Tlacuatzin Voss and Jansa, 2003

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 : 108-110

Tlacuatzin Voss and Jansa, 2003 Figure 43

CONTENTS: canescens J.A. Allen, 1893 (including gaumeri Osgood, 1913; insularis Merriam, 1908; oaxacae Merriam, 1897; and sinaloae J.A. Allen, 1898).

MORPHOLOGICAL DESCRIPTION: Combined length of adult head and body ca. 110– 160 mm; adult weight ca. 30–70 g. Rhinarium with two ventrolateral grooves on each side of median sulcus; dark circumocular mask present; pale supraocular spot absent; dark midrostral stripe absent; throat gland absent. Dorsal pelage unpatterned, usually pale gray or grayish brown; dorsal underfur gray; dorsal guard hairs short and inconspicuous; ventral fur self-whitish, -cream, or -buffy. Manus paraxonic (dIII 5 dIV); manual claws about as long as fleshy apical pads of 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 of 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 of head and body, slender and muscular (not incrassate); body pelage present on basal 1/10 or less of 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), and 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 and right frontals and parietals separated by persistent median sutures. Parietal and 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 and alisphenoid not in contact on floor of orbit (separated by palatine). Transverse canal foramen present. Alisphenoid tympanic process smoothly globular, without anteromedial process or posteromedial lamina enclosing extracranial course of mandibular nerve (secondary foramen ovale absent), and not in contact with rostral tympanic process of squamosal. Anterior limb of ectotympanic directly suspend- ed from basicranium. Stapes usually subtriangular and microperforate or imperforate (rarely triangular with a large obturator foramen). Fenestra cochleae exposed, not concealed by rostral and caudal tympanic processes of petrosal. Paroccipital process of exoccipital small, rounded, 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 subequal 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) present, 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 longer than postprotocristae); relative widths usually M1, M2, M3, M4; centrocrista strongly inflected labially on M1–M3; ectoflexus usually absent on M1, shallow on M2, deep and distinct on M3; anterolabial cingulum continuous with preprotocrista (complete anterior cingulum present) 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). Second lower premolar (p2) taller than p3; lower milk premolar (dp3) with incomplete (usually bicuspid) trigonid. Hypoconid labially salient on m3; hypoconulid twinned with entoconid on m1–m3; entoconid taller than hypoconulid on m1– m2, usually subequal in height to hypoconulid on m3.

DISTRIBUTION: Tlacuatzin is apparently endemic to Mexico, where it occurs in tropical dry forests from Sonora southward (principally along the Pacific littoral and adjacent slopes of the coastal cordilleras) to Oaxaca and Chiapas; isolated populations also occur in the northern part of the Yucatan Peninsula and on the Tres Marías Islands ( Hall, 1981; Wilson, 1991; Reid, 1997; Zarza et al., 2003).