A rodent unlike any other: Paucidentomys vermidax. Photo from: Esselstyn et al.
The Indonesian island of Sulawesi is a workshop of bizarre evolutionary experiments. Think of the babirusa, pig-like species with tusks that puncture their snouts; or the maleo, a ground-bird that lays its eggs in geothermal heated sand; or the anoa, the world’s smallest wild cattle. Now the island, made up of four intersecting peninsulas, can add another bizarre creature to its menagerie of marvels: the Paucidentomys vermidax, a new species of rodent that is different from all others.
Unlike the over 2,000 known species of rodents, Paucidentomys vermidax lacks cheek teeth, which makes it impossible for the species to gnaw on its food. So, if the rodent is not gnawing on nuts and seeds what does it eat?
“Stomach contents from a single specimen suggest that the species consumes only earthworms,” the discoverers write in a new paper in Biology Letters. The scientists speculate that the species actually lost its gnawing incisors, which in most other rodents grow continuously, allowing it to “exploit resources that were not previously available,” i.e. earthworms or other soft-tissued prey. Sporting only two teeth, think of Paucidentomys vermidax as the geriatric of the rodent family.
“With the transition to soft-bodied prey, the mouth was relieved of the need to process food by chewing, and therefore was free to evolve according to the pressures of food acquisition,” the researchers write.
Although somewhat related to shrew-rats—which are rodents and not true shrews found on Sulawesi as well as Luzon Island in the Philippines—the researchers write that Paucidentomys vermidax goes beyond even its closest relatives since it “lacks molars and possesses bicuspid upper incisors, both of which are unique among the more than 2,200 rodent species.”
Discovered in montane forests on Sulawesi’s Mount Latimojong and Mount Gandangdewata, the researchers decided the new species was unique enough to warrant its own genus: Paucidentomys, which means ‘few-tooted mouse.’ While its species name, vermidax, translates to ‘worm-devourer’.
Despite its distinctiveness, the scientists think that Paucidentomys vermidax, or few-toothed worm eater, may face competition both from other shrew-rats and from proper shrews.
The researchers don’t address conservation issues related to Paucidentomys vermidax , however the island of Sulawesi has experienced vast deforestation and forest degradation in recent decades, resulting in many of its species becoming endangered. Since it’s found in high-altitude montane forest, Paucidentomys vermidax may be at least partially protected from conversion of forests into crops.
Image of Mount Gandangdewata. Image created using Google Earth.
CITATION: Jacob A. Esselstyn, Anang Setiawan Achmadi and Kevin C. Rowe. Evolutionary novelty in a rat with no molars. Biology Letters. August, 22nd 2012. doi: 10.1098/rsbl.2012.0574.
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