Monodelphis Burnett, 1830

Voss, RS & Jansa, SA, 2009, Phylogenetic Relationships And Classification Of Didelphid Marsupials, An Extant Radiation Of New World Metatherian Mammals, Bulletin of the American Museum of Natural History 2009 (322), pp. 1-177 : 105-108

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Monodelphis Burnett, 1830


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- cealing nasal orifice from dorsal view), and conspicuously widened posteriorly near maxillary-frontal suture. Maxillary turbinals (viewed through the nasal orifice) simple or sparsely ornamented scrolls, not elaborately branched. Lacrimal foramina (usually two on each side) prominently exposed on orbital margin or on face anterior to orbit. Orbits small, interorbital region more or less parallel sided (usually without conspicuous constrictions); supraorbital margins smoothly round- ed, without beads or distinct postorbital processes (but blunt, indistinct processes occasionally developed in large specimens of some species; e.g., M. emiliae   ). Parietal and alisphenoid in contact on lateral braincase (no frontal-squamosal contact). Sagittal crest absent (e.g., in M. theresa   ) or small (usually not extending to frontals; e.g., in M. brevicaudata   ). Petrosal not exposed laterally through fenestra in parietal-squamosal suture (fenestra absent). Parietal-mastoid contact usually present (interparietal seldom contacts squamosal).

Maxillopalatine fenestrae present; palatine fenestrae usually absent; maxillary fenestrae absent; posterolateral palatal foramina small, not extending anteriorly between M4 protocones; posterior palatal morphology conforms to Didelphis   morphotype (with moderately well-developed lateral corners, the choanae somewhat constricted behind). Maxillary and alisphenoid in contact on floor of orbit (not separated by palatine). Transverse canal foramen present. Alisphenoid tympanic process smoothly globular; posteromedial lamina forming secondary foramen ovale present in some species (e.g., M. theresa   ) or lamina and secondary foramen ovale absent (e.g., in M. brevicaudata   ). Anterior limb of ectotympanic suspended directly from basicranium. Stapes triangular with large obturator foramen (e.g., in M. brevicaudata   ), or columellar and microperforate or imperforate (e.g., in M. peruviana   ). Fenestra cochleae exposed in most species, but fenestra concealed in sinus formed by rostral and caudal tympanic processes of petrosal in M. emiliae   . Paroccipital process small, rounded, and adnate to petrosal. Dorsal margin of foramen magnum bordered by supraoccipital and exoccipitals, incisura occipitalis present.

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 usually increasing in length (mesiodistal dimension) from I2 to I5. Upper canine (C1) alveolus in premaxillary-maxillary suture; C1 usually simple (without accessory cusps), but small posterior accessory cusp sometimes present (e.g., in M. peruviana   ). First upper premolar (P1) smaller than posterior premolars but well formed and not vestigial; third upper premolar (P3) taller than P2; P3 with posterior cutting edge only; upper milk premolar (dP3) large and molariform. Molars highly carnassialized (postmetacristae much longer than postprotocristae); relative widths consistently M1, M2, M3, M4; centrocrista strongly inflected labially on M1– M3; ectoflexus shallow on M1, deeper on M2, and consistently deep on M3; anterolabial cingulum and preprotocrista discontinuous (anterior cingulum incomplete) on M3. Last upper tooth to erupt is P 3 in some species (e.g., M. peruviana   ), or P3 and M4 erupt simultaneously (e.g., in M. brevicaudata   ).

Lower incisors (i1–i4) with distinct lingual cusps. Second lower premolar (p2) subequal in height to p3 (e.g., in M. brevicaudata   ), or p3 taller than p2 (e.g., in M. emiliae   ); lower milk premolar (dp3) trigonid usually complete (tricuspid). Hypoconid lingual to protoconid (not labially salient) on m3; hypoconulid twinned with entoconid on m1–m3; entoconid subequal to or smaller than hypoconulid on m1–m3.

DISTRIBUTION: Species of Monodelphis   occur in lowland and montane rain forests and dry forests from eastern Panama throughout most of tropical and subtropical South America to about 37 ° S in eastern Argentina (see range maps in Pine and Handley, 2008); recorded elevations range from sea level to at least 2500 m (on the eastern slopes of the tropical Andes). The apparent absence of Monodelphis   from the trans-Andean lowlands of western South America is noteworthy, but this is possibly an artifact of inadequate collecting; a representative of the M. adusta   complex is rumored to occur along the Pacific littoral of Colombia and northern Ecuador ( Solari, 2007), but no specimen-based records have yet been published from that region.

REMARKS: The monophyly of Monodelphis   vis-à-vis other Recent didelphids is convincingly supported by 10 nonmolecular characters (appendix 5); by a uniquely shared and unreversed deletion at the BRCA1 locus (fig. 31); and by sequence data from five genes analyzed separately (figs. 28–32), together (fig. 33), and in combination with morphology and karyotypes (figs. 35, 36).