Giant rats shed light on extinction

Megalomys desmarestii
Megalomys desmarestii

New research involving scientists from the Zoological Society of London (ZSL), and the Natural History Museum (NHM), has reconstructed the eventful evolutionary history of an extremely unusual and enigmatic group of extinct Caribbean rodents.

Caribbean rice rats historically lived on eastern Caribbean islands such as St Lucia, Guadeloupe, St Kitts and Nevis, where they were the only native land mammals – and some species evolved to be as big as cats. By the early twentieth century they had been wiped out by European colonists, and are now only known from bones and museum specimens.

Researchers used ancient DNA to study rice rat remains from 10 Caribbean islands, and found that the rats were unexpectedly highly diversified. The loss of the Caribbean rice rats is one of the largest mammal extinction events in the past few thousand years, and its magnitude rivals the better-known recent extinctions of Australian mammals such as the thylacine.

Dr Samuel Turvey, co-author and Senior Research Fellow at ZSL, comments: “We might not expect rodents, which are widespread, fast-breeding and adaptable, to be vulnerable to extinction. However, whilst rice rats were once found on many islands in the Caribbean and were even more diverse than we originally thought, they were not able to survive the threats caused by human activity. Their complete disappearance highlights the vulnerability of many species that have evolved on islands, and demonstrates that huge amounts of biodiversity are potentially at risk of human-caused extinction.”

Dr Selina Brace, lead author of the paper and researcher at the NHM, says: “Hot climates damage ancient DNA, so working with extinct Caribbean rodent samples was incredibly challenging. Despite the pain it was worth it when we found such an unexpected level of diversity in this group, meaning we could highlight this forgotten radiation of extinct rodents."

The full research paper is available in Proceedings of the Royal Society B.

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