Researchers in Peru’s Abiseo River National Park made a finding that expands scientific knowledge of the Andes. The UNESCO World Heritage site revealed an animal species previously undocumented: a mouse opossum in Peru.
in 2018, Silvia Pavan, a professor of biological sciences at California State Polytechnic University, Humboldt, led the expedition. She had been searching for a mysterious squirrel believed to inhabit the area. Instead, her team found something unexpected—a small marsupial unknown to science. Their findings were published in June in American Museum Novitates.
A small mammal in an unusual place
The new species was found near an archaeological site on the eastern slopes of the Andes. The animal has reddish-brown fur, dark mask-like markings on its face, and measures up to 10 inches from nose to tail, with a body length of just 4 inches.
In a groundbreaking discovery, biologists in Peru’s Río Abiseo National Park identified the tiny, big-eyed mouse opossum, named Marmosa chachapoya, a species previously unknown to science, highlighting the urgent need for conservation in this rich but vulnerable ecosystem. pic.twitter.com/mCZRpBdhdR
— unumihai Media (@unumihaimedia) September 25, 2025
Its habitat adds to the significance of the find. Unlike related species, this opossum lives at an altitude where members of its genus are not typically found. “I realized immediately that this was something unusual,” Pavan said. Only one specimen has been collected so far, and scientists have yet to learn about its natural history or distribution.
Years of scientific confirmation
Verifying the discovery required years of work. Researchers examined the opossum’s DNA and physical traits, including its elongated snout and slender build. They compared the specimen with others held in museums worldwide, carefully ensuring it had not already been identified.
The process demanded international collaboration and extensive laboratory testing. DNA sequencing confirmed what researchers suspected from the start: the mouse opossum represented a new species to science.
Honoring the Chachapoya
Pavan and her colleagues named the animal Marmosa chachapoya, in tribute to the Chachapoya culture that thrived in the Andes before the arrival of the Inca and later European colonization.
The opossum was not the only discovery. The expedition also recovered several other animals, including a semi-aquatic rodent that has not yet been formally described.
Conservation significance
The discoveries underscore the region’s role as a biodiversity reservoir. Pavan said the findings reveal the extent of the undocumented species in the Andes and suggest that many remain to be identified. Without conservation efforts, some could face threats before they are even recognized by science.
“It’s a reminder of the critical importance of scientific exploration and conservation in areas like Río Abiseo,” she said.
The discovery of Marmosa chachapoya highlights both the biological richness of Peru’s Andes and the gaps that remain in understanding its wildlife. For scientists, it shows that even in protected areas, the natural world continues to hold hidden surprises.
