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These Semi-Aquatic Mice Are as Fascinating as They Are Adorable

Artist’s depiction of Colomys lumumbai, one of two newly described species of semi-aquatic mice.

Artist’s depiction of Colomys lumumbai, one of two newly described species of semi-aquatic mice.
Illustration: Velizar Simeonovski, Field Museum

African rainforests are home to some of the most delightful and surprising species on Earth, as demonstrated by recent research into some rather unusual water-loving rodents.

A study published today in the Zoological Journal of the Linnean Society describes two species of semi-aquatic mice. Living in the Congo Basin and the western parts of equatorial Africa, these mice make a living by hunting insects and tadpoles while wading through shallow water.

The authors of the new study, led by biologist Tom Giarla from Siena College in New York, did a deep dive into an enigmatic genus of mouse known as Colomys, which translates to “stilt mouse” on account of their elongated feet.

Two of Giarla’s collaborators on the project, Terry Demos and Julian Kerbis Peterhans from the Field Museum in Chicago, had been doing field work in Africa for decades, and they told him about a rather odd species of rodent they had been catching near streams and swamps in central Africa—a rodent known as Colomys goslingi.

“Based on limited previous research, it purportedly had an enormous range, with scattered collecting records extending from Liberia all the way to Kenya and south to Angola,” explained Giarla in an email. “Immediately, we suspected that this one species might actually comprise several species, because few tropical rodents have such a wide natural range.”

Specimens of the stilt mice studied in the new paper. The previously known species C. goslingi is on the left, and the newly described species C. lumumbai is on the right.

Specimens of the stilt mice studied in the new paper. The previously known species C. goslingi is on the left, and the newly described species C. lumumbai is on the right.
Image: T. C. Giarla et al., 2020

To get a better handle on Colomys, the scientists took a look at the relevant field work, collected physical specimens from museum collections, and took samples of DNA. The comparative analysis resulted in the identification of four distinct species belonging to Colomys, two previously known and two unknown to science.

One of the known species, C. eisentrauti, was elevated from a subspecies to a full-blown species of its own, and its habitat was defined as being restricted to northwest Cameroon. The other known species, C. goslingi, was found to have a more restricted range than previously thought. The two newly described species were named C. lumumbai and C. wologizi, in honor of Congolese independence leader Patrice Lumumba and Liberia’s Wologizi Mountains.

The authors also took this opportunity to study a strange mouse specimen found in Ethiopia back in 1927. This creature was previously assigned to an entirely new genus and species, Nilopegamys plumbeus, and it’s probably extinct. The lone specimen exhibited characteristics similar to those seen on the stilt mice, such as water-resistant fur and elongated feet, but scientists hadn’t been able to figure out where it fit within the evolutionary family tree of rodents.

“Thanks to the curators at the Field Museum, where the only