Lestodelphys Tate, 1934

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 : 131-133

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Lestodelphys Tate, 1934


Lestodelphys Tate, 1934   Figure 51

CONTENTS: halli Thomas, 1921   .

MORPHOLOGICAL DESCRIPTION: Combined length of adult head and body probably ca. 120–160 mm; adult weight probably ca. 60– 100 g (very few reliably measured specimens accompanied by weights are available). Rhinarium with one ventrolateral groove on each side of median sulcus; dark circumocular mask present; pale supraocular spot absent; dark midrostral stripe absent; throat gland present in adult males. Dorsal pelage tricolored (distinctly darker middorsally than on flanks); dorsal underfur dark gray; dorsal guard hairs short and inconspicuous; ventral fur self-white from chin to anus. Manus mesaxonic (dIII. dIV); manual claws much longer than fleshy apical pads of digits; dermatoglyph-bearing manual plantar pads present; central palmar epithelium densely tuberculate; carpal tubercles absent. Pedal digits unwebbed; dIII longer than other pedal digits; plantar surface of heel coarsely furred. Pouch absent; mammae 8–1–8 5 17 or 9–1–9 5 19, of which the anteriormost teats are ‘‘pectoral’’; cloaca present. Tail shorter than combined length of head and body, incrassate, and unfurred except at base; caudal integument bicolored (dark above, distinctly paler below); tail scales difficult to distinguish but apparently in annular series; caudal hairs all subequal in length and thickness; ventral caudal surface not modified for prehension.

Premaxillary rostral process absent. Nasals long, extending anterior to I1 (concealing nasal orifice in dorsal view), and conspicuously widened posteriorly near premaxillarymaxillary suture. Maxillary turbinals elaborately branched. Two lacrimal foramina present on each side, exposed in lateral view anterior to orbital margin. Supraorbital margins smoothly rounded, without beads or crests; postorbital frontal processes usually absent (indistinct processes are occasionally developed in old adult males). Left and right frontals and parietals separated by persistent median sutures. Parietal and alisphenoid bones in contact on lateral surface of braincase (no frontal-squamosal contact). Sagittal crest usually absent but weakly developed along midparietal suture (not extending anteriorly to frontals) in some large specimens.31 Petrosal exposed through fenestra in parietal-squamosal suture in some individuals but not in others. Parietal-mastoid contact present (interparietal does not contact squamosal).

Maxillopalatine fenestrae present but sometimes quite small; palatine fenestrae variable but usually present ( Martin, 2005: fig. 2); maxillary fenestrae absent; posterolateral palatal foramina very long, usually extending anteriorly lingual to M4 protocones; posterior palatal morphology conforms to Didelphis   morphotype (with strongly produced posterolateral corners, the choanae constricted behind). Maxillary and alisphenoid not in contact (separated by palatine) on floor of orbit. Transverse canal foramen present. Alisphenoid tympanic process smoothly globular, with well-developed anteromedial process enclosing extracranial course of mandibular nerve (secondary foramen ovale present), and not contacting rostral tympanic process of petrosal. Anteri- or limb of ectotympanic directly suspended from basicranium. Stapes usually columelli-

31 Among the specimens we examined, a small sagittal crest is best developed in UWZM 22422.

form and microperforate or imperforate. Fenestra cochleae concealed in sinus formed by rostral and caudal tympanic processes of petrosal. Paroccipital process small, rounded, and adnate to petrosal. Dorsal margin of foramen magnum bordered by supraoccipital and exoccipitals, incisura occipitalis present.

Two mental foramina usually present on lateral surface of each hemimandible (three foramina are present unilaterally on two specimens examined); angular process acute and strongly inflected.

Unworn crowns of I2–I5 symmetrically rhomboidal (‘‘premolariform’’), with subequal anterior and posterior cutting edges, slightly 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; third upper premolar (P3) taller than P2; P3 with posterior cutting edge only; upper milk premolar (dP3) large and molariform. Molars strongly carnassialized (postmetacristae much longer than postprotocrista); relative widths M1, M2, M3, M4; centrocrista strongly inflected labially on M1–M3; ectoflexus shallow or absent on M1, consistently present and distinct on M2, consistently deep on M3; anterolabial cingulum and preprotocrista discontinuous (anterior cingulum incomplete) on M3; postprotocrista without carnassial notch. Last upper tooth to erupt is P3.

Lower incisors (i1–i4) with distinct lingual cusps. Lower canine (c1) erect, acutely pointed, and simple (without a posterior accessory cusp). Third lower premolar (p3) taller than p2; lower milk premolar (dp3) large, but trigonid incomplete (uni- or bicuspid). Hypoconid lingual to protoconid (not labially salient) on m3; hypoconulid twinned with entoconid on m1–m3; entoconid taller than hypoconulid on m1–m3.

DISTRIBUTION: Most known specimens of Lestodelphys   have been collected in semidesert shrubland and steppe habitats in Patagonian Argentina between 41 ° and 47 ° S latitude, but there are two outlying records from the Monte desert (between 32 ° and 38 ° S) that may represent a relictual population ( Sauthier et al., 2007); all reported elevations associated with collected specimens are less than 1000 m above sea level ( Birney et al., 1996; Martin, 2003). As noted by Flores et al. (2007), the distribution of Lestodelphys   extends further south than that of any other living marsupial.