phylogenetic relationships and classification of didelphid marsupials ...

2009 VOSS AND JANSA: DIDELPHID MARSUPIALS 99
present, extending posteriorly from mystacial
region to base of ear on each side of face; pale
supraocular spot absent; dark midrostral
stripe absent; throat gland absent. Dorsal
pelage unpatterned reddish-brown with darkgray
hair bases; dorsal guard hairs short and
inconspicuous; ventral fur self-white. Manus
paraxonic (dIII 5 dIV); manual claws
relatively large, strongly recurved, and slightly
longer than fleshy apical pads of digits;
dermatoglyph-bearing manual plantar pads
present; central palmar epithelium smooth or
sparsely tubercular; carpal tubercles absent.
Pedal digits unwebbed; dIV longer than other
pedal digits; plantar surface of heel naked.
Pouch absent; mammae 2–0–2 5 4, all
abdominal-inguinal; cloaca present. Tail
much longer than combined length of head
and body, slender and muscular (not incrassate),
and apparently naked (without a
conspicuously furred base); caudal scales in
both annular and spiral series, each scale with
three subequal bristle-like hairs emerging
from distal margin; ventral caudal surface
modified for prehension distally, with apical
pad bearing dermatoglyphs.
Premaxillary rostral process absent. Nasals
long, extending anteriorly above I1 (concealing
most of nasal orifice from dorsal view),
and conspicuously widened posteriorly near
maxillary-frontal suture. Maxillary turbinals
elaborately branched. Lacrimal foramina
exposed laterally on or near anterior orbital
margin, one or two on each side. Orbits very
large; interorbital region strongly convergent
anteriorly, with beaded dorsolateral margins;
postorbital processes absent. Left and right
frontals and parietals separated by persistent
median sutures. Parietal and alisphenoid in
contact on lateral braincase (no frontalsquamosal
contact). Sagittal crest absent.
Petrosal not exposed laterally through fenestra
in parietal-squamosal suture (fenestra
absent). Parietal-mastoid contact present
(interparietal does not contact squamosal).
Maxillopalatine fenestrae present; palatine
and maxillary fenestrae absent; posterolateral
palatal foramina small, not extending anteriorly
between M4 protocones. Posterior palatal
morphology more Didelphis-like than
Caluromys-like (with moderately well-developed
posterolateral corners, the internal
choanae distinctly constricted behind). Max-
illary and alisphenoid bones not in contact
on floor of orbit (widely separated by
palatine). Transverse canal foramen present.
Alisphenoid tympanic process smoothly
globular, without anteromedial process or
posteromedial lamina (secondary foramen
ovale absent), and not in contact with rostral
tympanic process of petrosal. Anterior limb
of ectotympanic suspended directly from
basicranium. Stapes triangular with large
obturator foramen. Fenestra cochleae exposed,
not concealed by rostral and caudal
tympanic processes of petrosal. Paroccipital
process small and adnate to petrosal. Dorsal
margin of foramen magnum bordered by
supraoccipital and exoccipitals, incisura occipitalis
present.
One or two mental foramina present on
lateral surface of each hemimandible; angular
process acute and strongly inflected.
Unworn crowns of I2–I5 asymmetrical
(‘‘incisiform’’), with much longer anterior
than posterior cutting edges. Upper canine
(C1) alveolus in premaxillary-maxillary suture;
C1 simple, without accessory cusps.
First upper premolar (P1) smaller than
posterior premolars but well formed and
not vestigial; second upper premolar (P2)
much taller than P3; P3 with both anterior
and posterior cutting edges; milk premolar
(dP3) very small, vestigial, and lacking
distinct occlusal features. Upper molars not
strongly carnassialized (postmetacristae only
slightly longer than postprotocristae); relative
widths M1 , M2 , M3 . M4; centrocrista
weakly inflected labially on M1–M3; ectoflexus
indistinct on M1, shallow on M2,
distinct on M3; anterolabial cingulum continuous
with preprotocrista (complete anterior
cingulum present) on M3; postprotocrista
without carnassial notch. Last upper
tooth to erupt is P3.
Lower incisors (i1–i4) with distinct lingual
cusps. Lower canine (c1) erect, acutely
pointed, and simple (without a posterior
accessory cusp). Second lower premolar (p2)
taller than p3; lower milk premolar (dp3)
small, vestigial, and lacking distinct occlusal
features. Hypoconid labially salient on m3;
hypoconulid twinned with entoconid on m1–
m3; entoconid taller than hypoconulid on
m1–m3.