Columbian mammoth

An adult Columbian mammoth would have needed more than 180 kg (400 lb) of food per day, and may have foraged for 20 hours a day. Mammoths chewed their food using their powerful jaw muscles to move the mandible forward and close the mouth, then backward while opening; the sharp enamel ridges thereby cut across each other, grinding the food. The ridges were wear-resistant, enabling the animal to chew large quantities of food that 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, and the tusks were used to dig up plants and strip bark from trees. Digging is indicated on preserved tusks by flat, polished sections of the surface that would have reached the ground.^[21] Isotope studies of Columbian mammoths from Mexico and the United States have shown that their diet varied by location, consisting of a mix of C3 (most plants) and C4 plants (such as grasses), and they were not restricted to grazing or browsing.^[37][38][39] Even individual Columbian mammoths from the same geographic location show major differences in dental mesowear, indicating extensive variation in dietary habits between different individuals within the same population.^[40]

Stomach contents from Columbian mammoths are rare, since no carcasses have been found, but plant remains were discovered between the pelvis and ribs of the "Huntington mammoth" when it was excavated in Utah. Microscopy showed that these chewed remains consisted of sedges, grasses, fir twigs and needles, oak, and maple.^[41] A large amount of mammoth dung has been found in two caves in Utah. The dry conditions and stable temperature of Bechan Cave (bechan is Navajo for "large faeces") has preserved 16,000- to 13,500-year-old elephant dung, most likely from Columbian mammoths.^[42] The dung consists of 95% grasses and sedges, and varies from 0 to 25% woody plants between dung boluses, including saltbush, sagebrush, water birch, and blue spruce. This is similar to the diet documented for the woolly mammoth, although browsing seems to have been more important for the Columbian mammoth. 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 20 cm (7.9 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 an average of 11 kg (24 lb) of dung every two hours and 90–135 kg (198–298 lb) each day.^[21][43]

Giant North American fruits of plants such as the Osage-orange, Kentucky coffeetree, pawpaw and honey locust have been proposed to have evolved in tandem with now-extinct American megafauna such as mammoths and other proboscideans, since no extant endemic herbivores are able to ingest these fruits and disperse their seeds. Introduced cattle and horses have since taken over this ecological role.^[44][45][46]

Life history

Skeleton of a juvenile (left) and cast of the male "Huntington mammoth" (right), which was old and sick when it died, both at the Natural History Museum of Utah

The lifespan of the Columbian mammoth is thought to have been about 80 years. The lifespan of a mammal is related to its size; Columbian mammoths are larger than modern elephants, which have a lifespan of about 60 years. The age of a mammoth can be roughly determined by counting the growth rings of its tusks when viewed in cross section. However, ring-counting does not account for a mammoth's early years; early growth is represented in tusk tips, which are usually worn away. In the remainder of the tusk, each major line represents a year, with weekly and daily lines found in between. Dark bands correspond to summer, making determining the season in which a mammoth died possible. Tusk growth slowed when foraging became more difficult, such as during illness or when a male mammoth was banished from the herd (male elephants live with their herds until about the age of 10).^[21]

Mammoths continued growing during adulthood, as do other elephants. Males grew until age 40, and females 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 in the course of a lifetime. At 6–12 months, the second set of molars would erupt, with the first set worn out at 18 months of age. The third set of molars lasted for 10 years, and this process was repeated until the sixth set emerged at 30 years of age. When the last set of molars wore out, the animal would be unable to chew, and would die of starvation.^[21]

Almost all vertebrae of the "Huntington mammoth", a very aged specimen, were deformed by arthritic disease, and four of its lumbar vertebrae were fused; some bones also indicate bacterial infection, such as osteomyelitis.^[21] The condition of the bones suggests the specimen died of old age and malnutrition.^[41]

Distribution and habitat

Columbian mammoths inhabited the much of North America, ranging from southern Canada^[47] to Central America (where it was largely confined to the vicinity of the Pacific coast), with its southernmost record being in northern Costa Rica.^[48] The environment in these areas may have had more varied habitats than those inhabited by woolly mammoths in the north (the mammoth steppe). Some areas were covered by grasses, herbaceous plants, trees, and shrubs; their composition varied from region to region, and included grassland, savanna, and aspen parkland habitats. Wooded areas also occurred; although mammoths would not have preferred forests, clearings in them could provide the animals with grasses and herbs.^[21]

The Columbian mammoth shared its habitat with other now-extinct Pleistocene mammals such as

Relationship with humans

Towards the end of the Late Pleistocene, around or after 16,000 years ago,

cleaver choppers made from a mammoth shoulder blade; the choppers had been used to butcher the mammoths. At the same site, a flake knife made from a long mammoth bone was also found wedged against mammoth vertebrae. At Murray Springs, archeologists discovered a 13,100-year-old object made from a mammoth femur; the object is thought to be a shaft wrench, a tool for straightening wood and bone to make spear-shafts (the Inuit use similar tools).^[52][53]

Although some sites potentially documenting human interactions with Columbian mammoths have been reported from as early 20,000 years ago, these have been criticised, as they lack stone tools, and the supposed human-made marks on the bones are potentially the result of natural processes.

