A Rodent Like No Other – A New Indonesian Species

Just when you thought you had a grasp on mammalian diversity, nature throws you a curve. Scientists working in Indonesia have just discovered an extraordinary new species of rodent (Figure 1). It’s unlike any other rodent on Earth. It’s an almost toothless, worm-eating shrew-rat, described in Biology Letters.

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Figure 1. A photo of the new shrew-rat (Paucidentomys vermidax). (From Esselstyn et al, 2012)

One of the defining features of all rodents is the presence of paired incisors, followed by a gap called a diastema, and then a row of molar-like cheek teeth. Yet, this new rodent from Mont Latimojong, Indonesia lacks any cheek teeth, has only two upper and two lower incisors, and the upper incisors are bicuspid (similar to some shrews). “There are more than 2,200 rodent species in the world and until this discovery all had molars in the back of their mouth and incisors at the front,” said Dr. Kevin Rowe, Senior Curator of Mammals, Museum Victoria, and member of the team of scientists who discovered the new species.

Rowe and his colleagues named the new species
Paucidentomys vermidax, an apt name roughly meaning “few toothed mouse that eats worms (Figure 2). This shrew-rat is unable to gnaw or chew and its stomach contained only worms, suggesting that it ate only soft-bodied food that it could grasp with its unusual incisors.

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Figure 2. Skulls (dorsal, ventral and lateral views) and mandibles of P. vermidax (FMNH 213102). (From Esselstyn et al., 2012)

In the moist montane forests where these animals reside earthworms are abundant. Evidently, evolution lead to the loss of previously successful traits in rodent faced with new dietary opportunities.
Dr. Rowe points out that, “while we face a global crisis of biodiversity loss, this new species reminds us that we are still in an age of biodiversity discovery. Wild habitats where new species wait to be discovered are still out there. In the mountains of Sulawesi, where we discovered
Paucidentomys, healthy forests still nurture rare and remarkable species, however, they are isolated patches imperiled by expanding logging, mining, plantations and other human activities.”


References

Esselstyn, J.A., A. S. Achmadi, and K.C. Rowe. (2012) Evolutionary novelty in a rat with no molars. Biology Letters, published online, doi:10.1098/rsbl.2012.0574