phylogenetic relationships and classification of didelphid marsupials ...

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14 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 322 Fig. 1. Ventral view of rhinarium in Thylamys pallidior (A, UMMZ 156349) and Marmosa robinsoni (B, UMMZ 117236). Both species have a broad pars supralabialis (psl) that contacts the upper lip. Only a single groove (g) is present along the ventral margin of the pars supralabialis on each side of the median sulcus (ms) inT. pallidior, whereas two ventrolateral grooves are present in M. robinsoni. Scale bars 5 2 mm. beled illustrations of didelphid facial vibrissae are provided by Pocock (1914: fig. 1A) and Lyne (1959: fig. 2). Most other plesiomorphic marsupials closely resemble didelphids in cranial vibrissal traits, but caenolestids lack interramal vibrissae (Lyne, 1959). Didelphids exhibit conspicuous taxonomic variation in facial markings (frontispiece; Voss and Jansa, 2003: fig. 3). In Caluromys, a median streak of dark fur, unconnected with any other dark marking, extends from the rostrum to the frontal region. In other didelphids, a chevron of dark coronal fur sometimes extends anteriorly between the ears and down the rostral midline, but the condition seen in Caluromys is distinctive and apparently nonhomologous. No nondidelphid marsupial that we examined has a dark midrostral stripe. The fur surrounding the eye is not distinctively colored in Caluromysiops, Lutreolina, or Monodelphis, but most other didelphids have masklike markings. A circumocular mask or ring of dark (usually blackish) fur that contrasts sharply with the paler (usually brownish, whitish, or grayish) color of the crown and cheeks is present in Glironia, Lestodelphys, and ‘‘marmosines’’ (taxa formerly included in ‘‘Marmosa’’ sensu Tate, 1933). Species of Caluromys have essentially similar reddish-brown eye rings that contrast with grayish cheeks and crowns. A blackish mask is likewise present in all examined species of Didelphis, but this marking is inconspicuous in D. marsupialis and D. virginiana. A blackish mask is also present in Metachirus, Chironectes, and Philander, but the dark circumocular fur in these taxa is usually continuous with dark fur on the crown of the head. Among nondidelphid marsupials, dark circumocular masks are present in Dromiciops, some dasyurids (e.g., Sminthopsis crassicaudata), a few peramelemorphians (e.g., Echymipera kalubu), and some small arboreal diprotodontians (e.g., Petaurus breviceps); only one examined outgroup taxon, Echymipera kalubu, has a mask that is more or less continuous with dark coronal fur. A distinct whitish supraocular spot is consistently present in species of Metachirus and Philander, resulting in the ‘‘four-eyed’’ marking by which these animals are commonly known. Most other didelphids lack pale supraocular markings. (An indistinct pale bar above each eye in Chironectes appears to be part of the unique transverse banding pattern in that taxon rather than a homologue of the condition seen in Metachirus and Philander.) We have not examined any nondidelphid marsupial with pale supraocular spots. GULAR GLAND: As described by Tate (1933: 30), many didelphids have a cutaneous
2009 VOSS AND JANSA: DIDELPHID MARSUPIALS 15 gular (throat) gland, the presence of which is indicated on dried skins and fluid-preserved specimens by a bare median patch of skin; often, but not invariably, the surrounding fur is discolored. According to Barnes (1977: 390), this secretory region contains ‘‘hypertrophied apocrine sudoriferous glands and sebaceous glands, both confined to the thickened dermis.’’ External signs of glandular activity tend to be maximally developed in fully mature males (loc. cit.). No unambiguously glandular throat patch was observed in any examined specimens of Caluromys, Caluromysiops, Chironectes, Hyladelphys, Lutreolina, Philander, orTlacuatzin. By contrast, fully adult male specimens of Cryptonanus, Gracilinanus, Lestodelphys, and Thylamys usually exhibit well-developed gular glands. A gular gland is also present on the young adult male holotype (and only known skin) of Chacodelphys formosa. Other didelphid genera (Marmosa, Marmosops, and Monodelphis) include some species that consistently develop adult male gular glands and others that just as consistently show no trace of such organs (Voss and Jansa, 2003). Although adult male Didelphis often have discolored gular fur, no glandular skin is macroscopically distinguishable. Because we were not able to examine any fully adult male specimens of Glironia, the occurrence of gular glands in this taxon is unknown. Gular (or sternal) glands that are macroscopically and histologically similar to those of didelphids are present in most dasyurids (Cooper et al., 2005), but other plesiomorphic outgroup taxa (e.g., caenolestids, peramelids, Dromiciops) seem to lack all external traces of glandular activity on the throat or chest. BODY PELAGE: All didelphids have one or more tracts of postcranial vibrissae (Brown and Yalden, 1973), including ulnar-carpal vibrissae (at the wrist), medial antebrachial vibrissae (at or near the middle of the forearm), anconeal vibrissae (at the elbow), and/or calcaneal vibrissae (on the ankle). Lyne (1959) reported the occurrence of postcranial vibrissae in several didelphid species based on his examination of pouch young, whose sensory hair follicles are easily seen because they are not obscured by coat hairs. Unfortunately, postcranial vibrissae are much harder to observe on fully furred adult specimens, the only material commonly available for most species. We found ulnarcarpal and medial antebrachial vibrissae on most examined didelphids, whereas anconeal and calcaneal vibrissae were often inapparent. All didelphids have soft (nonspinous) fur consisting of two or more distinct types of hairs whose density and morphology determine the appearance and texture of the coat. Some taxa (e.g., Caluromys) have somewhat woolly fur that does not lie flat or exhibit the glossy highlights typically seen in the pelts of many other taxa, but textural differences are hard to define by objective criteria that can be used for character-state definitions or taxonomic diagnoses. The only structural (nonpigmental) feature of didelphid body pelage that seems useful in this context is the presence of uniquely long, coarse guard hairs that project conspicuously from the underfur in species of Didelphis. The dorsal body pelage of most didelphids is uniformly colored and unpatterned, usually some shade of brownish or grayish, but some taxa are distinctively marked (see illustrations in Eisenberg, 1989; Redford and Eisenberg, 1992; Pérez-Hernández et al., 1994; Reid, 1997; Eisenberg and Redford, 1999). Blackish transverse bars connected middorsally on a pale-grayish background, for example, characterize Chironectes; dark scapular stripes are unique to Caluromysiops; three longitudinal stripes are present in several species of Monodelphis (e.g., M. theresa); a grayish middorsum contrasting with reddish flanks is exhibited by other species in that genus (e.g., M. brevicaudata); and a grayish midbody contrasting with reddish head and rump is seen in others (e.g., M. emiliae). The subtle but consistently diagnostic ‘‘tricolor’’ shading of Thylamys and Lestodelphys was described by Tate (1933: 209): Instead of the usual bicolor system composed of a dorsal color, paling a little on the sides, which is replaced at a generally well-marked transition line by a distinct ventral color, the elegans group [5 Thylamys] displays three distinct shades, separated from each other along each side by two lines of transition. The additional lines are subdorsal, running from a point at the center of
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Page 3 and 4: CONTENTS Abstract .................
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phylogenetic relationships and classification of didelphid marsupials ...

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