Scientists have identified a new species in the marsupial genus Marmosa from a single specimen collected on the eastern side of the Andes in San Martín department, Peru.
Marmosa chachapoya. Image credit: Pedro Peloso.
Marmosa is a genus of relatively small Neotropical mammals in the family Didelphidae.
It is one of three genera that are known as mouse opossums; the others are Thylamys and Tlacuatzin.
“Marmosa is the most speciose genus of American marsupials, including 26 species in five subgenera that occur in a wide range of tropical and subtropical habitats from Mexico to Argentina,” said California State Polytechnic University’s Professor Silvia Pavan and her colleagues.
“In addition to named species of Marmosa, two putative new species from northern Peru were recently indicated by a phylogenetic analysis: one was recovered as a member of the subgenus Stegomarmosa, whereas the other nested among species in the subgenus Micoureus.”
The new Marmosa species was discovered at an altitude where other species of this genus are not typically found.
Named Marmosa chachapoya, the animal has reddish-brown fur, distinct mask-like markings on its face.
It has a total length — including body and tail — of up to 25 cm (10 inches); the body alone measures only about 10 cm (4 inches).
According to the researchers, Marmosa chachapoya is closely related to two species in the subgenus Stegomarmosa: Marmosa lepida and Marmosa andersoni.
“I realized immediately that this was something unusual,” Professor Pavan said.
“We know very little about this species, including its natural history and distribution, and only one specimen has been collected so far.”
To confirm it was a new species, the scientists studied its DNA and physical features, focusing on distinctive traits such as the elongated snout and delicate body.
“Marmosa chachapoya isn’t the only new species discovered during the expedition,” Professor Pavan said.
“We collected several others — including a new semi-aquatic rodent — which have yet to be formally described.”
“These discoveries are particularly significant for biodiversity and conservation efforts, underscoring how much remains unknown about the biodiversity of this region.”
“The findings also suggest that it’s home to more species yet unknown to science, many of which could be vulnerable without protection.”
“It’s a reminder of the critical importance of scientific exploration and conservation in areas like Río Abiseo.”
The team’s paper was published on June 19, 2025 in the journal American Museum novitates.
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Silvia E. Pavan et al. 2025. A new species of Marmosa (Mammalia, Didelphimorphia, Didelphidae) from Parque Nacional del Río Abiseo, Peru. American Museum novitates 4037
