re AMERICAN MUSEUM NOVITATES 
NO. 3466 

Fig.5: 
Lateral view of posterior braincase in Marmosops impavidus (A, AMNH 272709) and Mar- 
mosa murina (B, AMNH 272816) illustrating the presence of a fenestra (fen) that exposes the petrosal 
(pet) between the parietal (par) and squamosal (sq) in the former taxon. The petrosal is not laterally 
exposed by a fenestra between the parietal and squamosal in Marmosa. 
68°05'W; 2500 m above sea level) in the val- 
ley of the Rio Zongo, Departamento La Paz, 
Bolivia. The holotype is a whole (unskinned) 
fluid-preserved specimen with an extracted 
skull and mandibles. 
PARATYPES: Five additional specimens 
(listed as unidentified ““Marmosa” by An- 
derson, 1997: 151) were collected by G.K. 
Creighton in 1979 at two adjacent localities 
in the valley of the Rio Zongo, Departmento 
La Paz, Bolivia. Two of these (UMMZ 
155999, 156000) were taken above the type 
locality near the Cuticucho hydroelectric 
generating station (ca. 16°08’S, 68°07'W) at 
a recorded elevation of 2967 m, whereas 
three others (UMMZ 156001—156003) were 
trapped below the type locality at a recorded 
elevation of 2000 m. All five paratypes are 
adult animals preserved as whole (unskin- 
ned) fluids with extracted skulls and mandi- 
bles. 
DISTRIBUTION: Known only from wet mon- 
tane forest in the valley of the Rio Zongo, 
Departamento La Paz, Bolivia, between 2000 
and 3000 m above sea level (fig. 10). 
EtTyMoLocy: For G. Ken Creighton, col- 
lector of the first known specimens of this 
species and author of the first modern anal- 
ysis of didelphid phylogeny based on mor- 
phological characters (Creighton, 1984). 
DESCRIPTION: Marmosops creightoni is a 
medium-sized species (see table 3 for mea- 
surements and weights), much larger than 
members of the M. parvidens group (ca. 20— 
35 g adult weight; Voss et al., 2001: tables 
9, 10) but substantially smaller than some 
lowland forms like M. incanus (adults of 
which can weigh as much as 120 g; Lorini 
et al., 1994). The body pelage is almost en- 
tirely dark, the colors probably somewhat 
faded in our fluid-preserved specimens, but 
still a rich chocolate-brown dorsally on the 
holotype (collected in 1999) and only a little 
more bleached on the 24-year-old paratypes. 
The ventral body coloration is slightly paler 
brown, but there is no sharp distinction be- 
tween dorsal and ventral color zones, and all 
of the thoracic and abdominal fur is gray- 
based. The chin is self-white in all of the 
material at hand, and white fur extends pos- 
teriorly onto the throat of one paratype 
(UMMZ 155601). The blackish mask that 
surrounds the eye on each side of the head 
does not extend anteriorly to include the 
mystacial pads (which are covered with short 
brownish fur) or posteriorly to the base of 
the ears. The mystacial and genal vibrissae 
are blackish, whereas the submental and in- 
terramal hairs are white. The pinnae are uni- 
formly dark and appear naked (a sparse au- 
