Weird Monkey Turned Into a Sloth-like Creature After Arriving in Jamaica 11 Million Years Ago

Xenothrix's close relative, the red titi monkey (Callicebus cupreus). ZSL

An international team of scientists has extracted the DNA of a mysterious extinct monkey, casting new light on its murky evolutionary history. Until relatively recently, the Caribbean contained a remarkable evolutionary branch of now-extinct mammals, including several highly unusual primates—the strangest of which was the Jamaican monkey (Xenothrix mcgregori).

This animal, unlike any other living monkey, was a slow-moving tree-dweller—much like today's sloths—with relatively few teeth and leg bones similar to those of rodents.

Efforts to determine what it was related to and how it evolved have been challenging due to its strange characteristics, in addition to the lack of complete fossils and well-preserved DNA in ancient tropical samples.

But now, a team from ZSL (Zoological Society of London), London's Natural History Museum (NHM), and the American Museum of Natural History in New York have successfully extracted DNA from the bones of a Xenothrix specimen discovered in a Jamaican cave, finding that it is closely related to a group of New World monkeys known as titis, which are found across tropical South America.

Previously, it was thought that Xenothrix may have represented a whole new branch of New World monkey that are only distantly related to titis.

The latest study, published in the journal Proceedings of the National Academy of Sciences, represents the first time that scientists have successfully extracted DNA from an extinct Caribbean primate, providing fascinating new insights into this group of animals.

"Recovering DNA from the bones of extinct animals has become increasingly commonplace in the last few years," Ian Barnes, a co-author of the study at the NHM's ancient DNA lab, said in a statement.

"However, it's still difficult with tropical specimens, where the temperature and humidity destroy DNA very quickly. I'm delighted that we've been able to extract DNA from these samples and resolve the complex history of the primates of the Caribbean."

According to the researchers, Xenothrix's ancestors likely colonized Jamaica from South America around 11 million years ago, probably after being stranded on natural rafts of vegetation that were washed out of the mouths of large rivers—a similar process to how many other animals are thought to have first made their way to the Caribbean islands.

The analysis of Xenothrix's DNA reveals that the species then underwent drastic evolutionary changes as a result of the island's unique environment, which meant that over time their bodies began to look very different to titi monkeys. The date of the split between Xenothrix and other titis also reveals that primates must have colonized the Caribbean more than once.

"Ancient DNA indicates that the Jamaican monkey is really just a titi monkey with some unusual morphological features, not a wholly distinct branch of New World monkey," Ross MacPhee from the American Museum of Natural History's Mammalogy Department, a co-author of the study, said in the statement.

"Evolution can act in unexpected ways in island environments, producing miniature elephants, gigantic birds, and sloth-like primates. Such examples put a very different spin on the old cliché that 'anatomy is destiny.'"

According to Samuel Turvey, another co-author of the study from ZSL, this new understanding of the evolutionary history of Xenothrix demonstrates that evolution can take unexpected paths when animals colonize islands and are exposed to new environments.

"However, the extinction of Xenothrix, which evolved on an island without any native mammal predators, highlights the great vulnerability of unique island biodiversity in the face of human impacts," he said.

The Caribbean islands have hosted some of the most unusual and mysterious species ever to have evolved, however, the region has also experienced the world's highest rate of mammal extinction since the end of the last ice age. Humans have been blamed for this high rate of extinction due to the effects of habitat loss, hunting and predation by invasive mammals brought by settlers.