‘Slender Root Rat’ Among 2017 Top 10 New Species

Only mammal on the list exhibits unique evolutionary reversal


Root Rat

"Slender Root Rat" is one of the four species from one mountain on Sulawesi Island, Indonesia LSU Curator of Mammals Jake Esselstyn's research team has described. The root rat is among the International Institute for Species Exploration's top 10 new species of 2017.Photo Credit: Kevin Rowe, Museums Victoria

BATON ROUGE – LSU Museum of Natural Science Curator of Mammals Jake Esselstyn is part of a team that described one of the International Institute for Species Exploration’s Top 10 New Species of 2017. Esselstyn and his colleagues have discovered a new genus and species of rodent on the island of Sulawesi in Indonesia. The rodent, nicknamed the “slender root rat,” is the only mammal on this year’s list, which is announced annually to commemorate the birthday of 18th century botanist Carolus Linnaeus, or the “father of taxonomy.”

The root rat, or Gracilimus radix, is a small, delicate mouse that looks like a cross between a mouse and a shrew rat. The root rat differs from other species of rats particularly because of its dietary habits. Shrew rats, the root rat’s closest relative, are carnivorous creatures that mainly feed on insects and earthworms. By studying stomach contents of this new species, however, Esselstyn and his colleagues discovered that the root rat is surprisingly an omnivorous animal.

“When diets change over evolutionary time, they tend to change from omnivorous to carnivorous in rats, but it doesn’t usually go back except in this one case,” Esselstyn said. “It’s difficult once you are a specialist species to evolve in a way that makes you a generalist again.”

Esselstyn, who is also an assistant professor in the Department of Biological Sciences, has been at LSU since 2013. He has conducted fieldwork in Indonesia every year since 2010 and has also conducted research in Malaysia and the Philippines. Island systems, Esselstyn said, provide the perfect environment for studying biodiversity because they contain many species that are only native to one island or a smaller region within an island. The root rat is the fourth species to be described by Esselstyn’s team from just one mountain on Sulawesi.

“Most people in society don’t realize that biodiversity is not well documented,” Esselstyn said. “There are literally millions of species that have not yet been discovered.”

Esselstyn and his colleagues will continue to study the root rat to research how this particular species fits in with the broader category of rats. He said they will use this new discovery to conduct research on the genomic, morphological and dietary diversity of the entire group of rodent species.

This is the 10th annual list identified by the State University of New York College of Environmental Science and Forestry, or ESF.

“During the decade since our first Top 10 list, nearly 200,000 new species have been discovered and named. This would be nothing but good news were it not for the biodiversity crisis and the fact that we’re losing species faster than we’re discovering them,” said ESF President Quentin Wheeler, who is founding director of the International Institute for Species Exploration. “The rate of extinction is 1,000 times faster than in prehistory. Unless we accelerate species exploration we risk never knowing millions of species or learning the amazing and useful things they can teach us.”


Additional Links:
ESF Lists Top 10 New Species for 2017: http://www.esf.edu/communications/view.asp?newsID=5863

A new genus and species of omnivorous rodent (Muridae: Murinae) from Sulawesi, nested within a clade of endemic carnivores, Journal of Mammology:


Not Your Everyday Rats, The Pursuit: LSU College of Science Blog:



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Valerie Derouen
LSU Museum of Natural Science