phylogenetic relationships and classification of didelphid marsupials ...

166 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 322
for a discussion of this character and its taxonomic
distribution.
Character 80: Malleus with long and sharply inflected
neck, well-developed lamina, and manubrium parallel
to anterior process (0); or with short and uninflected
neck, no lamina, and manubrium not parallel to
anterior process (1). See text for a discussion of this
character and its taxonomic distribution.
Character 81: Stapes triangular and bicrurate, perforated
by a large foramen (0); or stapes columelliform
and microperforate or imperforate (1). See
text for a discussion of this character and its
taxonomic distribution. Although Schmelzle et al.
(2005: character 12) scored Didelphis marsupialis as
having a columelliform stapes, most of the
specimens of D. marsupialis that we examined have
a triangular stapes with a large foramen.
Character 82: Lambdoid sesamoids absent (0); or
present (1). See text for a discussion of this
character and its taxonomic distribution.
Character 83: Dorsal margin of foramen magnum
formed by exoccipitals and supraoccipital, incisura
occipitalis present (0); or by exoccipitals only,
incisura occipitalis absent (1). Scoring criteria and
information about the distribution of these traits
among didelphid terminals were provided by Voss
and Jansa (2003: character 49). See text for
explanation of reworded state descriptions and
for comments about traits expressed by outgroup
taxa.
Character 84: Paroccipital process absent (0); small
and broadly adnate to the petrosal (1); or large,
erect and usually directed ventrally (2). This
character differs from Voss and Jansa’s (2003)
character 48 by including a new state (0) for
absence of the paroccipital process in Dromiciops.
See text for comments about traits expressed by
other outgroup taxa. Because state 1 is plausibly
intermediate to states 0 and 2, this character was
treated as ordered (0 « 1 « 2) in all of our
analyses.
Character 85: Mandible usually with one mental
foramen (0); or with two mental foramina (1); or
with three mental foramina (2). This character
differs from Voss and Jansa’s (2003) character 50
by including a new state for the three mental
foramina of Perameles gunni. See Jansa and Voss
(2005) for a discussion of polymorphism in
Hyladelphys, and the text of this report for
information about outgroup variation. Because
state 1 is plausibly intermediate to states 0 and 2,
this character was treated as ordered (0 « 1 « 2)
in all of our analyses.
Character 86: Angular process acute and strongly
inflected (0); or obtuse and weakly inflected (1).
Scoring criteria and information about the distribution
of these traits among didelphid terminals
were provided by Voss and Jansa (2003: character
51). See text for explanation of reworded state
descriptions and for comments about traits expressed
by outgroup taxa.
Character 87: Retromolar fossa imperforate (0); or
pierced by retrodental canal (1). See text for a
discussion of this character and its taxonomic
distribution.
Character 88: Masseteric foramen absent (0); or
present (1). See text for a discussion of this
character and its taxonomic distribution.
UPPER DENTITION
Character 89: First upper incisor styliform or
chisellike (0); or I1 mesiodistally expanded and
flat-crowned (1). See text for a discussion of this
character and its taxonomic distribution.
Character 90: Second through fourth upper incisors
with approximately symmetrical, rhomboidal crowns
bearing subequal anterior and posterior cutting edges
(0); or I2–I4 conspicuously asymmetrical, with
much longer anterior than posterior cutting edges
(1); or I2–I4 hatchet-shaped (2); or I2–I4 flatcrowned
(3). See text for a discussion of this
character and its taxonomic distribution. In the
absence of any compelling evidence for intermediacy
among these alternative conditions, this character
was treated as unordered in all of our
analyses.
Character 91: Fifth upper incisor present (0); or I5
absent (1). See text for a discussion of this
character and its taxonomic distribution.
Character 92: Fifth upper incisor similar to I4 (0); or
I5 caniniform and double-rooted (1). See text for a
discussion of this character and its taxonomic
distribution. This character was scored as inapplicable
(‘‘-’’) for taxa lacking I5.
Character 93: Upper canine alveolus occupies premaxillary-maxillary
suture (0); or C1 alveolus contained
entirely in maxillary bone (1). This character is
rephrased from Voss and Jansa (2003: character
30), who misleadingly described the same taxonomic
variation in terms of the presence or absence
of a premaxillary palatal process. See text for
comments about traits expressed by outgroup taxa.
Character 94: Upper canine simple, without distinct
accessory cusps (0); or with distinct posterior
accessory cusp (1); or with distinct anterior and
posterior accessory cusps (2); or with distinct
anterior accessory cusp (3). This character is
restructured from Voss and Jansa’s (2003) character
53, which treated states 0, 1, and 2 as stages of
an ordered transformation series. The discovery of
another condition (state 3) among the outgroup
taxa of this study introduced another hypothetically
intermediate condition between the absence of
any accessory cusps and the presence of both
anterior and posterior accessory cusps. Although
this could be accommodated by a step matrix, we
have also observed dentitions with indistinct
anterior and posterior accessory cusps, suggesting
that transitions between states 0 and 2 need not
involve states 1 or 3 as intermediate stages.
Therefore, we now treat this character as unordered.
We scored sexual dimorphism in canine
morphology in caenolestids as polymorphisms (0/3
for Caenolestes, 0/2 for Rhyncholestes; see text).
Character 95: First upper premolar (P1) large, at least
one-half the height or width of P2 (0); or vestigial,
less than one-third the height or width of P2, or
absent (1). Scoring criteria and information about