Marmosa (Exulomarmosa) isthmica Goldman, 1912

Voss, Robert S., 2022, An Annotated Checklist Of Recent Opossums (Mammalia: Didelphidae), Bulletin of the American Museum of Natural History 2022 (455), pp. 1-77 : 11

Marmosa (Exulomarmosa) isthmica Goldman, 1912

TYPE MATERIAL AND TYPE LOCALITY: USNM 170969 , the holotype by original designation, consists of the skin and skull of an adult male collected on the Río Indio (9.25° N, 79.98° W; at sea level), a tributary of the lower Río Chagres near Gatún, Colón province, Panama .

SYNONYMS: mimetra Thomas, 1921; regina Thomas, 1898 (suppressed; see Remarks).

DISTRIBUTION: Marmosa isthmica is known from humid lowland and lower-montane localities (usually below 1700 m) in Panama, western Colombia (including the interAndean Cauca and Magdalena valleys), and western Ecuador ( Rossi et al., 2010: fig. 22).

REMARKS: Originally described as a full species, Marmosa isthmica was treated for many years as a subspecies or synonym of M. robinsoni (after Hershkovitz, 1951). Current usage follows Rossi et al. (2010), who demonstrated that M. isthmica and M. robinsoni are morphologically distinct, known to occur in sympatry, and usually occupy different habitats ( M. isthmica in rainforest, M. robinsoni in dry forest). A subsequent mtDNA sequencing study ( Gutiérrez et al., 2010) provided compelling evidence that these are, in fact, genetically distinct species.

Although Marmosa regina is a senior synonym of M. isthmica , the former name has long been misapplied to species in the subgenus Micoureus . To preserve long-standing binomial usage of M. isthmica, Voss and Giarla (2020a) petitioned the International Commission on Zoological Nomenclature to suppress usage of M. regina . A ruling from the Commission is pending.