AMERICAN MUSEUM NOVITATES 
ABSTRACT 
In order to facilitate much-needed revisionary research on Marmosops, we summarize the 
currently accepted species-level taxonomy, provide full bibliographic citations for original 
descriptions of all 36 included nominal taxa, map their type localities, and list their type 
material (if known). We rediagnose the genus Marmosops, compare it with three other didel- 
phid genera to which misidentified specimens of Marmosops have often been referred, and 
review the phylogenetic evidence that Marmosops is monophyletic. After describing a new 
species from the eastern-slope montane forests of Bolivia, we review the taxonomy of other 
Bolivian congeners based on morphological characters and published cytochrome-b gene se- 
quences. Among our taxonomic results, we synonymize albiventris Tate (1931), dorothea 
Thomas (1911), and yungasensis Tate (1931) with M. noctivagus (Tschudi, 1845). By contrast, 
M. ocellatus (Tate, 1931), currently considered a synonym of dorothea, appears to be a valid 
species. Whereas published range maps of Bolivian species of Marmosops are demonstrably 
based on misidentified material and show little correspondence with known environmental 
factors, locality records based on specimens examined for this report make much more eco- 
NO. 3466 
geographic sense. 
INTRODUCTION 
Didelphid marsupials represent the only 
substantially intact radiation of metatherian 
mammals in the New World, where they con- 
stitute a distinctive component of terrestrial 
vertebrate faunas in many tropical and sub- 
tropical habitats. Although certain aspects of 
didelphid classification have remained stable 
for many years, notably the generic taxono- 
my of the larger opossums, recent discover- 
ies have underscored our still very incom- 
plete knowledge of phylogenetic diversity 
and relationships among the smaller forms, 
especially the so-called “‘marmosines’’ (for- 
merly classified as, or allied with, Marmosa 
Gray, 1821). Such discoveries include highly 
divergent new clades (Voss et al., 2001; Voss 
and Jansa, 2003; Voss et al., 2004) and un- 
suspected species-level diversity concealed 
by traditional synonymies (Mustrangi and 
Patton, 1997; Voss et al., 2001; Patton and 
Costa, 2003). Both phenomena suggest that 
the current classification of small didelphids 
requires critical attention. 
The didelphid marsupial genus Marmo- 
sops was originally named by Matschie 
(1916) to contain 11 species, of which M. 
incanus (Lund, 1840) was designated as the 
type. Although Tate (1933) treated Marmo- 
sops as a junior synonym of Marmosa, he 
acknowledged that Matschie’s taxon corre- 
sponded to a diagnosable cluster of species 
(the “‘Noctivaga Group’’) that could logically 
be recognized as a subgenus. In the decades 
that followed, however, Marmosops contin- 
ued to be treated as a junior synonym of 
Marmosa, even in classifications that used 
subgeneric categories (e.g., Cabrera, 1958; 
Reig et al., 1985). The current recognition of 
Marmosops as a distinct taxon dates from 
Gardner and Creighton (1989), who raised all 
of Tate’s species groups of Marmosa to ge- 
neric rank. 
As currently recognized in the systematic 
literature, Marmosops includes 36 nominal 
taxa, of which 14 are considered to be valid 
species and 22 to be subspecies or junior 
synonyms (table 1). The geographic disper- 
sion of type localities (fig. 1) approximates 
the distribution of the genus itself, which 
ranges from Panama to southeastern Brazil. 
Species of Marmosops occur in lowland rain 
forests, lowland dry forests, and in montane 
(“‘cloud’’) forests to about 3000 m above sea 
level. Trapping studies suggest that these 
small (20-120 g) opossums are predomi- 
nantly understory species that are often taken 
on the ground or a few meters above the 
ground (e.g., on logs, branches, and lianas), 
but apparently never in the canopy (Mal- 
colm, 1991; Patton et al., 2000; Voss et al., 
2001; Cunha and Vieira, 2002; Vieira and 
Monteiro-Filho, 2003). Although alleged to 
be insectivorous or omnivorous (Emmons, 
1997; Mustrangi and Patton, 1997; Cordero, 
2001; Voss et al., 2001), no analyses of rel- 
evant dietary data have been published. In 
fact, the natural history of Marmosops re- 
mains almost completely unstudied despite 
the local abundance of some species in rel- 
atively accessible habitats. 
