Metachirus myosuros ( Temminck, 1824 )

Voss, Robert S., Fleck, David W. & Jansa, Sharon A., 2019, Mammalian Diversity And Matses Ethnomammalogy In Amazonian Peru Part 3: Marsupials (Didelphimorphia), Bulletin of the American Museum of Natural History 2019 (432), pp. 1-89 : 41-46

Metachirus myosuros ( Temminck, 1824)

Figures 13B , 14B , 15B

VOUCHER MATERIAL (TOTAL = 12): Nuevo San Juan (AMNH 268217, 268218, 272780, 273057; MUSM 11049, 11051, 11053, 11054, 13293, 15308, 15309), San Fernando (FMNH 89001).

OTHER INTERFLUVIAL RECORDS: Jenaro Herrera (as Metachirus nudicaudatus ; Pacheco, 1991; Pavlinov, 1994; Fleck and Harder, 1995), San Pedro (as M. nudicaudatus ; Valqui, 1999, 2001).

IDENTIFICATION: Same-sex morphometric comparisons of our voucher material and other specimens from southwestern Amazonia with typical examples of Metachirus nudicaudatus (from northeastern Amazonia) document broad overlap in most external and craniodental dimensions (table 14). However, side-by-side visual comparisons of skulls reveal consistent differences in other aspects of craniodental morphology (table 15). Most conspicuously, the left and right scars that mark the dorsalmost origin of the temporalis muscle on each side of the skull are only weakly convergent posteriorly in most specimens of typical M. nudicaudatus , usually remaining widely separated over the parietals and interparietal (fig. 13A); if a sagittal crest is formed, usually in large adult male specimens, it is restricted to the midline of the interparietal. By contrast, the temporalis scars are more strongly convergent posteriorly in fully adult specimens from southwestern Amazonia, often uniting on the midline of the posterior braincase to form a low sagittal crest over the interparietal and along the mid-parietal suture (fig. 13B). Additionally, the rostrum tends to be more robust and the zygomatic arches tend to be more rounded laterally in southwestern Amazonian material than in M. nudicaudatus , which typically has a longer, narrower rostrum

TABLE 14

and almost parallel-sided zygomatic arches. In ventral view, the maxillopalatine fenestrae are much shorter and narrower in southwestern Amazonian specimens than in typical M. nudicaudatus (fig. 14), and statistical comparisons of fenestral length and width confirm that these visually obvious differences are highly significant (p <0.0001 by two-tailed Student’s t tests). Although subtle differences in the dentition also appear to distinguish southwest- ern Amazonian specimens from typical M. nudicaudatus , the only dental character that we were able to score with confidence was size of the entoconid. This is a small cusp, subequal to or sometimes smaller than the paraconid on unworn m1–m 3 in M. nudicaudatus (fig. 15A), but it is a large cusp, substantially bulkier than the paraconid and almost equal in size to the hypoconid in southwestern Amazonian specimens (fig. 15B).

TABLE 15

To supplement our morphological comparisons, we sequenced the entire mitochondrial gene encoding cytochrome b from ethanolpreserved tissues of 29 specimens of Metachirus from 27 localities in Central and South America representing most of the nominal taxa currently treated as synonyms or subspecies of Metachirus nudicaudatus (fig. 16, appendix 4). The best-fitting topology obtained from maximum-likelihood analysis of this dataset (fig. 17) recovered a strongly supported basal dichotomy between sequences from northeastern Amazonia ( French Guiana, Guyana, and Surinam) and those from elsewhere in the geographic range of the genus; uncorrected pairwise distances across this basal split are about 11.2%, on average, and are much larger than any others we obtained from these data (table 16). The mtDNA haplogroup that includes our sequenced vouchers (“SW Amazonia”) also includes sequences from southern Peru (Cuzco and Madre de Dios), eastern Bolivia (Cochabamba and La Paz), and western Brazil (Acre and Amazonas). Uncorrected pairwise distances within this group are uniformly small (about 1.4% on average), and visual inspection of the gene tree suggests that there is little (if any) internal phylogeographic structure. Sister to this clade is a group of sequences from the Atlantic Forest of southeastern Brazil, and these two haplogroups are sister to a clade that includes sequences from northwestern Amazonia and Central America.

Although a comprehensive revision of Metachirus is beyond the scope of this report, the results described in the preceding paragraphs clearly suggest that our southwestern Amazonian material is specifically distinct from M. nudicaudatus which, based on specimens we personally examined (see below), seems to be endemic to northeastern Amazonia ( French Guiana, Guyana, Surinam, and the Brazilian state of Amapá). Of the many nominal taxa currently referred to the genus (table 17), the oldest that applies to our material is M. myosuros , which is based on a lectotype from southeastern Brazil. Specimens that we examined from southeastern Brazil (mostly from Rio de Janeiro and São Paulo at the AMNH, FMNH, and USNM; not listed below) closely

TABLE 16

resemble our material from southwestern Amazonia in all the traits previously discussed, which we regard as diagnostic of the species. Because types and other material of the remaining nominal taxa currently referred to Metachirus more closely resemble M. myosuros than M. nudicaudatus , we provisionally treat them as junior synonyms of the former species; all are based on seemingly minor coat-color differences, and none appears to exhibit morphometric traits that exceed the range of variation in our southwestern Amazonian series.

