New Species Of Bizarre Aquatic Mouse Is Relative Of World's Rarest Rodent

Known as stilt mice, they use their long legs to wade in the water. (C) Velizar Simeonovski, Field Museum

Almost 100 years ago a strange mouse was retrieved by scientists from a stream in Ethiopia that had water-resistant fur and long, clown-like feet. The semi-aquatic creature surprised its captors as very few rodents in Africa exhibit adaptations fit for a watery lifestyle. Over 90 years later the specimen remains the only one of its genus ever collected and can be witnessed by those fortunate enough to have access to Chicago’s Field Museum where it's housed. As one of the rarest animals ever described, it’s thought the stream-dwelling mouse is now extinct but new research published in the Zoological Journal of the Linnean Society has verified some of its closest cousins, including two species new to science.

The study looked at two genera of mice, Nilopegamys and Colomys. Nilopegamys, which means "mouse from the source of the Nile" is our lone specimen holed up in Chicago while Colomys is an easier-to-come-by genus found throughout the Congo Basin. Translating roughly to “stilt mouse,” Colomys also sports elongated feet which are fit for wading in shallow streams. Here they hunt for water-dwelling insects, stood up on their haunches like a kangaroo. For a small rodent, they have surprisingly large brains that allow them to process the sensory overload experienced when fishing with sensitive whiskers in running water.

Museum specimen of  C. goslingi on the left, and the new species C. lumumbai on the right. (C) Giarla et al

While not as rare as Nilopegamys, catching Colomys is no mean feat. They’re fast-moving and occupy hard-to-access areas, not to mention that streams are hot spots for having traps swept away when the torrential tropic rain hits. Following some fraught expeditions to try and gather data on these animals in the wild, the study combined new information with museum collections and carried out DNA analyses. These investigations revealed two new species within the Colomys genus, C. lumumbai and C. wologizi, named after the Congolese independence leader Patrice Lumumba and Liberia's Wologizi Mountains respectively.

The researchers were even able to glean some DNA from the dried tissues of the 93-year-old Nilopegamys specimen to compare against their new data. Working with such an old specimen requires special treatment, as “antique DNA” such as this can very easily become contaminated. Amazingly, the team got it to work on their first try and confirmed that Nilopegamys is indeed a sister genus to Colomys, its closest relative.

"These two groups of mice have been confused with one another for a century," said  Julian Kerbis Peterhans, Field Museum researcher and one of the paper's authors, in a statement. "They've been so elusive for so long, they're some of the rarest animals in the world, so it's exciting to finally figure out their family tree.”

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