Research using ancient DNA has allowed a team of scientists led by Museum Curator Ross MacPhee to firmly establish the relationships of one of the strangest mammals in the known South American fossil record. Their study of this unusual species, Macrauchenia patachonica, was published today in the journal Nature Communications.
“Macrauchenia was the last of its kind, part of a hugely successful group of ungulates that had ranged over much of South America for tens of millions of years. One of its early relatives even made it to what is now part of Antarctica,” says MacPhee.
Charles Darwin found the first fossils of Macrauchenia in southern Argentina in 1834, while on the five-year voyage of the H.M.S. Beagle. Sensing its importance, he gave the material to the renowned British paleontologist Richard Owen for study and description. But Owen found the animal’s unusual mix of physical features so puzzling he could not identify it.
Weighing as much as 1,100 pounds, Macrauchenia patachonica was long-necked, with a body shape vaguely reminiscent of a camel’s. Its most distinguishing trait was its weirdly placed nasal opening, situated high on the skull, between the eye sockets. To some scientists, this feature suggested an elephant-like trunk.
Since morphology hadn’t solved the riddle of Macrauchenia’s relationships, the team came up with the solution of using ancient mitochondrial DNA, extracted from an 11,000-year-old Macrauchenia fossil found in a cave in southern Chile.
Because of its damaged condition, ancient DNA generally requires researchers to use the genomes of a species’ close evolutionary relatives to fill in gaps. In this case, though, there was a big problem with this tried-and-true method, as Macrauchenia doesn’t have any close living relatives.
Instead, the team developed a new technique that utilizes the genetic codes of numerous living species as reference points, allowing them to reliably predict the fossil’s likeliest genetic sequences.
The new technique permitted recovery of almost 80 percent of the predicted mitochondrial genome of Macrauchenia. That proved to be enough information to place it in its proper phylogenetic position as a member of the larger grouping now called Panperissodactyla, which includes living species like horses, rhinos, and tapirs.