Before European arrival, Jamaica, Cuba, and Hispaniola were home to several monkey species. The fossils of these lost primates of the Caribbean have puzzled zoologists, with conflicting theories of how they fit into the monkey family tree. Newly recovered DNA has shown the extinct Jamaican monkey Xenothrix mcgregori was closely related to South American Cheracebus, a genus of titi monkeys, but evolved dramatically once it got to the island.
Islands fast-track evolution. Island clusters like the Galapagos can lead to stunning diversity as lifeforms evolve in different directions in semi-isolation. However, few mammals made it to ocean archipelagos prior to humans providing transport. Consequently, we know little about how our fellow furred creatures respond to these environments.
This has made the Caribbean's monkeys, thought to have reached the islands by rafting on vegetation, just as their ancestors did between continents, a topic of particular interest. Xenothrix is a particularly intriguing example. We are used to monkeys being speedy creatures, but Xenothrix's body and teeth indicate it was a slow-moving tree-dweller, although unlike sloths it fed on fruit, not leaves.
Professor Samuel Turvey of the Zoological Society of London has extracted DNA from Xenothrix bones for the first time. In Proceedings of the National Academy of Sciences Turvey and co-authors report the DNA suggests Xenothrix's ancestors split from South American titi monkeys 11 million years ago, presumably around the time they arrived on Jamaica.
Xenothrix had confused zoologists previously because of features such as its small size, lack of a third molar, and leg bones like rodents. Further complicating the question of where to place it was its differences from other Caribbean monkeys, which were expected to be its nearest relatives.
However, Turvey and co-authors have concluded monkeys colonized the islands at least twice, with Xenothrix no more closely related to Caribbean monkeys from the earlier migration than it was to many mainland species. Upon arriving on territory with few competitors, the monkeys grabbed a variety of evolutionary niches and radically changed their body shapes to suit.
“This new understanding of the evolutionary history of Xenothrix shows that evolution can take unexpected paths when animals colonize islands and are exposed to new environments,” Tovey said in a statement. “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”
The animals of the Caribbean suffered many extinctions when humans arrived several thousand years ago, and again with European colonization. Between these two, the region has suffered the highest rate of post-glaciation mammalian extinction in the world. With specimens dating to just 900 years ago, it seems likely Xenothrix was a victim of the second wave.