phylogenetic relationships and classification of didelphid marsupials ...

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104 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 322 usually unilateral variants in some species); angular process acute and strongly inflected. Unworn crowns of I2–I5 symmetrically rhomboidal (‘‘premolariform’’), with subequal anterior and posterior cutting edges, and increasing in length (mesiodistal dimension) from I2 to I5. Upper canine (C1) alveolus in premaxillary-maxillary suture; C1 simple (without accessory cusps in most species) or with posterior accessory cusp only (in M. lepida). First upper premolar (P1) smaller than posterior premolars but well formed and not vestigial; second and third upper premolars (P2 and P3) subequal in height; P3 with posterior cutting edge only; upper milk premolar (dP3) large and molariform. Molars moderately carnassialized (postmetacristae are visibly longer than postprotocristae); relative widths usually M1 , M2 , M3 , M4; centrocrista strongly inflected labially on M1–M3; ectoflexus indistinct or absent on M1, shallow but usually distinct on M2, and consistently deep on M3; anterolabial cingulum continuous with preprotocrista (complete anterior cingulum present) on M3. Last upper tooth to erupt is P3. Lower incisors (i1–i4) with distinct lingual cusps. Unworn lower canine (c1) usually semiprocumbent, with flattened bladelike apex, with or without distinct posterior accessory cusp. Second lower premolar (p2) taller than p3; lower milk premolar (dp3) trigonid incomplete (bicuspid). Hypoconid labially salient on m3; hypoconulid twinned with entoconid on m1–m3; entoconid much taller than hypoconulid on m1–m3. DISTRIBUTION: Species of Marmosa collectively range from the Mexican state of Tamaulipas southward throughout most of Central and tropical South America to Bolivia, Paraguay, and northern Argentina (Hall, 1981; Creighton and Gardner, 2008b; Gardner and Creighton, 2008b). Although most species inhabit lowland rainforests, a few are restricted to dry habitats (e.g., M. xerophila; Handley and Gordon, 1979) and some species of the subgenus Micoureus occur in montane rainforest at elevations in excess of 2000 m (e.g., M. mapiriensis sensu Tate, 1933: 76). REMARKS: The monophyly of Marmosa (including Micoureus) is supported by sequence data from five genes analyzed sepa- rately (figs. 28–32), in tandem (fig. 33), and in combination with nonmolecular characters (figs. 35, 36); generic monophyly is also supported by a uniquely shared insertion at the BRCA1 locus (fig. 31). Only a single morphological character, the possession of a rostral process of the premaxillae, optimizes as an unambiguous generic synapomorphy (appendix 5), but even this weak phenotypic evidence is compromised by the absence of a rostral process in M. xerophila, a species that we did not score for this study. No published phylogenetic analysis supports the reciprocal monophyly of Marmosa and Micoureus, both of which have been treated as valid genera by recent authors (e.g., Gardner, 2005; Creighton and Gardner, 2008b; Gardner and Creighton, 2008b). Instead, species of Micoureus have consistently been recovered as nested within a paraphyletic group of Marmosa species (Kirsch and Palma, 1995; Voss and Jansa, 2003; Jansa and Voss, 2005; Steiner et al., 2005; Jansa et al., 2006; Gruber et al., 2007). Obviously, there are several alternative taxonomic solutions to this problem. One solution would be to treat Micoureus as a junior synonym of Marmosa without recognizing any subgenera of the latter. Another would be to recognize Micoureus as a subgenus of Marmosa and to name new subgenera for other monophyletic clusters of Marmosa species. A third would be to recognize Micoureus as a genus and to describe new genera as needed to make Marmosa monophyletic. Unfortunately, the first option would result in the loss of a useful name (Micoureus, see below), whereas the second and third options are not currently workable because many species of Marmosa have not been included in any phylogenetic analysis, and their relationships are correspondingly obscure. Our interim solution is to move the currently intractable problem of paraphyly from the generic to the subgeneric level. Although taxonomic rank is biologically arbitrary, it affects binomial usage, which should be conformable with phylogenetic relationships insofar as these are known. In effect, because the use of generic names is obligatory under the current Linnaean system, it is crucial that genera be monophyletic.
