phylogenetic relationships and classification of didelphid marsupials ...

100 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 322
DISTRIBUTION: Currently known from fewer
than a dozen specimens, Hyladelphys has
been reported from just nine localities in
the rainforested lowlands of eastern Peru,
central Amazonian Brazil, southern Guyana,
and French Guiana (Astúa, 2007). Extrapolating
from these scanty data is obviously
problematic, but it would not be surprising
to find this elusive taxon anywhere in
Amazonia.
REMARKS: High levels of molecular divergence
between sequenced specimens of Hyladelphys
from French Guiana and Peru,
together with geographic variation in morphological
characters, suggest that additional
species remain to be described in this genus
(Jansa and Voss, 2005).
Subfamily Didelphinae Gray, 1821
CONTENTS: Marmosini, Metachirini, Didelphini,
and Thylamyini.
DIAGNOSIS: Members of this clade uniquely
differ from other didelphids by lacking an
anterior cutting edge on P3 (the third upper
premolar is double bladed in all basal
didelphids). In addition, Didelphinae differs
from Glironiinae by having a caudal dorsum
that is macroscopically naked, at least near
the tip; an unpaired median teat; welldeveloped
posterolateral palatal corners;
and postorbital processes that (when present)
are formed only by the frontals. Didelphinae
additionally differs from Caluromyinae by
having a shorter fourth manual digit (dIII is
subequal to or longer than dIV), an incompletely
ossified palate (maxillopalatine and
sometimes other fenestrae are invariably
present), transverse canal foramina, a wide
gap between the alisphenoid tympanic process
and the rostral tympanic process of the
petrosal, an acute and strongly inflected
mandibular angle, an upper canine alveolus
that lies within the premaxillary-maxillary
suture, a nonvestigial P1, a larger P3 (subequal
to or taller than P2), and a distinct
ectoflexus on M3. Didelphinae additionally
differs from Hyladelphinae by having an
unpaired median teat, nonvestigial milk
teeth, and a larger P3 (subequal to or taller
than P2).
REMARKS: The monophyly of Didelphinae
is strongly supported by all analyses of
BRCA1 sequences (fig. 31), concatenated
sequence data from five genes (fig. 33), and
combined (nonmolecular + molecular) data
when Chacodelphys is excluded (fig. 35).
Subfamilial monophyly is also supported by
a uniquely shared insertion (not coded for
phylogenetic analysis) at the BRCA1 locus
(fig. 31). However, only two morphological
traits optimize as unambiguous synapomorphies
of Didelphinae: an unpaired median
teat and a strongly labially inflected centrocrista
(subsequently reversed in Didelphini;
appendix 5). In addition to genera referred to
the tribes named above, the genus {Hyperdidelphys
(here unassigned to tribe) clearly
belongs to this subfamily based on characters
described and illustrated by Goin and Pardiñas
(1996) and others subsequently scored for
phylogenetic analysis by D.A. Flores and the
senior author.
Tribe Marmosini Hershkovitz, 1992
CONTENTS: Marmosa, Monodelphis, {Thylatheridium,
andTlacuatzin.
DIAGNOSIS: Marmosines can be distinguished
from other members of the subfamily
Didelphinae by lacking a pouch (present in
all Didelphini), by lacking an anteromedial
bullar process spanning the transverse canal
foramen (present in Metachirini and most
Thylamyini), by lacking a fenestra in the
squamosal-parietal suture (present in most
Thylamyini), and by having the supraoccipital
form part of the dorsal margin of the
foramen magnum (absent in adult Metachirini
and most adult Didelphini).
REMARKS: The monophyly of Marmosini
as construed herein is strongly supported by
all analyses of BRCA1 (fig. 31), vWF
(fig. 32), concatenated sequence data from
five genes (fig. 33), and our combined (nonmolecular
+ molecular) dataset excluding
Chacodelphys (fig. 35). However, no morphological
trait optimizes as an unambiguous
synapomorphy of this molecularly robust
clade. Instead, all of the diagnostic features
listed above appear to be plesiomorphic
within the subfamily Didelphinae.
Although the name Marmosini was used
by Reig et al. (1985, 1987) it was not
accompanied by an explicit statement of
taxonomically differentiating characters. To