Naco-Mammoth Kill Site in Arizona, found with eight Clovis points near its skull, shoulder blade, ribs, and other bones, is considered the most convincing evidence for hunting. In modern experiments, replica spears have been able to penetrate the rib cages of African elephants with reuse causing little damage to the points.^[55][56]

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 Dent site (the first evidence of mammoth hunting in North America, discovered in 1932) and the Lehner Mammoth-Kill 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, so are not herds killed in single incidents. Many other such assemblages of bones with butcher marks may also represent accumulations over time, so are ambiguous as evidence for large-scale hunting.^[55][57]

A 2021 article by the American paleontologist Metin I. Eren and colleagues suggested mammoths were not very susceptible to Clovis point weapons due to their thick skin, hair, muscles, ribs, and fat, which would have impeded most types of attacks humans could pull off at that time. Experiments wherein most spear points used to calculate their effectiveness against simulated mammoth skin shattered on impact rather than penetrating, suggested to these researchers that ancient humans probably preferred to scavenge mammoth carcasses for their meat and other resources and threw spears to drive other scavengers away from carcasses before butchering the corpse with their stone tools. While the study does not rule out the hunting of mammoths by early humans, it instead indicates that such an event was probably rare and potentially more dangerous and less rewarding than scavenging. In response, other scientists found no reason to abandon the traditional idea that Clovis points were used to hunt big-game, one suggesting that such spears could have been thrown or thrust at areas of the torso that were not protected by ribs, with the wounds not killing the mammoths instantly, but the hunters could follow their prey until it had bled to death.^[58][59]

petroglyphs from Utah supposedly depicting mammoths and a bison

(right), though it may have been made after mammoths went extinct

San Juan River in Utah have been suggested to be 11,000–13,000-years old and 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.^[62] Geological dating of the San Juan River depictions in 2013 have shown them to be less than 4000 years old, after mammoths and mastodons went extinct, and they may instead be an arrangement of unrelated elements.^[61][63] Other possible depictions of Columbian mammoths have been shown to be either misinterpretations or fraudulent.^[62]

The Columbian mammoth is the state fossil of Washington^[64] and South Carolina.^[65] 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.^[66]

Extinction

Clovis points at the Dent site, the first evidence of mammoth hunting in America, Carnegie Museum of Natural History (left), and 13,500–13,000 year old Clovis points at Cleveland Museum of Natural History

(right)

Columbian and woolly mammoths both disappeared from mainland North America by the latest Pleistocene, with no recorded Holocene survival, alongside most other latest Pleistocene megafauna of North America. The latest calibrated radiocarbon date of the Columbian mammoth is in the locality of the Dent site in Colorado which dates to 12,124–12,705 years Before Present, during the onset of the Younger Dryas cold phase (12,900-11,700 years BP) and Clovis culture (13,200-12,800 years BP). Its younger calibrated date compared to most other extinct latest Pleistocene species suggests that it was one of the last North American megafauna to have gone extinct.^[67] Amongst the most recent Columbian mammoth remains have been dated around 10,900 years ago, although the date is uncalibrated and therefore is actually older in age.^[68][69][70] This extinction formed part of the Late Pleistocene extinctions of North America, which coincided with both Clovis culture and the Younger Dryas.^[55] Scientists do not know whether these extinctions happened abruptly or were drawn out.^[68][71] During this period, 40 mammal species disappeared from North America, almost all of which weighed over 40 kg (88 lb); the extinction of the mammoths cannot be explained in isolation.^[55]

Scientists are divided over whether climate change, 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 semidesert, with less diverse vegetation. The "overkill hypothesis" attributes the extinction to hunting by humans, an idea first proposed by geoscientist Paul S. Martin in 1967; more recent research on this subject has varied in conclusions.^[55][72]

A 2002 study concluded that the archeological 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.^[73] 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".^[74] A 2019 study that used mathematical modelling to simulate correlations between migrations of humans and Columbian mammoths also supported the "overkill hypothesis".^[75] Whatever the actual cause of extinction, large mammals are generally more susceptible to hunting pressure than smaller ones due to their smaller population size and low reproduction rates.^[55] On the other hand, large mammals are generally less vulnerable to climatic stresses since they have greater fat deposits at their disposal^[76] and can migrate long distances to escape food shortages.^[77]

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Bibliography

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External links

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• Media related to Mammuthus columbi at Wikimedia Commons
• Data related to Mammuthus columbi at Wikispecies
• Mammoth Mystery –
  Nova
  documentary about the fighting mammoths of Nebraska
• Footage showing removal of a Columbian mammoth skull at the Hot Springs Mammoth Site

1. ^ Lister & Bahn 2007.

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