Scientists Solve The Mystery Of The ‘Weird’ Monkey That Colonized The Caribbean 11 Million Years Ago

Known as the 'Xenothrix' fossil, this now-extinct primate was unlike any other monkey living today.

Photo of a Lucifer titi monkey (Callicebus lucifer).
LABETAA Andre / Shutterstock

Known as the 'Xenothrix' fossil, this now-extinct primate was unlike any other monkey living today.

Some 11 million years ago, a group of monkeys settled on the island of Jamaica in the Caribbean. With no natural predators in sight, the monkeys were able to simply kick back and enjoy a relaxed Caribbean life. Their care-free lifestyle allowed these monkeys to thrive — they led a peaceful existence on the island up until a few hundred years ago when they suddenly went extinct — but also left a striking mark on their appearance.

Known as Xenothrix mcgregori, these Caribbean primates went on to evolve into a peculiar species that bore little resemblance to any other monkey species living today. In fact, Xenothrix mcgregori looked more like a sloth than an actual monkey, notes New Scientist.

First described in 1952, Xenothrix mcgregori had relatively few teeth and unusual leg bones that were more similar to those of a rodent than to leg bones designed for “monkey-like” locomotion, such as leaping from branch to branch and running through treetops.

“It was a really weird animal indeed,” Prof. Samuel Turvey from the Zoological Society of London (ZSL) told the BBC. “Possibly with legs like a rodent; body maybe like a slow loris. Because it’s so weird no-one’s been able to agree what it was related to.”

The remains of the now-extinct Caribbean monkey — originally discovered in a Jamaican cave in 1920 — revealed that this bizarre species grew to adapt to a slow-paced life in the tree canopy.

“What they suggest is a very slow-moving, perhaps even sloth-like lifestyle, which is perhaps not unexpected in an animal living on an island with few predators other than large birds,” says Ross MacPhee of the American Museum of Natural History (AMNH) in New York.

To figure out the history of this perplexing tree-dweller, AMNH scientists teamed up with researchers from the ZSL and the Natural History Museum in London, U.K., and examined the Xenothrix fossil. The team successfully extracted the ancient DNA of this mysterious extinct monkey and finally figured out where it came from, reports Science Daily.

Their study, published yesterday in the journal Proceedings of the National Academy of Sciences, uncovered that the peculiar Jamaican monkey had roots in South America and was actually closely related to the titi monkey (Callicebinae) — a small, tree-dwelling monkey that still lives in the tropical forests of the Amazon.

Photo of two red titi monkeys.
Red titi monkeys (‘Callicebus cupreus’). Edwin Butter / Shutterstock

Titi monkeys come in several varieties — they have long, soft fur that can be red, black, or grey — and don’t have a prehensile tail. These monkeys feed on fruit and can live for up to 12 years in the wild, with the males of the species often caring for the young.

The team believes that Xenothrix mcgregori used to be a titi monkey that got to Jamaica probably on floating vegetation and went through a remarkable evolutionary change after colonizing its new environment.

“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,” said MacPhee, who is a scientist at the AMNH’s Mammalogy Department. “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.'”

Since no living descendants of Xenothrix mcgregori survive to this day, we can only speculate on what this species looked like when it was still alive. Some researchers suggest that the Caribbean primate could have looked like a kinkajou (Potos flavus) or a night monkey (Aotus azarae).

Image of 'Potos flavus' (left) and 'Aotus azarae' (right).
Image of ‘Potos flavus’ (left) and ‘Aotus azarae’ (right). Ondrej Prosicky and Salparadis / Shutterstock

This monkey species went extinct some 900 years ago, most likely due to hunting and habitat loss. Invasive mammals brought to the island by Jamaica’s early settlers might have also preyed on Xenothrix mcgregori, possibly contributing to the species’ demise.

“What we think but cannot demonstrate is that Xenothrix, like hundreds of other species, was a victim of either direct or indirect impacts by the first humans who got there,” says MacPhee.

Prof. Turvey notes that the extinction of this species, which lived for millions of years on an island where it had nothing to fear until the arrival of man, paints a grim picture of the fate that befell many Caribbean species that are no longer here and are only known from fossilized remains.

“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.”