108 BULLETIN AMERICAN MUSEUM OF NATURAL HISTORY NO. 322 <strong>of</strong> Colombia <strong>and</strong> northern Ecuador (Solari, 2007), but no specimen-based records have yet been published from that region. REMARKS: The monophyly <strong>of</strong> Monodelphis vis-à-vis other Recent <strong>didelphid</strong>s is convincingly supported by 10 nonmolecular characters (appendix 5); by a uniquely shared <strong>and</strong> unreversed deletion at the BRCA1 locus (fig. 31); <strong>and</strong> by sequence data from five genes analyzed separately (figs. 28–32), together (fig. 33), <strong>and</strong> in combination with morphology <strong>and</strong> karyotypes (figs. 35, 36). Tlacuatzin Voss <strong>and</strong> Jansa, 2003 Figure 43 CONTENTS: canescens J.A. Allen, 1893 (including gaumeri Osgood, 1913; insularis Merriam, 1908; oaxacae Merriam, 1897; <strong>and</strong> sinaloae J.A. Allen, 1898). MORPHOLOGICAL DESCRIPTION: Combined length <strong>of</strong> adult head <strong>and</strong> body ca. 110– 160 mm; adult weight ca. 30–70 g. Rhinarium with two ventrolateral grooves on each side <strong>of</strong> median sulcus; dark circumocular mask present; pale supraocular spot absent; dark midrostral stripe absent; throat gl<strong>and</strong> absent. Dorsal pelage unpatterned, usually pale gray or grayish brown; dorsal underfur gray; dorsal guard hairs short <strong>and</strong> inconspicuous; ventral fur self-whitish, -cream, or -buffy. Manus paraxonic (dIII 5 dIV); manual claws about as long as fleshy apical pads <strong>of</strong> digits; dermatoglyph-bearing manual plantar pads present; central palmar epithelium sparsely tuberculate; adult males with well-developed lateral carpal tubercles but not medial carpal tubercles. Pedal digits unwebbed; dIV longer than other pedal digits; plantar surface <strong>of</strong> heel naked. Pouch absent; mammae 4–1–4 5 9 or 5–1–5 5 11, all abdominal-inguinal; cloaca present. Tail about as long as combined length <strong>of</strong> head <strong>and</strong> body, slender <strong>and</strong> muscular (not incrassate); body pelage present on basal 1/10 or less <strong>of</strong> tail; naked caudal integument uniformly grayish or faintly bicolored (darker dorsally than ventrally), occasionally parti-colored (with a whitish tip); caudal scales in annular series, each scale with three subequal bristlelike hairs emerging from distal margin; ventral caudal surface modified for prehension distally, with apical pad bearing dermatoglyphs. Premaxillary rostral process absent. Nasals long, extending anteriorly beyond I1 (concealing nasal orifice from dorsal view), <strong>and</strong> usually widened posteriorly near maxillaryfrontal suture. Maxillary turbinals elaborately branched. Lacrimal foramina visible in lateral view at or near anterior orbital margin, usually two on each side. Flattened, triangular postorbital processes well developed in fully adult specimens. Left <strong>and</strong> right frontals <strong>and</strong> parietals separated by persistent median sutures. Parietal <strong>and</strong> alisphenoid in contact on lateral braincase (no frontalsquamosal contact. Sagittal crest absent. Petrosal not exposed laterally through fenestra in parietal-squamosal suture (fenestra absent). Parietal-mastoid contact present (interparietal does not contact squamosal). Maxillopalatine fenestrae present; palatine fenestrae absent; maxillary fenestrae present, usually opposite M2, sometimes partially confluent with maxillopalatine openings; 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 <strong>and</strong> alisphenoid not in contact on floor <strong>of</strong> orbit (separated by palatine). Transverse canal foramen present. Alisphenoid tympanic process smoothly globular, without anteromedial process or posteromedial lamina enclosing extracranial course <strong>of</strong> m<strong>and</strong>ibular nerve (secondary foramen ovale absent), <strong>and</strong> not in contact with rostral tympanic process <strong>of</strong> squamosal. Anterior limb <strong>of</strong> ectotympanic directly suspended from basicranium. Stapes usually subtriangular <strong>and</strong> microperforate or imperforate (rarely triangular with a large obturator foramen). Fenestra cochleae exposed, not concealed by rostral <strong>and</strong> caudal tympanic processes <strong>of</strong> petrosal. Paroccipital process <strong>of</strong> exoccipital small, rounded, adnate to petrosal. Dorsal margin <strong>of</strong> foramen magnum bordered by supraoccipital <strong>and</strong> exoccipitals, incisura occipitalis present. Two mental foramina present on lateral surface <strong>of</strong> each hemim<strong>and</strong>ible; angular process acute <strong>and</strong> strongly inflected. Unworn crowns <strong>of</strong> I2–I5 symmetrically rhomboidal (‘‘premolariform’’), with subequal anterior <strong>and</strong> posterior cutting edges,
2009 VOSS AND JANSA: DIDELPHID MARSUPIALS 109 Fig. 43. Tlacuatzin canescens (based on primarily on USNM 511261, an adult female from Rancho Sapotito, Nayarit, Mexico; some dental details were reconstructed from USNM 125659, an adult male from Los Reyes, Michoacan, Mexico).
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