phylogenetic relationships and classification of didelphid marsupials ...

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112 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 322 combined length of head and body, slender and muscular (not incrassate), unfurred except at base; naked caudal integument bicolored basally (brownish or grayish dorsally, paler ventrally), gradually becoming all pale distally; caudal scales in both annular and spiral series (neither pattern predominating), each scale with three subequal bristlelike hairs emerging from distal margin; ventral caudal surface not externally modified for prehension. Premaxillary rostral process absent. Nasals long, extending anteriorly above or beyond I1 (concealing nasal orifice from dorsal view), and conspicuously widened posteriorly near maxillary-frontal suture. Maxillary turbinals elaborately branched. Two lacrimal foramina laterally exposed on each side on or just anterior to orbital margin. Interorbital region very broad, with distinctly beaded supraorbital margins; postorbital processes absent. Left and right frontals and parietals separated by persistent median sutures. Frontal and squamosal in contact on lateral braincase (no parietal-alisphenoid contact). Sagittal crest absent or weakly developed just anterior to occiput. Petrosal not exposed laterally through fenestra in parietal-squamosal suture (fenestra absent). Parietal-mastoid contact normally present (interparietal usually does not contact squamosal). Maxillopalatine fenestrae present; palatine and maxillary fenestrae absent; posterolateral palatal foramina small, not extending anteriorly between M4 protocones; posterior palatal morphology conforms to Didelphis morphotype (with well-developed lateral corners, the choanae constricted behind). Maxillary and alisphenoid usually not in contact on floor of orbit (separated by palatine in most examined specimens). Transverse canal foramen present. Alisphenoid tympanic process laterally compressed (not globular), with anteromedial process enclosing extracranial course of mandibular nerve (secondary foramen ovale present), and not in contact with rostral tympanic process of petrosal. Anterior limb of ectotympanic suspended directly from basicranium. Stapes triangular with large obturator foramen. Fenestra cochleae usually exposed, not or incompletely concealed by rostral and caudal tympanic processes of petrosal. Paroccipital process large, erect, projecting ventrally (not adnate to petrosal). Dorsal margin of foramen magnum bordered by exoccipitals only, incisura occipitalis absent. Two mental foramina present on lateral surface of each hemimandible; 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. 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 highly carnassialized (postmetacristae much longer than postprotocristae); relative widths M1 , M2 , M3 . M4 or M1 , M2 , M3 , M4; centrocrista strongly inflected labially on M1–M3; ectoflexus usually shallow on M1 and M2 but distinct on M3; anterolabial cingulum and preprotocrista usually discontinuous (anterior cingulum usually incomplete) 28 on M3; postprotocrista without carnassial notch. Third upper premolar (P3) and M4 erupt simultaneously. Lower incisors (i1–i4) with distinct lingual cusps. Lower canine (c1) procumbent, with flattened bladelike anterior margin, but usually without a distinct posterior accessory cusp. Second lower premolar (p2) taller than p3; lower milk premolar (dp3) trigonid complete (tricuspid). Hypoconid labially salient on m3; hypoconulid twinned with entoconid on m1–m3; entoconid much taller than hypoconulid on m1–m3. DISTRIBUTION: Metachirus is widely distributed in humid lowland and lower montane forests (usually below 2000 m) from Chiapas, Mexico (Medellín et al., 1992) to northern Argentina (Flores et al., 2007). Published distribution maps (e.g., Reid, 28 Because this character is normally quite constant within species, it is noteworthy that one specimen from Paracou, French Guiana (AMNH 266451), has a complete anterior cingulum whereas others from the same locality (e.g., AMNH 267362) have an incomplete anterior cingulum.
