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'Really Just a Titi Monkey'

Scientists have been arguing about the evolutionary origins of an extinct monkeyXenothrix mcgregori, for nearly 100 years, Gizmodo reports. It lived in Jamaica for thousands of years before going extinct, and scientists first found samples of its teeth and skull in the 1920s. Since then, they've found some leg and jaw bones that have suggested some odd features, and this has caused a debate: is it a different species than any other monkey on the planet or not?

Because it lived in Jamaica, Xenothrix didn't have a lot of predators, Gizmodo says, adding, "It had weirdly rodent-like legs, relatively few teeth, and a body plan similar to the loris. This small monkey was likely a tree-dweller, moving slowly from branch to branch like a shrunken sloth." And in addition to the unusual morphology, scientists struggled to obtain DNA from the bones because the high temperatures and humidity had destroyed much of what was left in the samples. 

Now, a new study in PNAS has pulled the evolutionary origins of this rodent-loris-sloth-monkey into sharper focus. Genetic analysis of four Xenothrix specimens found in Jamaican caves suggests it's "really just a [South American] titi monkey with some unusual morphological features, not a wholly distinct branch of New World monkey," Ross MacPhee, a co-author of the study and a scientist at the American Museum of Natural History's Mammalogy Department, said in a statement.
The monkeys likely arrived in Jamaica by clinging to rafts of floating vegetation, Gizmodo reports, and then underwent body modifications through years of evolution in order to adapt to their new environment. And the samples the scientists worked from for this study date to 1,400 to 900 years ago, so those monkeys likely lived alongside human settlers. The genetic analysis suggests the ancestors of Xenothrix arrived to Jamaica around 11 million years ago, but probably came on multiple occasions. 

Importantly, Gizmodo adds, the study shows how an animal can evolve when exposed to a new environment. Further, the article quotes study co-author Samuel Turvey, who noted that Xenothrix's extinction "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 researchers aren't sure how or why Xenothrix went extinct, but hunting and loss of habitat likely played a part, Gizmodo says.