Caluromysiops Sanborn, 1951

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 : 95-97

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Caluromysiops Sanborn, 1951
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Caluromysiops Sanborn, 1951   Figure 39

CONTENTS: irrupta Sanborn, 1951   .

MORPHOLOGICAL DESCRIPTION: Combined length of adult head and body probably ca. 250–300 mm ( Izor and Pine, 1987); adult weight probably ca. 300–500 g. Rhinarium with two ventrolateral grooves on each side of median sulcus; fur of head uniformly pale, without any marking (dark circumocular mask, supraocular spots, and midrostral stripes absent); throat gland absent. Dorsal pelage pale overall but prominently marked by paired blackish stripes extending from forelimbs to shoulders and thence posteriorly as narrowing parallel bands to rump; dorsal underfur dark (apparently grayish but discolored with age in all examined specimens); dorsal guard hairs short; ventral fur variously colored (gray-based buffy in some specimens, self-buffy in others). Manual digit IV longer than other manual digits; manual claws longer than fleshy apical pads of digits; dermatoglyph-bearing manual plantar pads present; central palmar epithelium smooth; carpal tubercles absent. Pedal digits unwebbed; dIV longer than other pedal digits; plantar surface of heel usually naked. Pouch said to be present ( Izor and Pine, 1987) but morphological details unknown; mammary formula unknown; cloaca present. Tail longer than combined length of head and body, slender and muscular (not incrassate); densely covered with body fur from base almost to tip except along ventral midline and posterolaterally; posterolateral caudal scales in spiral series, each scale with three subequal bristlelike hairs emerging from distal margin; naked ventral surface modified for prehension with raised tubercles near base, and apical pad bearing dermatoglyphs.

Premaxillary rostral process absent. Nasals long, extending anteriorly above I1 (conceal- ing nasal orifice from dorsal view), and conspicuously widened posteriorly near maxillary-frontal suture. Maxillary turbinals elaborately branched. One or two lacrimal foramina exposed on each side on or near anterior orbital margin. Large flattened, triangular postorbital processes of frontals present, continuous with supraorbital crests. Left and right frontals and parietals coossified in most adult specimens (median sutures incomplete or obliterated). Parietal and alisphenoid in contact on lateral braincase (no frontal-squamosal contact). Sagittal crest present, prominently developed on parietals and extending onto frontals in most adult specimens. Petrosal not laterally exposed through fenestra in parietal-squamosal suture (fenestra absent). Parietal-mastoid contact present (interparietal does not contact squamosal).

Maxillopalatine, palatine, and maxillary fenestrae absent (palate completely ossified); posterolateral palatal foramina small, not extending anteriorly between M4 protocones; posterior palatal morphology conforms to Caluromys   morphotype (without strongly developed lateral corners, the choanae unconstricted behind). Maxillary and alisphenoid widely separated by palatine on floor of orbit. Transverse canal foramen absent. Alisphenoid tympanic process smoothly globular, apparently always with posteromedial lamina enclosing extracranial course of mandibular nerve (secondary foramen ovale present), and extending posteriorly to contact or closely approximate rostral tympanic process of petrosal. Anterior limb of ectotympanic indirectly suspended from basicranium (by malleus). Stapes usually columellar and imperforate (rarely microperforate). Fenestra cochleae usually concealed in sinus formed by rostral and caudal tympanic processes of petrosal (but not in USNM 397626, possibly due to pathology or postmortem damage). Paroccipital process small, 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; angular process obtuse, weakly inflected.

Unworn crowns of I2–I5 asymmetrical (‘‘incisiform’’), with longer anterior than posterior cutting edges. Upper canine (C1) alveolus contained entirely within maxillary bone; C1 simple (without accessory cusps), and very large in adult specimens. First upper premolar (P1) absent or minute and vestigial; second upper premolar (P2) much taller than P3; P3 with both anterior and posterior cutting edges; upper milk premolar (dP3) large and molariform. Molars not carnassialized (postmetacristae subequal to postprotocristae); relative widths M1, M2. M3. M4; centrocrista straight (uninflected) on M1–M3; ectoflexus absent on all upper molars; 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) much taller than p3; lower milk premolar (dp3) large and nonvestigial, but paraconid not well developed (trigonid incomplete). Hypoconid labially salient on m3; hypoconulid not twinned with entoconid on any lower molar; entoconid much taller than hypoconulid on m1–m3.

DISTRIBUTION: Caluromysiops   is currently known from just seven localities in the rainforested Amazonian lowlands of southeastern Colombia, eastern Peru and western Brazil ( Emmons, 2008).

REMARKS: Various authors (e.g., Cabrera, 1958; Simpson, 1972; Izor and Pine, 1987) have questioned whether it is useful to separate Caluromysiops   from Caluromys   , but none explicitly considered the suite of trenchant morphological characters that distinguish these taxa. Among other features, Caluromysiops   differs from Caluromys   by its lack of a circumocular mask and dark midrostral stripe, presence of dark scapular stripes, shorter tail (table 5), absence of a premaxillary rostral process, co-ossified frontals, presence of a well-developed sagittal crest, presence of a secondary foramen ovale, globular (versus conical) alisphenoid bullae, columelliform stapes, linear centrocrista, and untwinned hypoconulid. Although there is no cladistic problem with combining these taxa under a single generic name, maintaining current binomial usage is likewise unobjectionable and serves to separate the monophyletic cluster of species currently known as Caluromys   from its long-branched sister taxon.