Marmosops juninensis ( Tate, 1931 )

Díaz-Nieto, Juan F. & Voss, Robert S., 2016, A Revision Of The Didelphid Marsupial Genus Marmosops, Part 1. Species Of The Subgenus Sciophanes, Bulletin of the American Museum of Natural History 2016 (402), pp. 1-72 : 49-52

Marmosops juninensis ( Tate, 1931)

Figures 5B , 21 , 22 , 23B

Marmosa juninensis Tate, 1931: 13 (original description).

Marmosa parvidens juninensis: Pine, 1981: 64 (name combination).

Marmosops parvidens juninensis: Gardner, 1993: 20 (name combination).

Marmosops juninensis: Emmons, 1990: 22 (first use of current binomial).

TYPE MATERIAL: The holotype (by original designation) consists of the skin and skull of a young adult female ( AMNH 63864) collected by

H. Watkins on 25 February 1929 at Utcuyacu (fig. 24: locality 68), between Tarma and Chanchamayo, in Junín department, Peru, at an altitude of 4800 feet (1463 m).

DISTRIBUTION, HABITATS, AND SYMPATRY: Examined specimens suggest that Marmosops juninensis has a restricted distribution in premontane and montane rain forest on the eastern slopes of the Peruvian Andes in the departments of Junín and Pasco between 1387 and 2316 m above sea level. According to Peralta and Pacheco (2014), at the lower limit of its elevational range M. juninensis occurs sympatrically with M. bishopi , where at least two species of the nominotypical subgenus ( M. noctivagus and a member of the M. caucae complex) could also be expected to occur.

DESCRIPTION: Body pelage reddish brown (near Prout’s Brown) middorsally, indistinctly paler laterally, and about 7–9 mm long at midback; ventral pelage superficially whitish, but hairs extensively gray based on throat, chest, and abdomen (including the insides of the fore- and hind limbs), with or without a narrow, discontinuous midventral streak of self-white fur. 12 Manus covered dorsally with uniformly pale hairs (the metacarpals not contrasting sharply in color with the digits); lateral carpal tubercles bladelike. Mam-

12 Voss et al. (2001: 48) described the ventral fur as “entirely gray-based,” corresponding to the phenotype seen in AMNH specimens, but Peralta and Pacheco (2014) described and illustrated recently collected material with a midventral streak of self-white fur.

mary formula unknown (no female specimens with visible teats were examined). Tail substantially longer than combined length of head and body (mean LT/HBL × 100 = 126%–137%); dorsal caudal surface dark (perhaps brownish in life), ventral surface indistinctly paler.

Nasals long (extending well behind the lacrimals) and much wider posteriorly than anteriorly (laterally expanded at the maxillary-frontal suture). Lacrimal foramina concealed from lateral view inside anterior orbital margin; apex of zygomatic process of squamosal distinctively rounded anteriorly and not (or only slightly) overlapped dorsally by jugal. Palatine fenestrae consistently present, but sometimes irregular in size and shape. Dorsolateral margin of ethmoid foramen formed by the frontal.

Upper canine (C1) with only posterior accessory cusp in both sexes. Upper third molar (M3) anterolabial cingulum narrowly continuous with preprotocrista (anterior cingulum complete). Lower canine (c1) premolariform (with posterior accessory cusp) and small, subequal in height to p1; c1 anterolingual accessory cusp usually present but very small. First lower molar (m1) entoconid shorter than m2 paraconid; unworn m4 talonid with three distinct cusps.

COMPARISONS: Comparisons of Marmosops juninensis with M. bishopi are provided in the preceding account.

Marmosops juninensis seems to be about the same size as M. ojastii (table 8), but with the small samples available for both species, morphometric inference is problematic. In side-byside comparisons of skins these species are most readily distinguished by ventral pelage coloration: whereas the ventral pelage of M. juninensis is extensively gray based (with only a discontinuous midventral streak of self-white fur), the ventral pelage of M. ojastii is almost entirely self-white with no trace of gray-based hairs. Marmosops juninensis can also be unambiguously distinguished from M. ojastii by several craniodental characters including dorsal overlap between the squamosal and jugal (shallow or absent in M. juninensis versus extensive in M. ojastii ), the dorsolateral margin of the ethmoid foramen (usually formed by the frontal in M. juninensis versus by the orbitosphenoid in M. ojastii ), palatine fenestrae (consistently present in M. juninensis versus absent in M. ojastii ), and a lingual accessory cusp on c1 (present in M. juninensis but absent in M. ojastii ).

Insofar as can be judged from our small samples, Marmosops juninensis and M. chucha are about the same size. Skins of these species are distinguishable by ventral pelage coloration, which is extensively gray based in M. juninensis (notably on the throat and inside surfaces of the fore- and hind limbs) but broadly self-white in M. chucha (in which the throat is always selfwhite and the inside surfaces of the limbs usually have some self-white markings). In qualitative cranial comparisons, these species can be readily distinguished based on squamosal-jugal overlap (the jugal only slightly overlaps the zygomatic process of the squamosal in M. juninensis , whereas dorsal overlap between the jugal and squamosal bone is extensive in M. chucha ), palatine fenestration (palatine fenestrae are consis- tently present and large in M. juninensis whereas palatine fenestrae are minute or absent in M. chucha ), and the lingual accessory cusp of c1 (usually present in M. juninensis versus usually absent in M. chucha ).

Marmosops juninensis is likewise similar in size to M. magdalenae , from which it cannot confidently be distinguished based on measurement data alone. However, these species are distinguishable by ventral pelage coloration (extensively gray based in M. juninensis versus extensively self-white in M. magdalenae ), dorsal overlap between the jugal and squamosal zygomatic process (shallow or absent in M. juninensis versus extensive in M. magdalenae ), the lingual accessory cusp on c1 (usually present in M. juninensis versus usually absent in M. magdalenae ), and the number of m4 talonid cusps (three in M. juninensis versus two in M. magdalenae ).

REMARKS: The Pasco specimen (LSU 25902) is a juvenile male, but it is a good match in pelage and dental traits with other material referred to this species. In particular, the ventral fur of LSU 25902 is entirely gray based, C1 has a distinct posterior accessory cusp, and the combined length of M1–M2 is 3.5 mm (versus 3.4–3.6 mm in AMNH specimens, including the holotype).

SPECIMENS EXAMINED (N = 7): Peru— Junín, San Antonio (MUSM 40616, 40617), 22 mi E Tarma (AMNH 230014–230016), Utcuyacu (AMNH 63864); Pasco, Santa Cruz (LSU 25902).

Figures

FIG. 5. Ventral views of the palates of Marmosops parvidens (A, AMNH 267359), M. juninensis (B, AMNH 230016), and M. magdalenae (C, ICN 19926) illustrating species differences in the presence, absence, and morphology of palatal fenestrae and foramina. Abbreviations: if, incisive foramen; max, maxillary bone; mp, maxillopalatine fenestra; p, palatine fenestrae; pal, palatine bone; plpf, posterolateral palatine foramen; pre, premaxillary bone.

FIG. 21. Dorsal and ventral views of skulls of Marmosops bishopi (left, MUSM 23803) and M. juninensis (right, AMNH 230016). All views about ×3.

FIG. 22. Lateral views of skulls and mandibles of Marmosops bishopi (above, MUSM 23803) and M. juninensis (below, AMNH 230016). All views about ×3.

FIG. 23. Lateral view of zygomatic arch of Marmosops bishopi (A, MUSM 23803) and M. juninensis (B, AMNH 230016) illustrating species differences in the extent of dorsal overlap between the zygomatic process of the squamosal (zps) and the jugal (jug).