phylogenetic relationships and classification of didelphid marsupials ...

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16 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 322 the frons [forehead] past the inner edge of each ear (not including it), and straight backward through scapulae and hips, where they again approach the median line of the body and merge with the tail. This pair of lines encloses the major part of the dorsal area of head and body, the color of the area being very dark brownish-gray or grayish fuscous. The fuscous area is pointed at front, projecting forward between the ears, and narrows again to a point as it merges with the dark color of the upper surface of the tail. The second [lateral] area, light gray in color, frequently tinged with buffy or yellowish, extends [on each side] between the dark dorsal region and the edge of the belly color at the normal transition line. Ventral color either buffy, grayish, or snowy white. The hair bases of the dorsal fur are heavily pigmented, usually dark gray (or grayish), in most didelphids, but species of Didelphis uniquely exhibit white dorsal underfur. The ventral pelage also exhibits noteworthy taxonomic variation among didelphids. In some species the ventral fur is ‘‘graybased,’’ a descriptor that applies when the individual hairs are grayish basally and abruptly paler (usually whitish, yellowish, or brownish) distally; the overall color of the ventral fur then depends on the degree to which the dark basal pigmentation shows through the paler superficial hue. In other species, the ventral fur is partially or entirely ‘‘self-colored,’’ a descriptor that applies when the individual hairs have the same pigmentation (usually whitish) from root to tip. Because marked differences in the patterning of gray-based versus self-colored ventral pelage can occur among closely related (congeneric) species, such variation is often described and illustrated in the revisionary taxonomic literature (e.g., Patton et al., 2000: fig. 41). However, the existence of numerous intermediate conditions spanning the entire range of taxonomic variation in ventral color patterns (e.g., from entirely gray-based to completely self-white ventral fur) precludes meaningful phylogenetic scoring of this character. Whereas most of the pelage colors (and color patterns) described above are preserved on museum skins that have been protected in dark cabinets from the bleaching effects of light, other colors that can be striking in life fade quickly after death. The ventral pelage of live Monodelphis emiliae, for example, has been described as ‘‘bright glowing violaceous pink’’ (Emmons, 1997: 34), a lurid hue that is not retained in any examined museum specimens. What little is known about such fugitive pigments (some of which fluoresce under ultraviolet light) was summarized by Pine et al. (1985). Most other marsupials have unremarkable body pelage that essentially resembles the common didelphid condition as described above, but postcranial vibrissae are reduced or absent in a few clades (Lyne, 1959) and peramelemorphians have stiff, dorsally grooved guard hairs (illustrated in cross section by Lyne and McMahon, 1951: figs. 51, 60) that impart a distinctively harsh, spinous texture to their fur. Most other marsupials also resemble didelphids in having unpatterned dorsal fur, although there are noteworthy examples of apparently convergent markings (e.g., those of Dromiciops somewhat resemble Chironectes’; Marshall, 1978b) and some strikingly divergent ones (e.g., the transverse sacral barring seen in Perameles gunnii; Lyne, 1951: pl. 1B). All examined outgroup taxa have dark dorsal underfur. WRIST: The wrists of males and females are morphologically similar and externally featureless in most didelphids, but striking sexual dimorphism is present in certain small arboreal and scansorial forms (Lunde and Schutt, 1999). Grossly enlarged glabrous tubercles supported internally by carpal ossifications are exhibited by large adult males of Cryptonanus, Gracilinanus, Marmosops, Tlacuatzin, and some species of Marmosa. Two distinct kinds of tubercles can be distinguished, consisting of lateral (‘‘ulnar’’) tubercles supported internally by the pisiform, and medial (‘‘radial’’) tubercles supported by the prepollex (op. cit.). Although some intraspecific variation in the development of carpal tubercles has been documented, most of it can be attributed to ontogeny: tubercles are consistently present in the largest adult male specimens of species in which such structures occur, whereas they may be lacking in some smaller (presumably younger) conspecific males. Lunde and Schutt (1999) plausibly suggest that these structures function as clasping devices during copulation.
2009 VOSS AND JANSA: DIDELPHID MARSUPIALS 17 Fig. 2. Sexually dimorphic wrist morphology of Marmosops pinheiroi. Adult males (left, AMNH 267346) possess an externally obvious lateral carpal tubercle that is supported internally by an enlarged pisiform bone (arrows); females (right, AMNH 267342) do not exhibit this trait.
Page 1 and 2: PHYLOGENETIC RELATIONSHIPS AND CLAS
Page 3 and 4: CONTENTS Abstract .................
Page 5 and 6: ABSTRACT This report summarizes a d
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