Philander nigratus ( Thomas, 1923 )

Voss, Robert S. & Giarla, Thomas C., 2020, A Revision of Philander (Marsupialia: Didelphidae), Part 2: Phylogenetic Relationships and Morphological Diagnosis of P. nigratus Thomas, 1923, American Museum Novitates 2020 (3955), pp. 1-16 : 7-12

Philander nigratus ( Thomas, 1923)

Metachirus opossum nigratus Thomas, 1923: 603 ; type locality “Utcuyaco” (= Utcuyacu, ca. 11°12′ S, 75°28′ W; Stephens and Traylor, 1983) at 1600 m above sea level in Junín department, Peru .

Metachirops opossum nigratus: Krumbiegel, 1941: 202 ; name combination.

Philander opossum canus: Cabrera, 1958: 35 ; part ( nigratus treated as a synonym), not P. canus (Osgood, 1913) .

Philander andersoni: Gardner, 1993: 22 ; part ( nigratus treated as a synonym), not P. andersoni

(Osgood, 1913).

Philander andersoni andersoni: Hershkovitz, 1997: 61 ; part ( nigratus treated as a synonym), not P. andersoni (Osgood, 1913) .

TYPE MATERIAL: The holotype (by original designation, BMNH 0.7.7.62) consists of the skin and skull of an old adult female ( figs. 3 , 4 ) collected at Utcuyacu by P.O. Simons (original number 947) on 21 April 1900. Two other specimens mentioned by Thomas (1923) are paratypes; both were collected by Jean Kalinowski at “Chanchamayo” and were obtained by the BMNH in 1894 from the Branicki Museum in Warsaw. 3 One paratype ( BMNH 94.10.1.16) consists of the skin of a young (possibly subadult) individual of unknown sex without an accompanying skull, whereas the other ( BMNH 94.10.1.17) is the skull of an old adult of unknown sex without an accompanying skin .

DISTRIBUTION AND SYMPATRY: Philander nigratus is known only from the eastern Andean foothills at recorded elevations of 1000–1600 m in the Peruvian departments of Ayacucho and Junín. It is not known to occur sympatrically with other congeneric species .

MORPHOLOGICAL CHARACTERS: Dorsal pelage short (not shaggy), about 12–17 mm long middorsally (mean = 15 mm) and more or less uniformly dark gray (sometimes indistinctly darker middorsally but never with a distinct middorsal stripe); fur of crown (between the ears) clear blackish in some specimens (e.g., BMNH 0.7.7.62, LSUMZ 16398) but grizzled gray in others (e.g., MUSM 71, FMNH 65782); pale preauricular spot absent in most specimens but indistinct in one (FMNH 65782); ventral fur frosted dark gray (the individual hairs grayish basally, 3 Although Chanchamayo is the name of a province in northern Junín department, its use by 19th-century collectors is generally understood to refer to the valley of the Río Chanchamayo, a tributary of the Río Perené. According to Berlepsch and Stolzmann (1896), Kalinowski collected at three localities in the valley of the Chanchamayo: La Merced (11°03′S, 75°19′W, ca. 800 m; Stephens and Traylor, 1983), La Gloria (coordinates unknown; ca. 975 m), and Borgoña (ca. 11°05′S, 75°20′W, ca. 795 m; Stephens and Traylor, 1983). None of these localities, however, is indicated on the labels that accompany the specimens in question.

but with paler tips); scaly part of tail ≤¼ white (unpigmented) distally. Nasal bones long, extending between postorbital processes in some specimens (e.g., BMNH 0.7.7.62, 28.5.1.20), but much shorter in others (MUSM 71, LSUMZ 16399); posterior margin of nasals laterally notched in some specimens (e.g., BMNH 0.7.7.62) or without posterolateral notches (LSUMZ 16398). Third upper premolar (P3) labial cingulum incomplete in most specimens but complete in one (LSUMZ 16399); crown length of upper molar series 14.7–16.4 mm (N = 5).

COMPARISONS: Philander nigratus requires close comparison with two other western-Amazonian species of the Opossum Group— P. andersoni and P. mcilhennyi —which it somewhat resembles in size and coloration ( Gardner and Patton, 1972; Patton and da Silva, 1997). Additionally, P.nigratus merits comparison to P.canus , a taxon with which it was once synonymized, and with which it might reasonably be expected to occur sympatrically. Wider comparisons (e.g., with eastern Amazonian, trans-Andean, or Atlantic Forest taxa) seem unnecessary in the absence of compelling molecular support for close relationships to other species.

Philander nigratus differs externally from P. andersoni by lacking the distinct blackish middorsal stripe that is invariably present in the latter species (illustrated by Voss et al., 2018: fig. 10). Additionally, the pale preauricular spots that are consistently present in P. andersoni are absent or indistinct in P. nigratus , and the scaly part of the tail, which is ½ to ⅔ white in P. andersoni is ¼ white in P. nigratus . The two species are craniodentally similar in qualitative features, but P3 usually has a complete labial cingulum in P. andersoni , whereas P3 has an incomplete labial cingulum in six of the seven specimens of P. nigratus that we were able to score for this trait. Morphometrically, however, P.nigratus is substantially larger than P. andersoni , a size difference that is most noticeable in molar measurements, some of which have almost nonoverlapping observed ranges for these species ( table 3 ).

Philander nigratus differs in dorsal pelage color from P. mcilhennyi , which is either darker overall in dorsal pelage color (almost completely blackish) or has a distinct blackish middorsal stripe and pale-grayish flanks ( Voss et al., 2019: fig. 19). Although the two species overlap broadly in dorsal pelage length, this is at least partly due to sexual dimorphism in P. mcilhennyi (females having longer, shaggier middorsal fur than males; Voss et al., 2019); the single dorsalpelage length measurement we obtained for an adult female P.nigratus was just 16 mm, whereas some adult females of P. mcilhennyi have middorsal fur that is 19–21 mm long. The most conspicuous and consistent external difference, however, is tail coloration: whereas the scaly part of the tail is usually ½ to ⅔ whitish distally in P. mcilhennyi , no more than ¼ of the tail is whitish distally in P. nigratus . These two species are craniodentally similar, and they have broadly overlapping measurements, but P3 has a complete labial cingulum in P. mcilhennyi , whereas the labial cingulum of P3 is usually incomplete in P. nigratus .

Philander canus (redescribed and illustrated by Voss et al., 2018) differs from P. nigratus by its pale-gray dorsal pelage, self-whitish ventral pelage, and longer white tail tip. Philander canus is also a substantially smaller animal than P. nigratus (e.g., with nonoverlapping molar toothrow measurements: 12.2–13.7 mm versus 14.7–16.4 mm). Additionally, the nasal bones are consistently short in P. canus (never extending posteriorly to or between the postorbital

processes) and the labial cingulum of P3 is always complete, whereas the nasal bones are longer in about half the examined specimens of P.nigratus , which usually also has an incomplete labial cingulum on P3.

SPECIMENS EXAMINED (N = 8): Peru — Ayacucho, Huanhuachayo (LSUMZ 16399), San José (LSUMZ 16398); Junín, Chanchamayo (BMNH 94.10.1.16, 94.10.1.17; FMNH 65782), Ináñez (BMNH 28.5.1.21), Peñablanca (MUSM 71), Utcuyacu (BMNH 0.7.7.62).

Figures

FIG. 3. Dorsal and ventral views of the holotype skin (BMNH 0.7.7.62) of Philander nigratus.

FIG. 4. Dorsal and ventral views of the holotype skull (BMNH 0.7.7.62) of Philander nigratus.