Macrauchenia

Macrauchenia ("long llama", based on the now-invalid llama genus, Auchenia, from Greek "big neck") is an extinct genus of large ungulate native to South America from the Pliocene or Middle Pleistocene to the end of the Late Pleistocene. It was one of the last surviving members of the extinct order Litopterna, a group of South American native ungulates distinct from the two orders which contain all living ungulates which had been present in South America since the early Cenozoic, over 60 million years ago, prior to the arrival of living ungulates in South America around 2.5 million years ago as part of the Great American Interchange. The bodyform of Macrauchenia has been described as similar to a camel, being one of the largest-known litopterns, with an estimated body mass of around 1 tonne. The genus gives its name to its family, Macraucheniidae, which like Macrauchenia typically had long necks and three-toed feet, as well as a retracted nasal region, which in Macrauchenia manifests as the nasal opening being on the top of the skull between the eye sockets. This has historically been argued to correspond to the presence of a tapir-like proboscis, though recent authors suggest a moose-like prehensile lip or a saiga antelope-like nose to filter dust are more likely.

Only one species is generally considered valid, M. patachonica, which was described by Richard Owen based on remains discovered by Charles Darwin during the voyage of the Beagle. M. patachonica is primarily known from localities in the Pampas, but is known from remains found across the Southern Cone extending as far south as southernmost Patagonia, and as far north as Southern Peru. Another genus of macraucheniid Xenorhinotherium was present in northeast Brazil and Venezuela during the Late Pleistocene.

Macrauchenia is thought to have been a mixed feeder that both consumed woody vegetation and grass that lived in herds and probably engaged in seasonal migrations. Macrauchenia is suggested to have been a swift runner that was capable of moving at considerable speed. The large sabertooth cat Smilodon populator may have been an important predator.

Macrauchenia became extinct as part of the end-Pleistocene extinction event around 12,000 years ago, along with the vast majority of other large mammals native to the Americas. This followed the arrival of humans to the Americas, and possible evidence of butchery of Macrauchenia has been found at a number of sites, with human hunting suggested to have possibly played a role in its extinction.

Macrauchenia fossils were first collected on 9 February 1834 at Port St Julian in southern Patagonia in what is now Argentina by Charles Darwin, when HMS Beagle was surveying the port (the Argentine Confederation claimed the region but did not effectively control it at the time). As a non-expert he tentatively identified the leg bones and fragments of spine he found as "some large animal, I fancy a Mastodon". In 1837, soon after the Beagle's return, the anatomist Richard Owen identified the bones, including vertebrae from the back and neck, as from a gigantic creature resembling a llama or camel, which Owen named Macrauchenia patachonica. In naming it, Owen noted the original Greek terms µακρος (makros, large or long) and αυχην (auchèn, neck), as used by Illiger as the basis of Auchenia as a generic name for the llama, Vicugna and so on.

Macrauchenia patachonica is currently considered to be the only valid species of Macrauchenia. Macrauchenia boliviensis from the probably early Miocene aged Kollukollu Formation of Bolivia described by Thomas Henry Huxley in 1860 is now considered to be an indeterminate member of Macraucheniidae. The species Macrauchenia ensenadensis described by Florentino Ameghino in 1888 from the Early Pleistocene has been transferred to the closely related genus Macraucheniopsis.

Macrauchenia is part of the extinct ungulate order Litopterna, which is grouped with several other orders as part of the South American native ungulates (SANUs), which formed a conspicuous element of South America's Cenozoic mammal fauna beginning during the Paleocene, over 60 million years ago. Litopterns generally have body forms similar to those of living ungulates.

The relationships of litopterns (as well as other SANUs) to living mammals was historically uncertain. Sequences of mitochondrial DNA extracted from remains of M. patachonica found in a cave in southern Chile published in 2017 indicates that the closest living relatives of Macrauchenia (and by inference, Litopterna) are members of the extant ungulate order Perissodactyla (which includes the equids, rhinoceroses, and tapirs), with litopterns estimated to have genetically diverged from perissodactyls around 66 million years ago. Analysis of collagen sequences obtained from Macrauchenia and the contemporaneous large rhinoceros-like South American ungulate Toxodon, which belongs to another SANU order, Notoungulata, in 2015 reached a similar conclusion and suggests that litopterns are more closely related to notoungulates than to perissodactyls.