Your Daily Fossil

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Mar 7

Macrauchenia

Skeleton on display at the American Musuem of Natural History, NYC. 

Reconstruction is part of the traveling exhibit Extreme Mammals which started at the American Museum of Natural History. 

When: Late Miocene to Late Pleistocene (7 million to 20,000 years ago)

Where: South America 

What: Macrauchenia is a hoofed mammal from South America. This animal has been known to science for a very long time. The first fossils were found by none other than Charles Darwin when he was traveling on the Beagle. He gathered up the fossilized  vertebra and limb bones and brought them back to England, where they were studied by Richard Owen, who coined the name Macrauchenia (meaning ‘long neck’), and supposed the whole animal would have resembled a llama. Later fossil finds, including several almost complete specimens, confirmed that Macrauchenia  did somewhat resemble a llama, with its slender legs and long neck. However, it was very diffent in some critcal areas, such as having 3 hoofed toes per foot and a mobile trunk. How do we know this animal had a trunk from just the bones? In living mammals with long trunks (such as the elephant and the tapir) the skull is transformed for the musculature that allows such a structure to move, and the skull of Macrauchenia has many features which closely match that of these modern trunked species. 

So with this long llama-like neck and the tapir-like trunk, how does Macrauchenia fit into the mammal family tree? That is a subject of much debate, but it is certain that it is not especially closely related to either artiodactyls (llamas) or  perissodactyls (tapirs).  Macrauchenia is in the order Litopterna, a group of mammals which is only found in South America. Litopterna is assuredly an order of placental mammals, but its exact placement relative to the other major clades is uncertain at this time. It has been suggested they, and other South American ungulate groups, may fall somewhere close to Afrotheria

South America  was isolated from all others for millions of years, in ‘splendid isolation’, during which time the mammals upon it radiated to fill all available niches, and this resulted in dozens of cases of convergent or parallel evolution. There are ungulate fossil froms known from South America that closely resemble not only llamas but also horses, rabbits, and even elephants! Carnivorous forms got in on the act too, such as Thylacosmilus, which looked very simular to the Saber-toothed ‘tigers’ of North America. Many South American natives went extinct during the great faunal interchange, but Macrauchenia survived until the end of the last glacial period. There is hope that one day we might recover some ancient DNA of this animal, which would be very helpful in determining where it falls in the great family tree of placental mammals.