2009 VOSS AND JANSA: DIDELPHID MARSUPIALS 113 1997; Gardner and Dagosto, 2008) indicate several range disjunctions, but some of these may be artifacts of inadequate collecting effort in suitable habitats. REMARKS: Although only a single species of Metachirus is currently regarded as valid, recent mtDNA sequencing studies have revealed deep molecular divergence (.10% at the mitochondrial cytochrome b locus; Patton et al., 2000; Patton and Costa, 2003) among supposedly conspecific geographic populations, and it seems likely that several of the names currently listed as junior synonyms of M. nudicaudatus will be resurrected as valid species by future revisionary studies. Tribe Didelphini Gray, 1821 CONTENTS: Chironectes, Didelphis, Lutreolina, Philander, and {Thylophorops. DIAGNOSIS: Members of the tribe Didelphini differ from all other members of the subfamily Didelphinae by their possession of a well-developed pouch, black-and-white marked tail, nasal tips that do not extend above I1, co-ossified frontals, well-developed sagittal crest, ectotympanic suspension via the malleus only, delayed eruption of M4, and lower incisors without a distinct lingual cusp. REMARKS: The monophyly of Didelphini is strongly supported by most phylogenetic analyses published to date (e.g., Kirsch and Palma, 1995; Kirsch et al., 1997; Jansa and Voss, 2000, 2005; Voss and Jansa, 2003, this report; Steiner et al., 2005; Jansa et al., 2006; Gruber et al., 2007). The only exceptions appear to be primitive parsimony (‘‘Wagner’’) trees, unaccompanied by support statistics, that were based largely on dental characters (e.g., Reig et al., 1987: figs. 64–67). All of the diagnostic morphological features listed above, together with several other craniodental and karyotypic traits, optimize as unambiguous tribal synapomorphies (appendix 5). The monophyly of Didelphini is additionally supported by a uniquely shared deletion at the DMP1 locus (fig. 29), and by two uniquely shared deletions at the BRCA1 locus (fig. 31). Chironectes Illiger, 1811 Figure 45 CONTENTS: minimus Zimmermann, 1780 (including argyrodytes Dickey, 1928; bres- slaui Pohle, 1927; cayennensis Turton, 1800; guianensis Kerr, 1792; gujanensis Link, 1795; langsdorffi Boitard, 1845; palmata Daudin, 1802; panamensis Goldman, 1914; paraguensis Kerr, 1792; sarcovienna Shaw, 1800; variegatus Olfers, 1818; and yapock Desmarest, 1820). MORPHOLOGICAL DESCRIPTION: Combined length of adult head and body ca. 250– 320 mm; adult weight ca. 510–790 g. Rhinarium with one ventrolateral groove on each side of median sulcus; dark circumocular mask present, continuous with dark coronal fur (the whole top of the head except for an indistinct pale bar over each eye is blackish); pale supraocular spot absent; dark midrostral stripe absent; throat gland absent. Dorsal pelage pale silvery gray with blackish transverse bars connected by blackish middorsal stripe (when fresh; old museum skins become brownish or reddish with age); dorsal underfur pale gray; dorsal guard hairs short; ventral fur self-white. Manus mesaxonic (dIII .dIV); manual claws shorter than fleshy apical pads of digits; dermatoglyph-bearing manual plantar pads absent (plantar epithelium uniformly and very densely covered with minutely denticulate tubercles among which are scattered at regular intervals many smooth, hemispherical papillae); large, fleshy carpal tubercle supported internally by pisiform present in both sexes. Pedal digits webbed from base to terminal phalanges; dIV longer than other pedal digits; plantar surface of heel naked. Pouch present, opening posteriorly; mammae 2–1–2 5 5; cloaca absent (urogenital and rectal openings widely separated by furred skin). Tail longer than combined length of head and body, thick and muscular (not incrassate); body fur extends onto basal one-sixth or less of tail, to about the same extent dorsally as ventrally; naked caudal integument (beyond furry base) blackish with abruptly whitish tip (rarely all blackish); caudal scales in spiral series, each dorsal scale usually with three subequal bristlelike hairs emerging from distal margin (ventral scales often have 4–5 hairs each); ventral caudal surface not externally modified for prehension. Premaxillary rostral process absent. Nasals short, not extending anteriorly above I1 (exposing nasal orifice in dorsal view), and
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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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