna to go extinct, with the date of disappearance generally set at approximately 12,500 years ago.[23] However, several specimens have been dated to 9,000 years ago or less, and one near Nashville, Tennessee was dated to only about 7,800 years ago. However, dates younger than 11,000 BP have not been viewed as credible.[24]

References[edit]

  1. ^ Patterson, D. B.; Mead, A. J.; Bahn, R. A. (2012). "New skeletal remains of Mammuthus columbi from Glynn County, Georgia with notes on their historical and paleoecological significance". Southeastern Naturalist 11 (2): 163–172. doi:10.1656/058.011.0201.  edit
  2. ^ a b c d Lister, 2007. pp. 45–75
  3. ^ Osborn, H. F. (1942). Percy, M. R., ed. Proboscidea: A monograph of the discovery, evolution, migration and extinction of the mastodonts and elephants of the world 2. New York: J. Pierpont Morgan Fund. pp. 935–1115. 
  4. ^ a b c d e f g h Lister, 2007. pp. 12–43
  5. ^ Agenbroad, L. D. (2005). "North American Proboscideans: Mammoths: The state of Knowledge, 2003". Quaternary International. 126-128: 73–25. Bibcode:2005QuInt.126...73A. doi:10.1016/j.quaint.2004.04.016.  edit
  6. ^ McDaniel, G. E.; Jefferson, G. T. (2006). "Mammoths in our midst: The proboscideans of Anza-Borrego Desert State Park®, Southern California, USA". Quaternary International. 142-143: 124. Bibcode:2006QuInt.142..124M. doi:10.1016/j.quaint.2005.03.011.  edit
  7. ^ Shoshani, J.; Tassy, P. (2005). "Advances in proboscidean taxonomy & classification, anatomy & physiology, and ecology & behavior". Quaternary International. 126–128: 5. Bibcode:2005QuInt.126....5S. doi:10.1016/j.quaint.2004.04.011.  edit
  8. ^ a b Lister, A. M.; Sher, A. V.; Van Essen, H.; Wei, G. (2005). "The pattern and process of mammoth evolution in Eurasia". Quaternary International. 126–128: 49. Bibcode:2005QuInt.126...49L. doi:10.1016/j.quaint.2004.04.014.  edit
  9. ^ Ferretti, M. P. (2003). "Structure and evolution of mammoth molar enamel". Acta Palaeontologica Polonica. 3 48: 383–396. 
  10. ^ Enk, J.; Devault, A.; Debruyne, R.; King, C. E.; Treangen, T.; O'Rourke, D.; Salzberg, S. L.; Fisher, D.; MacPhee, R.; Poinar, H. (2011). "Complete Columbian mammoth mitogenome suggests interbreeding with woolly mammoths". Genome Biology 12 (5): R51. doi:10.1186/gb-2011-12-5-r51. PMC 3219973. PMID 21627792.  edit
  11. ^ Gold, D. A.; Robinson, J.; Farrell, A. B.; Harris, J. M.; Thalmann, O.; Jacobs, D. K. (2014). "Attempted DNA extraction from a Rancho La Brea Columbian mammoth (Mammuthus columbi): Prospects for ancient DNA from asphalt deposits". Ecology and Evolution 4 (4): 329–336. doi:10.1002/ece3.928.  edit
  12. ^ a b c d e f g h i j k l Lister, 2007. pp. 77–95
  13. ^ McDaniel, G. E.; Jefferson, G. T. (2006). "Dental variation in the molars of Mammuthus columbi var. M. Imperator (Proboscidea, Elephantidae) from a Mathis gravel quarry, southern Texas". Quaternary International. 142-143: 166–177. doi:10.1016/j.quaint.2005.03.014.  edit
  14. ^ Dirks, W.; Bromage, T. G.; Agenbroad, L. D. (2012). "The duration and rate of molar plate formation in Palaeoloxodon cypriotes and Mammuthus columbi from dental histology". Quaternary International 255: 79–85. doi:10.1016/j.quaint.2011.11.002.  edit
  15. ^ Lister, 2007. pp. 96–111
  16. ^ "Waco Mammoth Site - Waco, Texas". Retrieved 16 October 2013. 
  17. ^ "Washington State Fossil". State Symbols USA. Retrieved 16 October 2013. 
  18. ^ "Nebraska State Fossil". State Symbols USA. Retrieved 16 October 2013. 
  19. ^ Boyd, Mildred. "The Regional Museum of Guadalajara". Retrieved 4 December 2012. 
  20. ^ "Mammoth remains discovered in Mexico". Light Years. Cable News Network. April 16, 2013. Retrieved 16 October 2013. 
  21. ^ Malotki, Ekkehart and Wallace, Henry D. Columbian mammoth petroglyphs from the San Juan River near Bluff, Utah, United States [online]. Rock Art Research: The Journal of the Australian Rock Art Research Association (AURA), Vol. 28, No. 2, Nov 2011
  22. ^ Lister, 2007. pp. 113–139
  23. ^ BBC - Science & Nature - Wildfacts - Columbian mammoth
  24. ^ Fiedel, S. (2009). "Sudden Deaths: The Chronology of Terminal Pleistocene Megafaunal Extinction". American Megafaunal Extinctions at the End of the Pleistocene. Vertebrate Paleobiology and Paleoanthropology. pp. 21–37. doi:10.1007/978-1-4020-8793-6_2. ISBN 978-1-4020-8792-9.  edit

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]