New species of mouse opossum discovered that has a tail longer than its body

A peer-reviewed report has documented a new animal species – a small marsupial, found at 8,740 feet (2,660 meters) in the eastern Andes of Peru. Turns out this is not just a variant of something already known, but a new species in its own right.

The animal was collected inside Río Abiseo National Park, which is a UNESCO World Heritage site. The Park protects cloud forests, high grasslands, and a trove of archaeological heritage.

The new marsupial, Marmosa chachapoya, is a mouse opossum and belongs to a group that is represented by many species across the Americas.

Discovering Marmosa chachapoya

The work was led by Silvia E. Pavan, museum curator at Cal Poly Humboldt, in collaboration with colleagues in Peru and the American Museum of Natural History (AMNH).

Her team documented the specimen’s features and sequenced specific DNA regions to test whether they matched any named species.

The holotype was captured in 2018, in an upper montane rainforest site within the Park. Rather than rely on a glance and a hunch, the researchers paired careful measurements with genetic data to reach a clear conclusion.

DNA barcoding confirmed new species

DNA barcoding is a method, widely adopted since 2003, that uses short DNA sequences to identify species with consistency across labs and continents. It supports, rather than replaces, traditional anatomy by adding a measurable genetic line.

In this study, the scientists looked at a piece of DNA that codes for the protein cytochrome b, along with other parts of the animal’s DNA. They then compared these genetic pieces to samples kept in museum collections.

The results showed that the animal from Peru is related to Marmosa lepida and Marmosa andersoni, but is clearly a different species.

“The animal from Abiseo is very different in its DNA, about 8% different from Marmosa lepida,” wrote Pavan. For small mammals, that much difference is considered a big gap and shows that this species has been separate for a long time.

What sets Marmosa chachapoya apart

Species status does not rest on DNA alone. The researchers documented a long, narrow face and a tail that is longer than the head and body combined, which is typical for these agile climbers.

The animal also had “a remarkably narrow and long rostrum with a very long premaxillary process; absence of postorbital processes,” wrote Pavan.

The belly fur is orange with a gray base, and the facial mask is dark but does not stretch back to the ears.

Andes keep turning up surprises

The eastern Andes is home to many species that only exist in small, separate areas, a pattern known as endemism.

Scientists consider this region one of the richest biodiversity zones in South America. Many species of animals occur here that are both unique and threatened.

The discovery of Marmosa chachapoya also revises the altitudinal limits of its group. While its close relatives have only been found as high as about 5,187 feet (1,580 meters), this new species was recorded at 8,740 feet (2,660 meters) in the cloud forests of Río Abiseo.

Cloud forest bands change quickly with height, and species often swap out along the slope. That patchwork helps explain why short field windows can still turn up animals that science has not yet named.

Río Abiseo is not just scenic. It is a protected landscape with archaeological sites and intact ecological processes that allow small mammals to persist in pockets that are hard to reach.

The Park’s legal status limits access, so surveys depend on careful planning and permits. That makes each specimen count, especially when populations are small or scattered.

One Marmosa specimen gives solid evidence

Describing a species from a single specimen can sound thin. In this case, the authors backed the designation with multiple lines of evidence, from cranial features to DNA from four genes.

They also anchored the comparisons in museum collections across the Americas.

The researchers noted traits that might vary with age, such as glands and skull ridges.

They also explained why those would not erase the clear differences they had documented. It is a cautious approach that invites follow-up while making the data usable now.

Why Marmosa chachapoya matters

Every time a species is named and positioned on the tree of life, it becomes easier to track, protect, and study.

Laws, park plans, and conservation funding work better when the organisms have names and documented ranges.

There is also a local story here. The species epithet honors people of the Chachapoya culture, whose legacy is part of the same landscape that shelters this animal today.

Future trips will aim to find more of these animals and figure out exactly where they live between the Marañón and Huallaga rivers.

Teams will search at the same heights and in similar forests to learn if the species is limited to one small area or spread across more of the cloud forests.

New DNA studies could help show how it fits in with its closest relatives. Collecting more animals will also reveal details about its size, behavior, and how much it varies in different places.

The study is published in American Museum Novitates.

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