How Settlers Wiped Out the Caribbean’s Rodents of Unusual Size

The eradication of rice rats in the Lesser Antilles was part of a massive mammal extinction event

Giant rat
A giant rice rat specimen from the National Museum of Natural History in Paris, France Public Domain via Wikimedia Commons

The loss of some large rodents may seem like something to cheer about rather than mourn, but recently scientists uncovered the story of the giant rats that used to live on the islands of the Lesser Antilles. After years of combing through the vaults of museums, researchers have recently managed to scrape together enough DNA to uncover the story of the Caribbean’s giant rats. And what they've found is that these rodents represented one of a handful of surprisingly diverse species of rice rats, Jonathan Amos for BBC News reports.

European settlers apparently thought the so-called "rice rats" were pests that threatened coconut plantations. So to keep them at bay, settlers introduced the fierce mongoose deliberately to keep their crops free of snakes and other pests. The predators, along deforestation and competition with black and brown rats that likely arrived as stowaways, drove the rice rats to extinction. The last ones died in the early 20th century, Amos explains:

Today, researchers regard what happened in the Caribbean as one of the largest mammal extinction events in the past few thousand years. Its magnitude rivals even that seen in Australia where settlers removed a great many mammals, including the thylacine, or Tasmanian tiger as it is commonly called.

"The rice rat extinction is itself a major extinction event, but it is only a component of the wider loss of mammals across the entire Caribbean basin," Sam Turvey, of the Zoological Society of London told BBC News. Turvey and his colleagues recently published the results of their genetic analysis in Proceedings of the Royal Society B

Based on the DNA they could gather, their work shows that rice rats arrived in the Lesser Antillean island chain in two distinct waves from South America. The furry newcomers probably floated in on vegetation rafts that had washed down rivers. After a while, the rats on three islands — St. Eustatius, St. Kitts and Nevis — became so genetically distinct that they might be considered different species. "This only goes to underline the scale of biodiversity loss that was initiated when human settlers arrived from Europe," Amos writes.

"It's hard to know exactly how many species disappeared across the Caribbean Basin as a whole, but there were probably in the order of over 100 different, distinct island populations of endemic mammals, of which there are maybe 7-10 left," Turvey told Amos. "A tremendous loss of mammalian biodiversity."

Today, there are several claimants to the "largest rat" title. The most commonly cited African pouched rats are in the same family as mice and rats but they come from a different branch. Still, like true rats they are smart and trainable. The kitten-sized rodents help sniff out land mines and even detect tuberculosis. 

Those animals are far more useful and less terrifying than the lumbering, ferocious "Rodents of Unusual Size" that attack Buttercup and Westley in the 1987 movie The Princess Bride. There aren’t any accounts online that recall the temperament of the extinct Caribbean rice rats, but other, still-living large rats tend to be much more pleasant than their fictional counterparts.

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