An “amphibious mouse” with partially webbed feet that eats aquatic insects was among 27 new species discovered during a 2022 expedition to Peru’s Amazon, according to Conservation International.

Trond Larsen, head of Conservation International’s Rapid Assessment Program, told Reuters this week that scientists also discovered a spiny mouse, a squirrel, eight types of fish, three amphibians, and 10 types of butterflies.

He added that another 48 species found by investigators were potentially new but needed further study.

The new species were found in Alto Mayo, a protected area with several ecosystems, Indigenous territories and villages.

“Discovering so many new species of mammals and vertebrates is really incredible, especially in such a human-influenced landscape as Alto Mayo,” Larsen said.

The expedition between June and July 2022 was made up of 13 scientists plus local technicians and members of Indigenous groups.

“It was really fantastic to work so closely with the Awajun people. They have extensive traditional knowledge about the forests, animals and plants they live side-by-side with,” Larsen said.

Among the new species, Larsen highlighted the spiny mouse that has stiff fur, the amphibious mouse, and a dwarf squirrel that measures 14 cm (5.5 in).

“(The squirrel) fits so easily in the palm of your hand. Adorable and beautiful chestnut-brown color, very fast,” Larsen said. “It jumps quickly and hides in the trees.”

Another favourite discovery was the blob-headed fish, a type of armoured catfish, he said.

During the 38-day expedition, 2,046 species were recorded using camera traps, bioacoustic sensors, and DNA sampling. Of these, 49 were classified as threatened, including the yellow-tailed woolly monkey and the tree monkey.

Larsen said the discoveries reinforced the need to protect the area.

“Unless steps are taken now to safeguard these sites and help restore parts of the landscape … there’s a strong chance they won’t persist in the long term,” Larsen said.