phylogenetic relationships and classification of didelphid marsupials ...

2009 VOSS AND JANSA: DIDELPHID MARSUPIALS 97
posterior cutting edges. Upper canine (C1)
alveolus contained entirely within maxillary
bone; C1 simple (without accessory cusps),
and very large in adult specimens. First upper
premolar (P1) absent or minute and vestigial;
second upper premolar (P2) much taller than
P3; P3 with both anterior and posterior
cutting edges; upper milk premolar (dP3)
large and molariform. Molars not carnassialized
(postmetacristae subequal to postprotocristae);
relative widths M1 , M2 . M3 .
M4; centrocrista straight (uninflected) on
M1–M3; ectoflexus absent on all upper
molars; 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)
much taller than p3; lower milk premolar
(dp3) large and nonvestigial, but paraconid
not well developed (trigonid incomplete).
Hypoconid labially salient on m3; hypoconulid
not twinned with entoconid on any lower
molar; entoconid much taller than hypoconulid
on m1–m3.
DISTRIBUTION: Caluromysiops is currently
known from just seven localities in the
rainforested Amazonian lowlands of southeastern
Colombia, eastern Peru and western
Brazil (Emmons, 2008).
REMARKS: Various authors (e.g., Cabrera,
1958; Simpson, 1972; Izor and Pine, 1987)
have questioned whether it is useful to
separate Caluromysiops from Caluromys,
but none explicitly considered the suite of
trenchant morphological characters that distinguish
these taxa. Among other features,
Caluromysiops differs from Caluromys by its
lack of a circumocular mask and dark
midrostral stripe, presence of dark scapular
stripes, shorter tail (table 5), absence of a
premaxillary rostral process, co-ossified frontals,
presence of a well-developed sagittal
crest, presence of a secondary foramen ovale,
globular (versus conical) alisphenoid bullae,
columelliform stapes, linear centrocrista, and
untwinned hypoconulid. Although there is no
cladistic problem with combining these taxa
under a single generic name, maintaining
current binomial usage is likewise unobjectionable
and serves to separate the monophyletic
cluster of species currently known as
Caluromys from its long-branched sister
taxon.
Subfamily Hyladelphinae, new
CONTENTS: Hyladelphys.
DIAGNOSIS: Members of this clade uniquely
differ from other didelphids by their
vestigial milk dentition (dP3/dp3 are large,
more or less molariform teeth in other
opossums; Voss et al., 2001: table 5).
Additional contrasts among hyladelphines
and members of other didelphid subfamilies
were tabulated by Jansa and Voss (2005:
table 2).
REMARKS: Given the phylogenetic results
at hand, a monotypic suprageneric taxon for
Hyladelphys could either be ranked as a
subfamily (as it is here) or as a tribe (if the
genus were referred to the Didelphinae).
Although the issue of rank is not biologically
meaningful, the former option serves to
emphasize the intermediate position of this
odd little opossum between basal didelphids
(Glironia and caluromyines) and the speciose
radiation of lineages that are more closely
related to Didelphis. The branch leading to
Hyladelphys is very long in most molecular
reconstructions of didelphid anagenesis (e.g.,
fig. 33), suggesting an ancient history of
independent evolution accompanied by extinction
of transitional forms; the same
conclusion is suggested by its uniquely
reduced milk dentition and by characters of
the postcranial skeleton (Flores, 2009). In
effect, excluding Hyladelphys from Didelphinae
simplifies the diagnosis of the latter clade
and provides a new higher taxon to accommodate
fossil relatives of the former, should
any be discovered.
Hyladelphys Voss et al., 2001
Figure 40
CONTENTS: kalinowskii Hershkovitz, 1992.
MORPHOLOGICAL DESCRIPTION: Combined
adult length of head and body ca. 75–95 mm;
adult weight ca. 10–20 g. Rhinarium with
two ventrolateral grooves on each side of
median sulcus; dark circumocular mask