phylogenetic relationships and classification of didelphid marsupials ...

118 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 322
men ovale usually present), and not in
contact with rostral tympanic process of
petrosal. Anterior limb of ectotympanic
suspended indirectly from basicranium (by
malleus). Stapes usually triangular with large
obturator foramen but sometimes columellar
and imperforate (varies within species). Fenestra
cochleae exposed, not concealed by
rostral and caudal tympanic processes of
petrosal. Paroccipital process large, erect (not
adnate to petrosal) and projecting ventrally.
Dorsal margin of foramen magnum bordered
by exoccipitals only, incisura occipitalis
absent.
Two mental foramina usually present on
lateral surface of each hemimandible (one
foramen is present unilaterally in a single
examined specimen of D. albiventris); mandibular
angular process acute and strongly
inflected medially.
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; third upper premolar (P3) taller
than second (P2); P3 with posterior cutting
edge only; upper milk premolar (dP3) large
and molariform. Molars highly carnassialized
(postmetacristae conspicuously longer than
postprotocristae); relative widths M1 , M2
, M3 . M4 or M3 , M4; centrocrista only
weakly inflected labially on M1–M3; ectoflexus
shallow, indistinct, or absent on M1
and M2, but consistently deep and distinct on
M3; anterolabial cingulum and preprotocrista
discontinuous (anterior cingulum
incomplete) on M3; postprotocrista with
carnassial notch. Last upper tooth to erupt
is M4.
Lower incisors (i1–i4) without distinct
lingual cusps. Second lower premolar (p2)
much taller than p3; lower milk premolar
(dp3) with complete (tricuspid) trigonid.
Hypoconid labially salient on m3; hypoconulid
twinned with entoconid on m1–m3;
entoconid much taller than hypoconulid on
m1–m3.
DISTRIBUTION: Didelphis is a quintessentially
eurytopic genus that ranges from
southern Canada throughout most of North
America (except the Rockies, the northern
Great Plains, the Great Basin, the arid
southwest, north-central Mexico, and Baja
California; Hall, 1981), all of Central America,
and most of South America (to about
40uS latitude in central Argentina; Flores et
al., 2007). South American collection records
(mapped by Cerqueira and Tribe, 2008)
represent almost every non-desert tropical
and subtropical biome on the continent.
REMARKS: Despite contradictory or ambiguous
phylogenetic results from most
sequenced loci analyzed separately (table 14),
the monophyly of Didelphis is strongly
supported by parsimony and Bayesian analyses
of morphology (fig. 27), a concatenated
five-gene dataset (fig. 33), and combined
(nonmolecular + molecular) supermatrices
(figs. 35, 36). Revisionary studies of the
genus Didelphis in its modern sense were
initiated by Allen (1901, 1902) and continued
by Krumbiegel (1941), Gardner (1973), Cerqueira
(1985), and Lemos and Cerqueira
(2002). Useful summaries of morphological
characters that distinguish Didelphis species
in local faunas are provided by Mondolfi and
Pérez-Hernández (1984), Catzeflis et al.
(1997), Cerqueira and Lemos (2000), Flores
and Abdala (2001), and Ventura et al. (2002).
Analyses of mitochondrial DNA sequence
variation within and among South American
species were reported by Patton et al. (2000)
and Patton and Costa (2003).
Lutreolina Thomas, 1910
Figure 47
CONTENTS: crassicaudata Desmarest, 1804
(including crassicaudis Olfers, 1818; bonaria
Thomas, 1923; ferruginea Larrañaga, 1923;
lutrilla Thomas, 1923; macroura Desmoulins,
1824; paranalis Thomas, 1923; travassosi
Mirando-Ribeiro, 1936; and turneri Günther,
1879).
MORPHOLOGICAL DESCRIPTION: Combined
length of adult head and body ca. 240–
345 mm; adult weight ca. 300–800 g). Rhinarium
with one ventrolateral groove on
each side of median sulcus; head entirely pale
and unmarked (dark circumocular mask, pale
supraocular spots, and dark midrostral stripe
absent); throat gland absent. Dorsal pelage
unpatterned, usually some shade of yellowish