phylogenetic relationships and classification of didelphid marsupials ...

176 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 322
hypoconulid twinned with entoconid. . . . .
........................ Caluromys
8b. Pelage of head uniformly pale, without any
dark markings; dark scapular stripes present;
premaxillary rostral process absent; right and
left frontals fused (median suture incomplete);
sagittal crest well developed, extending
anteriorly to frontals; secondary foramen
ovale present; centrocrista linear, uninflected;
hypoconulid not twinned with entoconid...................
Caluromysiops
9a. Circumocular mask absent; tail shorter than
combined length of head and body, without
prehensile modifications; postorbital processes
absent or indistinct; premaxillary rostral
process absent; palatine and maxillary fenestrae
usually absent; maxillary and alisphenoid
in contact on orbital floor; secondary foramen
ovale absent or formed by medial bullar
lamina that does not span transverse canal
foramen; entoconid subequal to or smaller than
hypoconulid on m1–m3 (absent or indistinct in
worndentitions) ............Monodelphis
9b. Dark circumocular mask present (but narrow
and inconspicuous in some taxa); tail longer
or shorter than combined length of head and
body, with or without prehensile modifications;
distinct postorbital processes present or
absent; premaxillary rostral process present
or absent; palatine and maxillary fenestrae
present or absent; maxillary and alisphenoid
separated by palatine on orbital floor; secondary
foramen ovale absent or formed by
anteromedial bullar process spanning transverse
canal foramen; entoconid taller than
hypoconulid on m1–m3 (except in Chacodelphys)
..........................10
10a. Secondary foramen ovale usually present,
formed by anteromedial bullar process spanning
transverse canal foramen . . . . . . . . 11
10b. Secondary foramen ovale usually absent . .
..............................14
11a. Manual digits III and IV subequal in length;
tail always longer than combined length of
head and body; premaxillary rostral process
present; maxillary fenestrae usually present
(occasionally absent in one species); P2 and
P3 subequal in height . . . . . . . Gracilinanus
11b. Manual digit III longer than digit IV; tail
longer or shorter than head-and-body; premaxillary
rostral process present or absent;
maxillary fenestrae absent or, if present, then
P3tallerthanP2..................12
12a. Tail longer than combined length of head and
body, with scales in spiral series, never
incrassate; premaxillary rostral process present
(but short in a few species); maxillary
fenestrae absent; fenestra cochleae exposed;
P2 and P3 subequal in height. . . Marmosops
12b. Tail longer or shorter than head-and-body,
with scales (when distinct) in annular series,
incrassate (at least seasonally); premaxillary
rostral process absent; maxillary fenestrae
present or absent; fenestra cochleae concealed
in a sinus formed by rostral and caudal
tympanic processes of petrosal; P3 taller than
P2............................13
13a. Manual claws long, extending well beyond
fleshy apical pads of digits; pedal digit III
longer than digit IV; tail shorter than
combined length of head and body; ventral
surface of tail tip not modified for prehension;
nasals conspicuously wider posteriorly
than anteriorly; maxillary fenestrae absent;
stapes columelliform and imperforate or
microperforate; p3 taller than p2; hypoconid
lingual to protocone on m3, not labially
salient ................. Lestodelphys
13b. Manual claws short, not extending much, if
at all, beyond fleshy apical pads of digits;
pedal digit IV longer than digit III; tail longer
or shorter than combined length of head-andbody;
ventral surface of tail tip modified for
prehension in most species; nasals uniformly
narrow (not much wider posteriorly than
anteriorly), with subparallel lateral margins;
maxillary fenestrae present or absent; stapes
triangular with large obturator foramen; p2
and p3 subequal in height; hypoconid labially
salient on m3, not lingual to protoconid......................
Thylamys
14a. Manual digit III longer than manual digit IV;
tail shorter than combined length of head and
body; nasals narrow, with subparallel lateral
margins; maxillary fenestrae present; hypoconid
not labially salient on m3 (lingual to
protoconid). . . . . . . . . . . . . . Chacodelphys
14b. Manual digits III and IV subequal in length;
tail longer than head-and-body; nasals distinctly
wider posteriorly than anteriorly;
maxillary fenestrae absent (except in Tlacuatzin);
hypoconid labially salient on m3 (not
lingual to protoconid) . . . . . . . . . . . . . . 15
15a. Tail scales in annular series; rostral process of
premaxillae absent; palatine fenestrae present;
petrosal exposed on posterolateral surface
of braincase through fenestra in parietalsquamosal
suture; unworn C1 usually with
small accessory cusps; P3 taller than
P2.................... Cryptonanus
15b. Tail scales in annual or spiral series; rostral
process of premaxillae present or absent;
palatine fenestrae present or absent; petrosal
not exposed through fenestra in parietalsquamosal
suture (fenestra absent); C1 with-