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About 11 million years ago, monkeys somehow crossed the sea from South America to the island of Jamaica in the Caribbean. There they evolved into a new species that was unlike any other known monkey. It's a striking example of how to live on an island can transform a species. The details have been revealed by DNA.
The first remains of Xenothrix mcgregori were discovered in Long Mile Cave, Jamaica in 1920. The few bones found reveal a highly unusual monkey, with relatively few teeth and legends.
"Says Ross MacPhee of the American Museum of Natural History. New York. Some extinct Madagascan lemurs also evolved a similar slow-moving lifestyle.
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Ever since it was described in 1952, X. mcgregori has been an enigma. It was related to South American monkeys, but it was unclear which group it belonged to when its ancestors reached Jamaica. Some suggestions were made based on the bones, but the monkey was so unusual it was impossible to be sure. "It's been over the place," says MacPhee.
Lorraine Meeker (American Museum of Natural History, New York)
To clear up the mystery, MacPhee and his colleagues obtained X. mcgregori bones. They recovered the whole mitochondrial genome – which animals only inherited from their mothers – and seven chunks of the nuclear genome.
The team compared these samples of DNA with the equivalent sequences from 15 different groups of South American primate. They found that X. mcgregori belonged to a group called the titi monkeys. These monkeys live in forests, eat fruit and do not have prehensile tails.
X. mcgregori does not look like a typical titi monkey, though, so on arriving on the island obviously forced its ancestors to evolve. "The selective pressures on them must have been just extreme," says MacPhee. Island species often evolve rapidly, because there are few large predators but also little fresh water.
Xenothrix split from its closest South American about 11 million years ago, suggesting that when its ancestors reached Jamaica. They must have somehow crossed the sea, perhaps a raft of vegetation.
Other primates were present in the Caribbean earlier, from about 18 million years ago. It seems several groups made the crossing at the different times, establishing a unique ecosystem. Unfortunately, most of the Caribbean species died when humans first arrived on the islands, so are only known from preserved remains.
X. mcgregori died out about 900 years ago. There is no hard evidence as to why. "What we think but can not demonstrate is that Xenothrix, like hundreds of other species, was a victim of direct or indirect impacts by the first humans who got there, "says MacPhee.
Journal reference: PNAS, DOI: 10.1073 / pnas.1808603115
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