Some 11 million years ago, small arboreal primates closely related to the modern-day titi monkey found themselves stranded on makeshift rafts of vegetation floating from the mouths of large South American rivers to islands across the Caribbean. Those that landed in Jamaica followed an unusual evolutionary path guided by the unique constraints of island living, eventually transforming into creatures with few teeth; short, rodent-like legs; squat bodies similar to that of the slow loris; and a relaxed, sloth-like lifestyle.
It’s been 900 or so years since these primates—officially known as Xenothrix mcgregori—last lounged in Jamaica’s tropical trees, but thanks to a new DNA analysis published in the Proceedings of the National Academy of Sciences, we now know more about them than ever before.
X. mcgregori has baffled scientists since 1920, when researchers discovered pieces of its skull and teeth in Jamaica’s Long Mile Cave. Additional samples, including skulls, leg bones and jaws, have popped up over subsequent decades, George Dvorsky writes for Gizmodo, but the singularity of the primate’s appearance made its origins and exact lineage difficult to trace.
Now, New Scientist’s Michael Marshall reports, scientists from New York’s American Museum of Natural History (AMNH), London’s Natural History Museum and the Zoological Society of London have extracted DNA from two X. mcgregori bones to map out the animal’s mitochondrial (inherited only from maternal lineage) and a portion of their nuclear genome. And, after comparing these samples to the DNA of 15 groups of South American primates, the team has determined that X. mcgregori was actually a type of titi monkey—small, territorial tree-dwellers that roam the South American forests to this day—rather than an entirely unique phylum.
Ross MacPhee of the AMNH’s mammalogy department explains that the Jamaican monkey likely owes its odd evolution to environmental factors.
“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,” he says in a statement. “Evolution can act in unexpected ways in island environments, producing miniature elephants, gigantic birds, and sloth-like primates.”
According to New Scientist’s Marshall, islands encourage rapid evolution because they tend to host few large predators, enabling animals like X. mcgregori to adopt a slower pace of life. At the same time, islands offer little drinking water, forcing residents to compete for this scarce resource. As Gizmodo’s Dvorsky notes, island environments have been shown to foster the rise of unusual creatures such as miniature elephants, “Hobbit” humans, and enormous birds and rats.
Prior to this study, scientists had little reason to draw connections between the odd Jamaican primate and titi monkey, Dyani Lewis writes for Cosmos. Most variations amongst titi species are limited to size and fur color, which is typically red, brown, grey or black. The key to the primates’ relationship, then, lies not in their divergent appearances, but their common point of origin.
By the 1700s, X. mcgregori had largely vanished from the Jamaican tropics. And, MacPhee tells New Scientist, the likely culprit behind this disappearance is the same one cited in the extinction of most of the Caribbean’s native species: humans.
As MacPhee concludes, “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.”