phylogenetic relationships and classification of didelphid marsupials ...

128 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 322
ular nerve (secondary foramen ovale absent),
and not contacting rostral tympanic process
of petrosal. Anterior limb of ectotympanic
directly suspended from basicranium. Stapes
triangular, perforated by large obturator
foramen. Fenestra cochleae exposed, not
concealed by rostral and caudal tympanic
processes of petrosal. Paroccipital process
small, adnate to petrosal. Dorsal margin of
foramen magnum formed by supraoccipital
and exoccipitals, incisura occipitalis present.
Two mental foramina present on lateral
surface of each hemimandible; angular process
acute and strongly inflected.
Unworn crowns of I2–I5 symmetrically
rhomboidal (‘‘premolariform’’), with subequal
anterior and posterior cutting edges,
slightly increasing in length (mesiodistal
dimension) from I2 to I5. Upper canine
(C1) alveolus in premaxillary-maxillary suture;
C1 usually with one or two small
accessory cusps (the posterior accessory cusp
is more consistently distinct than the anterior
cusp). First upper premolar (P1) smaller than
posterior premolars but well formed and not
vestigial; third upper premolar (P3) taller
than P2; P3 with posterior cutting edge only;
upper milk premolar (dP3) large and molariform.
Upper molars strongly carnassialized
(postmetacristae conspicuously longer than
postprotocristae); relative widths M1 , M2
, M3 . M4 or M1 , M2 , M3 , M4;
centrocrista strongly inflected labially on
M1–M3; ectoflexus shallow or absent on
M1, deeper on M2, and consistently deep on
M3; anterolabial cingulum continuous with
preprotocrista (complete anterior cingulum
present) on M3 in some species (e.g., C.
unduaviensis) but anterolabial cingulum and
preprotocrista discontinuous (anterior cingulum
incomplete) on M3 in others (e.g., C.
chacoensis); postprotocrista without carnassial
notch. Last upper tooth to erupt is P3.
Lower incisors (i1–i4) with distinct lingual
cusps. Lower canine (c1) procumbent, with
flattened bladelike apex, usually with small
posterior accessory cusp (but often absent on
even moderately worn teeth). Second lower
premolar (p2) taller than p3; lower milk
premolar (dp3) with complete trigonid (tricuspid
in in C. chacoensis) or with incomplete
trigonid (bicuspid in C. unduaviensis). Hypoconid
labially salient (level with labial apex of
protoconid) on m3; hypoconulid twinned
with entoconid on m1–m3; entoconid much
taller than hypoconulid on m1–m3.
DISTRIBUTION: Cryptonanus is known from
mostly unforested tropical and subtropical
biomes south of the Amazon River and east
of the Andes, including the Caatinga, Cerrado,
Chaco, and northern Pampas; collection
localities mapped by Voss et al. (2005)
and D’Elía and Martínez (2006) are from
Paraguay, Uruguay, eastern Bolivia, northern
Argentina, and eastern Brazil.
REMARKS: Our species-level taxonomy of
Cryptonanus follows Voss et al. (2005) who,
however, cautioned that this arrangement is
provisional and unsupported by rigorous
tests of species limits. In particular, the
genetic distinctness of C. agricolai, C. chacoensis,
C. ignitus, and C. unduaviensis is not
overwhelmingly indicated by available morphological
data and merits careful evaluation.
Molecular sequence comparisons would
be an especially welcome supplement to the
scant phenotypic evidence at hand.
Gracilinanus Gardner and Creighton, 1989
Figure 50
CONTENTS: aceramarcae Tate, 1931; agilis
Burmeister, 1854 (including beatrix Thomas,
1910; buenavistae Tate, 1931; and peruana
Tate, 1931); dryas Thomas, 1898; emiliae
Thomas, 1909 (including longicaudus Hershkovitz,
1992); marica Thomas, 1898 (including
perijae Hershkovitz, 1992); and microtarsus
Wagner (1842).
MORPHOLOGICAL DESCRIPTION: Combined
length of adult head and body ca. 75–
130 mm; adult weight ca. 10–50 g. Rhinarium
with two ventrolateral grooves on each
side of median sulcus; dark circumocular
mask present; pale supraocular spot absent;
dark midrostral stripe absent; throat gland
present in adult males. Dorsal pelage unpatterned
reddish or grayish brown with
dark-gray hair bases; dorsal guard hairs
short and inconspicuous; ventral fur mostly
gray-based buff or orange (e.g., in G.
microtarsus), but self-white in some species
(e.g., G. emiliae). Manus paraxonic (dIII 5
dIV); manual claws small, not extending
beyond fleshy apical pads of digits; dermatoglyph-bearing
manual plantar pads