phylogenetic relationships and classification of didelphid marsupials ...

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52 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 322 Fig. 21. Occlusal views of left upper molar rows illustrating taxonomic differences in relative widths of teeth (not drawn to the same scale). A, Caluromysiops irrupta (FMNH 84426); B, Caluromys philander (AMNH 267334); C, Glironia venusta (AMNH 71395); D, Marmosa regina (MVZ 190333); E, Marmosops impavidus (MUSM 13284); F, Lestodelphys halli (MMNH 15708). have usually been called ‘‘predilambdodont’’ (e.g., by Reig et al., 1987). Unfortunately, neither descriptor applies unambiguously to some didelphids (Goin, 1997), and certain taxa have been coded with contradictory character states in different phylogenetic datasets (e.g., Didelphis; see Reig et al., 1987 [character 1]; Wroe et al., 2000 [character 10]; Wible et al., 2001 [character 31]). Our observations agree with Johanson’s (1996), that the shape (linearity versus labial inflection) of this crest is correlated with its occlusal relief (apical height above the trigon basin), and we recognize an intermediate condition for taxa that do not conform with either traditionally recognized morphotype. Among didelphids, only Caluromysiops has a truly linear centrocrista on M1–M3. In this taxon, the apex of the centrocrista is essentially level with the floor of the trigon basin, clearly conforming to the predilambdodont condition defined by Johanson (1996). By contrast, the centrocrista is strongly inflected labially (buccally)—and therefore distinctly ‘-shaped—in Chacodelphys, Cryptonanus, Gracilinanus, Lestodelphys, Marmosa, Marmosops, Metachirus, Monodelphis, Thylamys, and Tlacuatzin. The apex of the crest is elevated well above the trigon floor in these taxa, which are unambiguously dilambdodont sensu Johanson (1996). The intermediate condition occurs in the seven remaining genera (Caluromys, Chironectes, Didelphis, Glironia, Hyladelphys, Lutreolina, Philander) in which the centrocrista has a weak labial inflection with a slightly elevated apex; these taxa can appropriately be described as weakly dilambdodont. In many didelphids—Caluromys, Caluromysiops, Glironia, Gracilinanus, Hyladelphys, Marmosa, Tlacuatzin, and some species of Cryptonanus and Marmosops—the preprotocrista passes labially around the base of the paracone to join with the anterolabial cingulum. This results in the formation of a continuous shelf along the anterior margin of the tooth (fig. 21A–D), and taxa possessing this feature are sometimes said to have a ‘‘complete’’ anterior cingulum (Archer, 1976b: 3) or to exhibit ‘‘double rank prevallum-postvallid shearing’’ (Cifelli, 1993: 213). In the alternative morphology—exhibited by Chacodelphys, Chironectes, Didelphis, Lestodelphys, Lutreolina, Metachirus, Monodelphis, Philander, Thylamys, and other species of Cryptonanus and Marmosops—the preprotocrista extends only to a point at or
2009 VOSS AND JANSA: DIDELPHID MARSUPIALS 53 TABLE 8 Upper Molar Measurements and Proportions a N b Widths (mm) c M1 M2 M3 M4 Ratio (M4/M1) Caluromys lanatus 5 2.87 3.09 3.01 2.44 0.85 Caluromys philander 5 2.52 2.84 2.90 2.37 0.94 Caluromysiops irrupta 5 2.99 3.21 3.06 2.48 0.83 Chacodelphys formosa 2 1.23 1.64 1.84 1.88 1.53 Chironectes minimus 5 4.04 4.69 5.33 5.34 1.32 Cryptonanus chacoensis 4 1.30 1.71 1.89 1.85 1.42 Cryptonanus unduaviensis 5 1.39 1.79 2.01 2.02 1.45 Didelphis albiventris 1 4.04 5.01 5.60 5.47 1.35 Didelphis marsupialis 3 4.73 5.50 6.04 6.02 1.27 Didelphis virginiana 5 4.59 5.50 6.54 6.99 1.52 Glironia venusta 4 1.92 2.36 2.56 2.47 1.29 Gracilinanus aceramarcae 4 1.20 1.51 1.64 1.69 1.41 Gracilinanus agilis 5 1.28 1.66 1.87 1.89 1.48 Gracilinanus emiliae 3 1.14 1.49 1.67 1.65 1.45 Gracilinanus microtarsus 4 1.30 1.66 1.84 1.86 1.43 Hyladelphys kalinowskii 5 0.96 1.14 1.26 1.21 1.26 Lestodelphys halli 5 1.80 2.40 2.73 2.97 1.65 Lutreolina crassicaudata 4 2.76 3.36 4.15 4.85 1.76 Marmosa (Marmosa) lepida 5 1.33 1.69 1.90 1.96 1.47 Marmosa (Marmosa) mexicana 5 1.44 1.82 2.08 2.26 1.57 Marmosa (Marmosa) murina 5 1.46 1.78 2.08 2.18 1.49 Marmosa (Marmosa) robinsoni 5 1.71 2.10 2.36 2.53 1.48 Marmosa (Marmosa) rubra 5 1.61 2.05 2.33 2.57 1.60 Marmosa (Micoureus) demerarae 5 1.98 2.51 2.82 2.81 1.42 Marmosa (Micoureus) paraguayana 3 2.11 2.65 3.01 3.06 1.45 Marmosa (Micoureus) regina 5 2.18 2.77 3.12 3.17 1.45 Marmosops impavidus 5 1.58 2.00 2.30 2.46 1.56 Marmosops incanus 4 1.74 2.18 2.42 2.69 1.55 Marmosops noctivagus 5 1.83 2.31 2.67 2.82 1.54 Marmosops parvidens 5 1.34 1.67 1.91 1.90 1.42 Marmosops pinheiroi 5 1.33 1.68 1.92 2.04 1.53 Metachirus nudicaudatus 5 2.84 3.29 3.69 3.62 1.27 Monodelphis brevicaudata 5 2.08 2.46 2.64 2.90 1.39 Monodelphis emiliae 5 1.85 2.21 2.34 2.57 1.39 Monodelphis peruviana 5 1.57 1.87 2.05 2.15 1.37 Monodelphis theresa 2 1.36 1.67 1.84 2.11 1.55 Philander frenatus 3 2.77 3.32 3.92 4.17 1.51 Philander mcilhennyi 3 3.53 4.15 4.71 4.99 1.41 Philander opossum 4 3.18 3.74 4.30 4.55 1.43 Thylamys macrurus 5 1.55 2.05 2.32 2.37 1.53 Thylamys pallidior 5 1.31 1.74 2.04 2.12 1.62 Thylamys pusillus 5 1.34 1.72 1.96 2.05 1.53 Thylamys venustus 5 1.37 1.78 2.00 2.10 1.53 Tlacuatzin canescens 5 1.54 1.98 2.28 2.33 1.51 a Teeth were measured with digital calipers while viewed under low magnification to ensure that the caliper jaws were consistently placed. b Sample size. c Molar width was measured from the stylar shelf (at or near the ‘‘A’’ position) to the lingual apex of the protocone. Tabulated values are sample means.
Page 1 and 2: PHYLOGENETIC RELATIONSHIPS AND CLAS
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