Hyladelphys Voss et al., 2001

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 : 97-100

Hyladelphys Voss et al., 2001 Figure 40

CONTENTS: kalinowskii Hershkovitz, 1992 .

MORPHOLOGICAL DESCRIPTION: Combined adult length of head and body ca. 75–95 mm; adult weight ca. 10–20 g. Rhinarium with two ventrolateral grooves on each side of median sulcus; dark circumocular mask

present, extending posteriorly from mystacial region to base of ear on each side of face; pale supraocular spot absent; dark midrostral stripe absent; throat gland absent. Dorsal pelage unpatterned reddish-brown with darkgray hair bases ; dorsal guard hairs short and inconspicuous; ventral fur self-white. Manus paraxonic (dIII 5 dIV); manual claws relatively large, strongly recurved, and slightly longer than fleshy apical pads of digits; dermatoglyph-bearing manual plantar pads present; central palmar epithelium smooth or sparsely tubercular; carpal tubercles absent. Pedal digits unwebbed; dIV longer than other pedal digits; plantar surface of heel naked. Pouch absent; mammae 2–0–2 5 4, all abdominal-inguinal; cloaca present. Tail much longer than combined length of head and body, slender and muscular (not incrassate), and apparently naked (without a conspicuously furred base) ; caudal scales in both annular and spiral series, each scale with three subequal bristle-like 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 above I1 (concealing most of nasal orifice from dorsal view), and conspicuously widened posteriorly near maxillary-frontal suture. Maxillary turbinals elaborately branched. Lacrimal foramina exposed laterally on or near anterior orbital margin, one or two on each side. Orbits very large; interorbital region strongly convergent anteriorly, with beaded dorsolateral margins; postorbital processes absent. 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 and maxillary fenestrae absent; posterolateral palatal foramina small, not extending anteriorly between M4 protocones. Posterior palatal morphology more Didelphis -like than Caluromys -like (with moderately well-developed posterolateral corners, the internal choanae distinctly constricted behind). Max- illary and alisphenoid bones not in contact on floor of orbit (widely separated by palatine). Transverse canal foramen present. Alisphenoid tympanic process smoothly globular, without anteromedial process or posteromedial lamina (secondary foramen ovale absent), 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 exposed, not concealed by rostral and caudal tympanic processes of petrosal. Paroccipital process small and adnate to petrosal. Dorsal margin of foramen magnum bordered by supraoccipital and exoccipitals, incisura occipitalis present.

One or two mental foramina present on lateral surface of each hemimandible; angular process acute and strongly inflected.

Unworn crowns of I2–I5 asymmetrical (‘‘incisiform’’), with much longer anterior than posterior cutting edges. 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 upper premolar (P2) much taller than P3; P3 with both anterior and posterior cutting edges; milk premolar (dP3) very small, vestigial, and lacking distinct occlusal features. Upper molars not strongly carnassialized (postmetacristae only slightly longer than postprotocristae); relative widths M1, M2, M3. M4; centrocrista weakly inflected labially on M1–M3; ectoflexus indistinct on M1, shallow on M2, 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) small, vestigial, and lacking distinct occlusal features. Hypoconid labially salient on m3; hypoconulid twinned with entoconid on m1– m3; entoconid taller than hypoconulid on m1–m3.

DISTRIBUTION: Currently known from few- er than a dozen specimens, Hyladelphys has been reported from just nine localities in the rainforested lowlands of eastern Peru, central Amazonian Brazil, southern Guyana, and French Guiana ( Astúa, 2007). Extrapolating from these scanty data is obviously problematic, but it would not be surprising to find this elusive taxon anywhere in Amazonia.

REMARKS: High levels of molecular divergence between sequenced specimens of Hyladelphys from French Guiana and Peru, together with geographic variation in morphological characters, suggest that additional species remain to be described in this genus ( Jansa and Voss, 2005).