2009 VOSS AND JANSA: DIDELPHID MARSUPIALS 105 The monophyly of Micoureus has been supported in every sequencing study to date that has included two or more exemplar species (e.g., Patton et al., 1996; Voss and Jansa, 2003; this study), and it may often be appropriate to indicate this fact in contradistinction to the paraphyly of the subgenus Marmosa. Where appropriate, this can be achieved using double quotes for the latter, as for the species Marmosa (‘‘Marmosa’’) lepida as contrasted with Marmosa (Micoureus) demerarae. Predictably, the subgeneric classification of Marmosa will be refined as future studies based on denser taxon sampling yield increasingly resolved estimates of relationships within this speciose group. Most of the species herein referred to Marmosa have not been revised since Tate (1933), and some currently recognized synonymies are the result of uncritical lumping by subsequent authors (e.g., Hershkovitz, 1951; Cabrera, 1958). Recent analyses of both mtDNA sequence data (e.g., by Patton et al., 2000; Patton and Costa, 2003) and morphological characters (Rossi, 2005) suggest that several nominal taxa currently listed as synonyms (e.g., of M. demerarae, M. murina, and M. robinsoni) are probably valid species. Therefore, significant changes to the species-level taxonomy of Marmosa should be expected soon. Monodelphis Burnett, 1830 Figure 42 CONTENTS: adusta Thomas, 1897 (including melanops Goldman, 1912); americana Müller, 1776 (including brasiliensis Erxleben, 1777; brasiliensis Daudin, 1802; trilineata Lund, 1840; and tristriata Illiger, 1815); brevicaudata Erxleben, 1777 (including brachyuros Schreber, 1777; dorsalis J.A. Allen, 1904; hunteri Waterhouse, 1841; orinoci Thomas, 1899; sebae Gray, 1827; surinamensis Zimmermann, 1780; touan Bechstein, 1800; touan Shaw, 1800; touan Daudin, 1802; and tricolor E. Geoffroy, 1803); dimidiata Wagner, 1847 (including fosteri Thomas, 1924); domestica Wagner, 1842 (including concolor Gervais, 1856); emiliae Thomas, 1912; glirina Wagner, 1842; handleyi Solari, 2007; iheringi Thomas, 1888; kunsi Pine, 1975; maraxina Thomas, 1923; osgoodi Doutt, 1938; palliolata Osgood, 1914; peruviana Osgood, 1913; reigi Lew and Pérez- Hernández, 2004; ronaldi Solari, 2004; rubida Thomas, 1899; scalops Thomas, 1888; sorex Hensel, 1872 (including henseli Thomas, 1888; itatiayae Miranda-Ribeiro, 1936; lundi Matschie, 1916; and paulensis Vieira, 1950); theresa Thomas, 1921; umbristriatus Miranda-Ribeiro, 1936; and unistriatus Wagner, 1842. MORPHOLOGICAL DESCRIPTION: Combined length of adult head and body ca. 70– 200 mm; adult weight ca. 15–150 g. Rhinarium with one ventrolateral groove on each side of median sulcus; dark circumocular mask absent; pale supraocular spot absent; dark midrostral stripe absent; throat gland present in adult males of most species but possibly absent in some (e.g., M. theresa). Dorsal pelage coloration highly variable, but dorsal hair bases always dark gray; dorsal guard hairs short and inconspicuous; ventral fur self-colored or gray based, highly variable in surface pigmentation. Manus mesaxonic (dIII . dIV); manual claws very long, extending well beyond fleshy apical pads of digits; dermatoglyph-bearing manual plantar pads present, but pads small and dermatoglyphs sometimes indistinct; central palmar epithelium smooth or sparsely tuberculate; carpal tubercles absent in both sexes. Pedal digits unwebbed; pedal digit III longer than digit IV; plantar surface of heel naked. Pouch absent; mammae 4–1–4 5 9 (all abdominal-inguinal; e.g., in M. brevicaudata) to 13–1–13 5 27 (including pectoral teats; e.g., in M. sorex); cloaca present. Tail much shorter than combined length of head and body; thick but muscular, not incrassate; tail conspicuously furred at base to about the same extent dorsally as ventrally (e.g., in M. emiliae), or caudal fur extends farther dorsally than ventrally (e.g., M. brevicaudata), or tail base unfurred (e.g., M. peruviana); unfurred caudal surfaces covered with macroscopic bristlelike hairs, not naked-appearing; caudal scales often inapparent but always in annular series; relationship between caudal scales and hairs usually obscure, but subequal hairs usually arranged in triplets; ventral caudal surface not modified for prehension. Premaxillary rostral process absent. Nasals long, extending anteriorly beyond I1 (con-
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PHYLOGENETIC RELATIONSHIPS AND CLAS
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CONTENTS Abstract .................
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ABSTRACT This report summarizes a d
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