New record of Marmosa ( Stegomarmosa ) andersoni Pine , 1972 ( Didelphimorphia , Didelphidae ) , a rare and endemic Peruvian marsupial

Marmosa (Stegomarmosa) andersoni Pine, 1972 is one of the rarest members of the genus Marmosa. This species is endemic to southeastern Peru and currently known from only 3 close localities in Cusco. Herein we report a new record for the species from Pasco, which extends its geographic distribution by 360 km and represents its northernmost record.


Introduction
The genus Marmosa Gray, 1821, includes a diverse group of species of South American marsupials which contain 19 recognized species (Voss et al. 2014).However, several of them appear to be species complexes (Tate 1933, Anderson 1997, Patton et al. 2000, Patton and Costa 2003, Creighton and Gardner 2007).At present, based on molecular evidence, 5 subgenera are recognized (Voss et al. 2014).One of them, Stegomarmosa Pine 1972, contains 2 species, Marmosa lepida (Thomas, 1888) and M. andersoni Pine, 1972(Voss et al. 2014).Since its discovery, M. (Stegomarmosa) andersoni drew attention for the great development of its postorbital processes, similar to those presented by Caluromys (Reig et al. 1987), for its narrow interorbital constriction, and for the unique arrangement of tail hairs (Pine 1972), which earned its assignment to a subgenus of its own.Among Marmosa species, M. andersoni is one of the rarest species with just 3 close localities reported, and only known by 7 specimens (Solari and Pine 2008).In fact, its conservation status is considered as Data Deficient by IUCN Red List, in view of insufficient knowledge of its ecology and distribution (Solari 2015).

Methods
The new specimen of M. andersoni was collected by one of the authors (HC), a park-ranger of Yanachaga Chemillén National Park, who found the specimen lying dead on a trail near the Huampal Control Station.The specimen, an adult male, was catalogued in the Scientific Collection associated with the Museo de Historia Natural of the Universidad Nacional de San Agustín with the catalog number MUSA 6542, preserved in alcohol and with its skull removed (Fig. 2).
External and cranial measurements of the specimen were taken following Solari and Pine (2008), Pine (1972), Patton et al. (2000) and Voss et al. (2001): Total length (TL), tail length (LT), hind paw length (HF), ear length (E) and weight (W) in grams, head and body length (HBL) was obtained by subtracting LT from TL.
Identification.The specimen exhibits the following combination of diagnostic characters described by Pine (1972), and Solari and Pine (2008): postorbital processes exceptionally developed, measuring 10.1 mm between their ends and protruding 2.8 mm from their base, forming a triangular flange or shield (Fig. 2); strongly constricted interorbital area; exceptionally large orbits; ascending ramus of the dentary forming an unusually obtuse angle with the horizontal body of the dentary; lower canine procumbent and apically laterally flattened.In our specimen, however, the first lower premolars are not in broad contact with the lower canines (Fig. 2), as reported for most specimens of this taxon.Some variation regarding the contact between the first lower premolar and the lower canine has been previously reported (Solari and Pine 2008), and the present record indicates a greater variation in this character than previously known for the species.Palatal fenestrations are partially perforated, with the right side of the palate fenestrated from the middle of M1 to M2, and the right side from the middle of P3 to the posterior border of M2 (Fig. 2).A throat gland is present, as well as the tail dorsally almost naked but with the presence of bristles ventrally on either side (Fig. 3B).These bristles are brown and short in the basal part of the tail and form a welldeveloped fringe of long silvery bristles distally (Fig. 3C,  D).Pattern of scales of tail ranging from annular to spiral (Fig. 3E).Moreover, the specimen from Pasco (MUSA 6542) exhibits slight differences (less than 1 mm) in some cranial measurements (condyle basal length, minor interorbital, zygomatic breadth, palatal length, palatal width, upper molar toothrow, maximum width between third molars; see Table 1) that could be considered as intraspecific variation.

Discussion
The geographic distribution of M. andersoni expands 360 km to the northwest and its upper elevational limit up to 1100 m a.s.l.This update of its distribution suggests that M. andersoni inhabits several forest types, such as lowland tropical rainforest (previous records, Solari and Pine 2008) and montane pluvial forest of the Yungas (following Olson et al. 2001, this record).

Figure 2 .
Figure 2. Dorsal and ventral views of the cranium and lateral view of the cranium and mandible of an adult male of Marmosa (Stegomarmosa) andersoni (MUSA 6542), collected in the Quebrada Honda, Huampal, Pasco, Peru.Scale bar = 10 mm.
endemic fauna and flora, depicting one of the major centers of endemism around the world(Young 2007, Patterson et al. 2012), awakening the interest of researchers for several years, to understand the origin of this pattern and the biogeographic history of the species that inhabit this region and the related lowlands species(Hershkovitz 1972, Patton and Smith 1992, Bates and Zink 1994, Fjeldså and Rahbek 2006, Brumfield and Edwards 2006, Hughes and Eastwood 2006, Patterson and Velazco 2008, Patterson et al. 2012).

Figure 3 .
Figure 3. Lateral view of the skin of Marmosa (Stegodermosa) andersoni (MUSA 6542).B. Lateral view of the distal portion of tail showing a well-developed fringe of silvery bristles.C, D. Ventral view of the basal and distal portions of tail point out the variation of the color and size of the bristles and the mid-ventral naked pattern (see text for detail description).E. Dorsal view of tail illustrating the pattern of scales ranging from annular (inside white square) to spiral.