Columbian mammoth
The Columbian mammoth is an extinct species of mammoth that inhabited North America from southern Canada to Costa Rica during the Pleistocene epoch. The Columbian mammoth descended from Eurasian steppe mammoths that colonized North America during the Early Pleistocene around 1.5–1.3 million years ago, and later experienced hybridisation with the woolly mammoth lineage. The Columbian mammoth was among the last mammoth species, and the pygmy mammoths evolved from them on the Channel Islands of California. The closest extant relative of the Columbian and other mammoths is the Asian elephant.
Reaching at the shoulders and in weight, the Columbian mammoth was one of the largest species of mammoth, larger than the woolly mammoth and the African bush elephant. It had long, curved tusks and four molars at a time, 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 sedges, grasses, 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 because they died in incidents such as a drought, or because these locations were natural traps in which individuals accumulated over time.
For a few thousand years prior to their extinction, Columbian mammoths coexisted in North America with Paleoindians – the first humans to inhabit the Americas – who hunted them for food, used their bones for making tools, and possibly depicted them in ancient art. Columbian mammoth remains have been found in association with Clovis culture artifacts. The Clovis peoples are suggested to have been specialized mammoth hunters, though they possibly also scavenged their remains. The last Columbian mammoths are dated to about ~12,000 years ago, with the species becoming extinct as part of the Late Pleistocene extinction event, simultaneously with most other large megafaunal mammals present in the Americas. It is one of the last recorded North American megafauna to have gone extinct. The extinction of the Columbian mammoth and other American megafauna was most likely a result of habitat loss caused by climate change, hunting by humans, or a combination of both.
Taxonomy
Around 1725, enslaved Africans digging in the vicinity of the Stono River in South Carolina unearthed 3-4 molar teeth now known to have belonged to Columbian mammoths, which were subsequently examined by the British naturalist Mark Catesby, who visited the site, and published his account of the visit in 1743. While the slave owners were puzzled by the objects and suggested that they originated from the great flood described in the Bible, Catesby noted that the slaves unanimously agreed that the objects were in fact the teeth of elephants, similar to those of African elephants that they were familiar with from their homeland, to which Catesby concurred, marking the first technical identification of any fossil animal in North America. A similar observation was made in 1782 after enslaved Africans had excavated mammoth bones and teeth from a salt marsh in Virginia. These remains were subsequently sent on by US army commander Arthur Campbell to future US president Thomas Jefferson. Campbell noted in a letter that several Africans had seen one of the teeth, and "All... pronounced it an elephant." Catesby's account was later noted by the French paleontologist Georges Cuvier around the beginning of the 19th century, with Cuvier personally examining the teeth from Stono, which he used to support his theory of catastrophism.File:Mammuthus columbi molar.jpg|thumb|left|alt=Large mammoth tooth|1863 lithograph of the partial holotype molar from Georgia
The Columbian mammoth was first scientifically described in 1857 by the Scottish naturalist Hugh Falconer, who named the species Elephas columbi after the explorer Christopher Columbus. The animal was brought to Falconer's attention in 1846 by the Scottish geologist Charles Lyell, who sent him molar fragments 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. Falconer found that his specimens were distinct, confirming his conclusion by examining their internal structure and studying additional molars from Mexico. Although scientists William Phipps Blake and Richard Owen believed that E. texianus was more appropriate for the species, Falconer rejected the name; he also suggested that E. imperator and E. jacksoni, two other American elephants described from molars, were based on remains too fragmentary to classify properly. 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 doubts about its adequacy as a holotype have been raised.
File:Osborn mammoth evolution.jpg|thumb|upright=2|alt=Skeleton of a mammoth with long, curved tusks|Henry F. Osborn's 1942 diagram of evolutionarily "progressive" mammoth skulls of species he grouped in the genus Parelephas; the North American species are now considered junior synonyms of M. columbi
In the early 20th century, the taxonomy of extinct elephants became increasingly complicated. In 1942, the American paleontologist Henry F. Osborn's posthumous monograph on the Proboscidea was published, wherein he used various generic and subgeneric 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.
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. In 2003, the American paleontologist Larry Agenbroad reviewed opinions about North American mammoth taxonomy, and concluded that several species had been declared junior synonyms, and that M. columbi and M. exilis were the only species of mammoth endemic to the Americas. The idea that species such as M. imperator and M. jeffersoni 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.
Evolution
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 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, and part of the distinct family Mammutidae, which diverged 25 million years before the mammoths evolved. The Asian elephant is the closest extant relative of the mammoths. The following cladogram shows the placement of the Columbian mammoth among other Late Pleistocene proboscideans, based on genetic studies:Since many remains of each species of mammoth are known from several localities, reconstructing the evolutionary history of the genus is possible through morphological studies. Mammoth species can be identified from the number of enamel ridges 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 taller in height and the skulls became taller to accommodate this. At the same time, the skulls became shorter from front to back to reduce the weight of the head. The short, tall skulls of woolly and Columbian mammoths are the culmination of this process.
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 2.0–1.7 million years ago. In turn, this species was replaced by the steppe mammoth with 18–20 ridges, which evolved in eastern Asia around 2.0–1.5 million years ago. The Columbian mammoth evolved from a population of M. trogontherii that had crossed the Bering Strait and entered North America about 1.5-1.3 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. Woolly mammoths entered North America about 100,000 years ago.
A population of mammoths derived from Columbian mammoths that lived between 80,000 and 13,000 years ago on the Channel Islands of California, away from the mainland, evolved to be less than half the size of the mainland Columbian mammoths. They are, therefore, considered to be the distinct species M. exilis, the pygmy mammoth. These mammoths presumably reached the islands by swimming there when sea levels were lower, and decreased in size due to the limited food provided by the islands' small areas. Bones of larger specimens have also been found on the islands, but whether these were stages in the dwarfing process, or later arrivals of Columbian mammoths is unknown.