Marmosa chachapoya

（Courtesy of Pedro Peloso ）

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Taxonomy

Kingdom: Animalia

Phylum: Chordata

Class: Mammalia

Order: Didelphimorphia

Family: Didelphidae

Genus: Marmosa

Species: Marmosa chachapoya

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Morphological Description

The Chachapoya mouse opossum (Marmosa chachapoya) is a small to medium-sized species within the genus Marmosa. The combined length of the head and body is approximately 10.7 cm. The skull is overall slender with a markedly elongated and narrow rostrum. Postorbital processes are absent, a feature that is unusual among other species in the same subgenus. The interorbital region is relatively broad and does not appear strongly constricted when compared with the width of the zygomatic arches. The cranial roof lacks both a sagittal crest and an occipital crest, and temporal ridges are indistinct. The zygomatic arches reach their greatest width anterior to the orbits.

In terms of pelage, the dorsal fur is generally reddish brown, with the flanks slightly paler than the mid-dorsal region. The basal portion of most dorsal hairs is gray, whereas the tips range from buffy to dark brown. The ventral pelage is buffy-reddish overall; the bases of the ventral hairs are gray rather than pure white, and only the chin and scrotal fur are cream-colored. A continuous white midventral stripe is absent. The pinnae appear almost naked but are covered internally and externally with short pale-yellow hairs.

The limbs are covered with dense pale-yellow fur. The claws of the hands are short and do not extend beyond the fleshy digital pads. A lateral carpal tubercle is present at the wrist. The tail is much longer than the head-and-body length, reaching about 16 cm, and is strongly prehensile. The ventral prehensile surface bears dense fringes of long hairs. Caudal scales are arranged primarily in spiral series, and the tail coloration is uniformly brown.

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Etymology

The genus name Marmosa refers to mouse opossums.

The species name chachapoya refers to the Chachapoyas, an indigenous culture that historically inhabited the cloud forests of the eastern Andes in northern Peru. The term likely derives from Quechua and is commonly interpreted as meaning “cloud forest,” reflecting the high-elevation cloud-forest habitat where this species is currently known to occur.

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Biological Description

At present, the Chachapoya mouse opossum is known only from the eastern side of Parque Nacional del Río Abiseo in the San Martín Department of Peru, at an elevation of approximately 2,664 meters. The holotype is a young adult male captured in a pitfall trapline within dense forest. The habitat corresponds to upper montane rainforest, characterized by a canopy approximately 20–30 meters tall, dense understory vegetation, and abundant epiphytes such as mosses, ferns, lichens, orchids, and bromeliads.

Several other small mammals were captured at the same site, including species of Akodon, Nephelomys, Thomasomys, and other marsupials, indicating that the area harbors exceptionally high mammalian diversity. Based on the currently available single specimen, the species is likely a specialist of high-elevation cloud forests and is unlikely to extend into the Amazonian lowlands. Compared with other members of the same subgenus, its distribution occurs at a considerably higher elevation, suggesting evolutionary adaptation to the cool, humid, and structurally complex environment of montane forests.

Molecular analyses further support its distinctiveness. Both mitochondrial and nuclear DNA sequences show clear divergence from closely related species such as Marmosa lepida and Marmosa andersoni, forming a well-supported independent evolutionary lineage. Although the current sample size is insufficient to completely rule out age-related morphological variation, several cranial, dental, and pelage characteristics fall outside the known range of ontogenetic variation, indicating that these traits reliably diagnose a distinct species.

（Author: Shui-Ye You）

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Reference

Pavan SE et al. (2025). A New Species of Marmosa (Mammalia: Didelphimorphia: Didelphidae) from Parque Nacional del Río Abiseo, Peru. American Museum Novitates.

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