phylogenetic relationships and classification of didelphid marsupials ...

124 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 322
on their phylogenetic analysis (op. cit.:
fig. 2), it would be logical to recognize
fuscogriseus and canus as valid species, but
the authors reasonably cautioned against
facile taxonomic decisions based on the
results of analyzing a single maternally
inherited gene. Indeed, the genus clearly
requires a more comprehensive revisionary
treatment, with particular attention devoted
to obtaining analyzable character data from
hitherto unrepresented taxa (notably azarica,
crucialis, grisescens, melanurus, and pallidus).
Our placement of azarica in the synonymy of
P. frenatus uncritically follows Gardner
(2005), who also allocated nominal taxa not
treated by Patton and da Silva (1997) to the
synonymy of P. opossum. Although an
alternative species-level classification of Philander
proposed by Hershkovitz (1997) was
not based on any explicit analysis of specimen
data, it raised several issues not adequately
treated by other authors and drew
attention to the possible existence of undescribed
taxa. New species described by Lew et
al. (2006) and Flores et al. (2008) contribute
additional taxonomic complexities and underscore
the need for critical revisionary
work on this difficult genus.
The tiresome nomenclatural controversy
regarding the use of Philander Tiedemann,
1808, versus Metachirops Matschie, 1916, as
the correct generic name for the gray foureyed
opossums (Pine, 1973; Hershkovitz,
1976; Gardner, 1981) was made moot by a
recent ruling of the International Commission
on Zoological Nomenclature (ICZN,
1998) that definitively established the availability
of Philander from Brisson (1762).
Tribe Thylamyini Hershkovitz, 1992
CONTENTS: Chacodelphys, Cryptonanus,
Gracilinanus, Lestodelphys, Marmosops, and
Thylamys.
DIAGNOSIS: Members of the tribe Thylamyini
differ from all other didelphids by
having a fenestra in the parietal-squamosal
suture through which the petrosal is visible
on the lateral surface of the braincase.
Additionally, most thylamyines (Chacodelphys
and Cryptonanus are exceptions) differ
from otherwise similar marmosines by having
a secondary foramen ovale formed by an
anteromedial bullar process that spans the
transverse canal foramen.
REMARKS: The monophyly of Thylamyini
(without Chacodelphys, from which sequence
data are unavailable) is strongly supported
by parsimony, likelihood, and Bayesian
analyses of IRBP (fig. 28) and BRCA1
(fig. 31); by likelihood and Bayesian analyses
of DMP1 (fig. 29); and by Bayesian analysis
of RAG1 (fig. 30). It is also strongly
supported by all analyses of a concatenated
five-gene dataset (fig. 33), and by Bayesian
analysis of a combined (nonmolecular +
molecular) dataset that includes Chacodelphys.
The presence of a fenestra in the
parietal-squamosal suture (appendix 5) and
a uniquely derived insertion at the BRCA1
locus (fig. 31) both optimize as thylamyine
synapomorphies.
Apparently, the earliest family-group
name based on Thylamys is technically
available from Hershkovitz (1992b), who
erroneously attributed authorship of Thylamyinae
to Reig et al. (1987).
Chacodelphys Voss et al., 2004
CONTENTS: formosa Shamel, 1930 (including
muscula Shamel, 1930).
MORPHOLOGICAL DESCRIPTION: Combined
length of adult head and body 68 mm
(external measurements are only available
from the young adult holotype); adult weight
unknown but probably ca. 10 g. Rhinarial
morphology unknown (no fluid-preserved
specimens have been examined); dark circumocular
mask present but narrow and
inconspicuous; pale supraocular spot absent;
dark midrostral stripe absent; gular gland
present. Dorsal fur unpatterned, brownish,
somewhat darker middorsally than along
flanks, but pelage not distinctly tricolored;
dorsal underfur gray based; dorsal guard
hairs short and inconspicuous; ventral fur
gray-based buffy. Manus mesaxonic (dIII .
dIV); manual claws shorter than fleshy apical
pads of digits; manual plantar pads present,
but presence/absence of dermatoglyphs unknown;
central palmar surface of manus
densely covered with small convex tubercles;
occurrence of carpal tubercles unknown.
Pedal digits unwebbed; dIV slightly longer
than other pedal digits; plantar surface of