10 AMERICAN MUSEUM NOVITATES 


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NO. 3466 

Dorsal views of right forefeet of Marmosops incanus (A, MVZ 197629) and Marmosa 
robinsoni (B, AMNH 259983) illustrating generic differences in digital proportions. Species of Mar- 
mosops have mesaxonic forefeet in which digit III is longer than all of the other manual digits and digit 
V is short (about equal in length to digit I). By contrast, species of Marmosa (and Gracilinanus) have 
paraxonic forefeet in which digits II] and IV are subequal and digit V is long. 
annular series (Voss and Jansa, 2003: char- 
acter 23). Lastly, the central hair of each cau- 
dal-scale triplet is petiolate, thicker, and usu- 
ally more heavily pigmented than the lateral 
hairs in Marmosops, whereas the central hair 
is not conspicuously differentiated from the 
lateral hairs in Gracilinanus (Voss and Jansa, 
2003: character 27). 
Cranially, Marmosops consistently lacks 
maxillary fenestrae, palatal openings that are 
consistently present in Gracilinanus on each 
side of the maxillopalatine openings near the 
M1/M2 commissure (fig. 8). The morpholo- 
gy of the deciduous lower premolar (dp3) 
might also distinguish these taxa, but we 
have examined so few juvenile Gracilinanus 
(two specimens of G. agilis and one G. em- 
iliae, all with incomplete trigonids) that the 
diagnostic value of this trait is unclear. 
COMPARISONS WITH THYLAMYS: Specimens 
of Marmosops have occasionally been mis- 
identified as Thylamys despite the large num- 
ber of consistent differences that distinguish 
these very dissimilar taxa. Whereas the dor- 
sal body pelage of Marmosops is uniformly 
colored and unpatterned, the middorsum of 
Thylamys is distinctly darker than the flanks, 
with a more-or-less sharp line of transition 
between the two colors on either side (Voss 
and Jansa, 2003: character 7). Additional ex- 
ternal differences (table 2) include the mor- 
phology of the central palmar surface of the 
manus (Voss and Jansa, 2003: character 11), 
the occurrence of lateral carpal tubercles 
(Voss and Jansa, 2003: character 12), occur- 
rence of plantar pelage on the tarsus (Voss 
and Jansa, 2003: character 16), caudal hair 
morphology (Voss and Jansa, 2003: character 
27), and caudal incrassation (Voss and Jansa, 
2003: character 28). Craniodental differences 
between these genera are likewise numerous, 
including the presence/absence of a rostral 
premaxillary process (Voss and Jansa, 2003: 
character 29), shape of the nasal bones (Voss 
and Jansa, 2003: character 33), size and ex- 
tent of the posterolateral palatal foramina 
(Voss and Jansa, 2003: character 41), lateral 
exposure of the fenestra cochleae (Voss and 
Jansa, 2003: character 47), and upper pre- 
molar proportions (Voss and Jansa, 2003: 
character 55). 
PHYLOGENETIC STATUS AND RELATIONSHIPS: 
Although distinguished from certain other 
‘““marmosines”’ by a relatively small number 
