Columbian mammoth

The Columbian mammoth (Mammuthus columbi) is an extinct 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 Mammuthus subplanifrons in the early Pliocene. The Columbian mammoth evolved from the steppe mammoth, which entered North America from Asia about 1.5 million years ago. The pygmy mammoths of the Channel Islands of California evolved from Columbian mammoths. The closest extant relative of the Columbian and other mammoths is the Asian elephant. Reaching 4 m (13 ft) at the shoulders and 10 tonnes (22,000 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 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 Paleoamericans – the first humans to inhabit the Americas – 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 artifacts; these remains may have stemmed either from hunting or scavenging. The Columbian mammoth disappeared at the end of the Pleistocene around 11,500 years ago, most likely as a result of habitat loss caused by climate change, hunting by humans, or a combination of both. The Columbian mammoth was first scientifically described in 1857 by 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 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 (then Elephas primigenius). 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 (which is cataloged as specimen BMNH 40769 at the British Museum of Natural History) was reported in 2012, and could help shed more light on that specimen, since doubts about its adequacy as a holotype have been raised. In the early 20th century, the taxonomy of extinct elephants became increasingly complicated. In 1942, paleontologist Henry Fairfield 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, paleontologist Larry Agenbroad reviewed opinions 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. 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. The Asian elephant (Elephas maximus) is the closest extant relative of the mammoths. The following cladogram shows the placement of the Columbian mammoth among other proboscideans, based on characteristics of the hyoid bone in the neck: 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 (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 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.