Lutreolina Thomas, 1910

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 : 118-121

Lutreolina Thomas, 1910 Figure 47

CONTENTS: crassicaudata Desmarest, 1804 (including crassicaudis Olfers, 1818; bonaria Thomas, 1923; ferruginea Larrañaga, 1923; lutrilla Thomas, 1923; macroura Desmoulins, 1824; paranalis Thomas, 1923; travassosi Mirando-Ribeiro, 1936; and turneri Günther, 1879).

MORPHOLOGICAL DESCRIPTION: Combined length of adult head and body ca. 240– 345 mm; adult weight ca. 300–800 g). Rhinarium with one ventrolateral groove on each side of median sulcus; head entirely pale and unmarked (dark circumocular mask, pale supraocular spots, and dark midrostral stripe absent); throat gland absent. Dorsal pelage unpatterned, usually some shade of yellowish brown with grayish hair bases; dorsal guard hairs short and inconspicuous; ventral fur gray based or self-buffy. Manus mesaxonic (dIII. dIV); manual claws much longer than fleshy apical pads of digits; dermatoglyphbearing manual plantar pads present; central palmar epithelium more or less smooth; carpal tubercles absent. Pedal digits unwebbed; dIII longer than other pedal digits; plantar surface of heel naked. Pouch present, opening posteriorly; mammae 4–1–4 5 9 to 5–1–5 5 11; cloaca present. Tail usually slightly shorter than combined length of head and body, thicker than in other large opossums but muscular, not incrassate; furred to about the same extent dorsally and ventrally for basal one-third to one-half; naked caudal integument blackish proximally but abruptly whitish near tail tip; caudal scales in spiral series, each scale usually with four or five subequal bristlelike hairs emerging from distal margin; ventral caudal surface not externally modified for prehension.

Premaxillary rostral process absent. Nasals short, not extending anteriorly above I1 (exposing nasal orifice in dorsal view), and widened posteriorly near maxillary-frontal suture. Maxillary turbinals elaborately branched. Lacrimal foramina two on each side, exposed laterally on orbital margin or on face just anterior to orbit. Short, blunt, hornlike postorbital processes usually present in large adult specimens. Left and right frontals co-ossified (midfrontal suture incomplete or absent), but left and right parietals separated by persistent midparietal suture. Parietal and alisphenoid in contact on lateral braincase (no frontal-squamosal contact). Sagittal crest present, well developed on parietals and extending anteriorly onto frontals. Petrosal not laterally exposed through fenestra in squamosal-parietal suture (fenestra absent). Parietal-mastoid contact absent (interparietal narrowly contacts squamosal).

Maxillopalatine and palatine fenestrae present; maxillary fenestrae absent; posterolateral palatal foramina not extending anteriorly between M4 protocones; posterior palatal morphology conforming to Didelphis morphotype (with well-developed lateral corners, the choanae abruptly constricted behind). Maxillary and alisphenoid in contact (overlying palatine) on floor of orbit. Trans- verse canal foramen present. Alisphenoid tympanic process small and usually rounded (somewhat more inflated than in Chironectes or Didelphis ), with broad lamina enclosing extracranial course of mandibular nerve (secondary foramen ovale present), and not in contact with rostral tympanic process of petrosal. Anterior limb of ectotympanic suspended indirectly from braincase (by malleus). Stapes triangular with large obturator foramen; fenestra cochleae exposed (not enclosed by bony laminae). Paroccipital process large, erect, directed posteroventrally. Dorsal margin of foramen magnum bordered by exoccipitals only, incisura occipitalis absent.

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; third upper premolar (P3) taller than P2; P3 with posterior cutting edge only; upper milk premolar (dP3) large and molariform. Upper molars highly carnassialized (postmetacristae conspicuously longer than postprotocristae); relative widths M1, M2, M3, M4; centrocrista only weakly inflected labially on M1–M3; ectoflexus usually distinct only on M3; anterolabial cingulum and preprotocrista discontinuous (anterior cingulum incomplete) on M3; postprotocrista with carnassial notch. Last upper tooth to erupt is M4.

Lower incisors (i1–i4) without 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) large and molariform with complete (tricuspid) trigonid. Hypoconid lingual to protoconid (not labially salient) on m3; hypoconulid twinned with entoconid on m1– m3; entoconid taller than hypoconulid on m1 and m2, but sometimes subequal in height to hypoconulid on m3.

DISTRIBUTION: The known distribution of Lutreolina consists of two disjunct regions of nonforest vegetation in South America ( Stein and Patton, 2008b). Specimens traditionally referred to the subspecies L. crassicaudata turneri are from widely scattered localities in the savanna lowlands (below 900 m) in eastern Colombia and central Venezuela, and from the isolated but adjacent savannas of southern Venezuela and northern Guyana ( Voss, 1991: 91); although specimens of this form are currently unknown from Surinam and French Guiana, they could be expected to occur in the as yet poorly surveyed coastal savannas of either (or both) countries and in the adjacent Brazilian state of Amapá. Southern South American specimens (representing several nominal taxa in addition to the nominotypical subspecies L. c. crassicaudata ) are much more commonly collected in a wide range of tropical, subtropical, and temperate habitats in Paraguay, Uruguay, eastern Bolivia, southern Brazil, and northern Argentina ( Flores et al., 2007; Stein and Patton, 2008b).

REMARKS: Although several morphologically diagnosed subspecies of Lutreolina have been treated as valid by authors (e.g., Thomas, 1923; Ximénez, 1967; Graipel et al., 1996; Stein and Patton, 2008b), no published analysis of molecular variation has tested the implicit assumption that only a single species occurs across the vast range of South American landscapes from which specimens have been collected.