The absence of any sequence data from southeastern Amazonia (south of the Amazon and east of the Rio Madeira) is a major hiatus in our genetic sampling, so only phenotypic traits are available for identification of the populations that occur there. Specimens from localities on the right (east) bank of the Tocantins (e.g., Baião, Belém, Bragança, and Capim; at the AMNH and USNM) exhibit all the diagnostic craniodental traits of Metachirus myosuros , whereas those from the Tocantins-Xingu interfluve are morphologically distinctive (e.g., with large maxillopalatine fenestrae and small entoconids like M. nudicaudatus , but with strongly convergent temporalis scars like M. myosuros ). Patton et al. (2000) reported a highly divergent cytochrome b sequence from this region, but we have not seen the voucher specimen (in Manaus), nor was this sequence included in a subsequent analyses of Metachirus mitochondrial DNA ( Costa and Patton, 2006). Additional sequence data from this region would be very welcome, as would a careful assessment of associated morphological material.

ETHNOBIOLOGY: The Matses do not distinguish this species from other “four-eyed” opossums (all known as cheka bëbëdi; see the account for Philander , below) and therefore have no particular beliefs about it.

MATSES NATURAL HISTORY: The Matses have no definite knowledge of this species.

REMARKS: Of the 11 specimens of Metachirus myosuros for which we have capture information, seven were trapped on the ground or near ground level (one was trapped on a fallen log), two were shot on the ground at night, one was caught by hand in the daytime as it ran out of a leaf nest on the ground, and another was caught by hand on the ground in the late afternoon as it was eating fallen guavas. One trapped specimen is also known to have been captured in the daytime (between 06:30 and 15:00 hours). Four of these specimens were taken in primary upland forest, whereas seven were in secondary growth (abandoned swiddens).

OTHER SPECIMENS EXAMINED FROM SW AMA- ZONIA (TOTAL = 39): Bolivia — Cochabamba, Cavernas de Repechón (MSB 70283); La Paz, Chulumani (BMNH 1.6.7.69–1.6.7.74 [type series of bolivianus]). Brazil — Acre, Nova Vida on right bank Rio Juruá (MVZ 190296, 190297), Sena Madureira (USNM 546190, 546191); Amazonas, Condor on left bank Rio Juruá (MVZ 190288), Penedo on right bank Rio Juruá (MVZ 190287), Vira Volta on left bank Rio Juruá (MVZ 190299); Rondônia, 8 km N Porto Velho (USNM 390034, 390035). Peru — Cuzco, Consuelo (FMNH 174437, 174441), Huajyumbe (FMNH 84248), Kiteni on Río Urubamba (MVZ 166505), Quincemil (FMNH 75097, 75098); Junín, Chanchamayo (FMNH 18206), San Ramón (FMNH 20795, 20798); Loreto, Santa Elena on Río Samiria (FMNH 87128); Madre de Dios, Hacienda Érica (MVZ 166501, 166504), “Inambari River” (BMNH 2.7.27.8 [holotype of infuscus]), Lago Sandoval (MVZ 157634), Puerto Maldonado (USNM 390040), 4 km S Puerto Maldonado (USNM 390036), 4 km W Puerto Maldo- nado (USNM 390039), 2.75 km E Shintuya (FMNH 169803); Pasco, Pozuzo (FMNH 24788), San Juan (USNM 364161); Ucayali, Balta (MVZ 136383, 136384), 59 km SW Pucallpa (USNM 499009).

SPECIMENS OF METACHIRUS NUDICAUDATUS EXAMINED (TOTAL = 33): Brazil — Amap á, Serra do Navio (USNM 393544–393553, 461456, 461457, 545544, 546189). French Guiana— Paracou (AMNH 266435, 266440, 266449, 266450, 266455, 267009, 267010; MNHN 1995.906, 1995.907), “River Arataye” (USNM 548440). Guyana — East Berbice-Corentyne, Amuku Creek (ROM 34252); Potaro-Siparuni, Iwokrama Forest (ROM 111938); Rupununi, 30 mi E Dadanawa (ROM 32459), Kwitaro River (ROM 33051). Surinam — Brokopondo, Brownsberg Nature Park (ROM 114155); Sipaliwini, Bakhuis Transect 9 (ROM 117030), Bakhuis Transect 11 (ROM 117525), Iconja Landing (ROM 120317), Tafelberg (ROM 119571).

Figures

FIG. 13. Dorsal cranial views of A, Metachirus nudicaudatus (AMNH 267009, an adult male from French Guiana) and B, M. myosuros (AMNH 273057, an adult male from the Yavarí-Ucayali interfluve).

FIG. 14. Ventral views of palates of A, Metachirus nudicaudatus (AMNH 266449) and B, M. myosuros (MUSM 15309) illustrating species divergence in size of the maxillopalatine fenestrae (mpf).

FIG. 15. Lingual views of lower molars of A, M. nudicaudatus (AMNH 266451) and B, M. myosuros (AMNH 268218) illustrating species divergence in relative size of the entoconid (en) and paraconid (pa).