DNA Reveals Caribbean "Island Murderer" Lineage Emerged As Dinosaurs Bit The Dust

The recovered island murderer skull. James McNish/NHM

Once upon a time, hundreds of years ago, there lived a creature known as an “island murderer”. This terrifying West Indian mammal, spread across the prehistoric Caribbean, used to feast on its unwitting prey with an unrelenting furiousness right up to its recent extinction in the 16th century.

Admittedly, the pseudonym doesn’t live up to this creature’s actual appearance and behavior. It was shrew-sized, its food consisted of tiny insects, and it died out when it was outcompeted by rats arriving with Spanish conquistadors. As a new study points out, though, there is a lot about this master of false advertising that’s still unknown, including where it came from in the first place or what it was closely related to.

Writing in the journal of Molecular Biology and Evolution, a team of researchers have managed to trace its evolutionary history back to an ancestral group that lived 70 million years ago, at the dawn of the first mammals and the twilight age of the non-avian dinosaurs. Unlike the lumbering beasts of yore, this mammal lineage was one of only 7 percent that survived the spaceborne apocalypse.

Then, about 40 million years ago, this ancient group of mammals diverged into two distinct families. The Nesophontidae (“island murderers”) appeared alongside Solenodontidae, a similar but still-living family of venomous, nocturnal, burrowing curiosities.

Significantly, the Nesophontidae family of mammals were the only remaining group not to have their origin and evolutionary history uncovered. This study, then, has finally filled in the missing piece of the jigsaw puzzle, and our understanding of mammalian evolution in the last few tens of millions of years now includes every single mammal lineage.

Taking the remains of a 750-year-old Hispaniolan Nesophontes paramicrus specimen, the team managed to analyze its genome. Comparing it to its living cousins, they discovered that it had a considerably older origin point than they expected.

It appears that the divergence between the two lineages took place when the northern Caribbean was comprised of newly formed volcanic islands. As new landmass emerged, two populations could have become geographically segregated, and each could have taken a different evolutionary path.

Conversely, it’s also possible that there was no separation, and two groups evolved within the same population to hunt different types of prey.

Image in text: An artist's impression of the extinct critters. Jennifer Garcia/Wikimedia Commons; CC BY-SA 3.0

Locating a Nesophontes specimen fresh enough to allow for the extraction of any intact DNA is incredibly difficult. Samples are difficult to find and highly weathered at the best of times. This team got lucky when they found a skull of one of these island murderers within a pile of extremely old owl droppings.

“Once we'd dealt with the tiny size of the bone samples, the highly degraded state of the DNA, and the lack of any similar genomes to compare to, the analysis was a piece of cake,” lead author Dr Selina Brace, a palaeogeneticist at London’s Natural History Museum, said in a statement.

Sadly, the fact that this lineage is so old also means that its 16th century extinction is a testament to how fast, and how negatively, human activity is affecting the world’s biodiversity.

“The insular Caribbean has lost <100 endemic mammal species or island populations through anthropogenic activities, representing the world’s highest levels of Holocene and historical era mammal extinction,” the team write.

“The complete loss of Nesophontidae in recent times, together with the disappearance of most or all representatives of other ancient Caribbean mammal groups such as sloths, primates and capromyid rodents, unfortunately highlights the magnitude of ongoing human-induced loss of mammalian evolutionary history.”

Looks like we’re the island murderers after all, then.

Image in text: A Hispaniolan solenodon. Seb az86556/Wikimedia Commons; CC BY-SA 3.0

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