Nephelomys, WEKSLER & PERCEQUILLO & VOSS, 2006

WEKSLER, MARCELO, PERCEQUILLO, ALEXANDRE REIS & VOSS, ROBERT S., 2006, Ten New Genera of Oryzomyine Rodents (Cricetidae: Sigmodontinae), American Museum Novitates 3537 (1), pp. 1-29 : 18-21

Nephelomys , new genus

TYPE SPECIES: Hesperomys albigularis Tomes, 1860 .

CONTENTS: albigularis Tomes, 1860 ; auriventer Thomas, 1899 ; caracolus Thomas, 1914 ; childi Thomas, 1895 (including oconnelli J.A. Allen, 1913); devius Bangs, 1902 ; keaysi J.A. Allen, 1900 (including obtusirostris J.A. Allen, 1900); levipes Thomas, 1902 ; maculiventer J.A. Allen, 1899 ; meridensis Thomas, 1894 ; moerex Thomas, 1914 ; nimbosus Anthony, 1926 ; pectoralis J.A. Allen, 1912 ; and pirrensis Goldman, 1913 .

DISTRIBUTION: In humid montane (‘‘cloud’’) forests between about 900 and 3500 m above sea level from Bolivia northward along the Andes and Central American cordilleras to Costa Rica, and eastward along the Caribbean coastal mountains to eastern Venezuela ( Percequillo, 2003).

MORPHOLOGICAL DIAGNOSIS: Dorsal pelage finely grizzled yellowish- to reddish-brown; ventral pelage abruptly paler (gray-based whitish) in some species, but not in others (which have gray-based ochraceous underparts); with irregular patches of self-whitish fur variably present on throat, chest, abdomen, and/or groin in some species. Ears small, not quite extending to eye when laid forward. Mystacial vibrissae usually extending posteriorly for several millimeters beyond caudal margins of pinnae when laid back, but superciliary vibrissae shorter (not extending beyond pinnae). Pes with conspicuous tufts of long ungual hairs at bases of claws on dII–dV; plantar surface smooth, without plantar squamae; hypothenar pad large and distinct; claw of dI extending to or just beyond middle of phalange 1 of dII; claw of dV extending to or just beyond first interphalangeal joint of dIV. Tail longer than combined length of head and body, weakly to distinctly bicolored (dark above, pale below).

Skull with long, stout rostrum flanked by relatively shallow to moderately deep zygomatic notches; interorbital region variable, hourglass-shaped with rounded supraorbital margins in some species (e.g., N. albigularis ) but anteriorly convergent with beaded interorbital margins in others (e.g., N. auriventer ); braincase rounded, usually with indistinct temporal crests in species having rounded supraorbital margins but with better-developed temporal crests in species having beaded supraorbital margins; lambdoidal and nuchal crests moderately developed in older adults. Posterior margin of zygomatic plate dorsal to M1 alveolus; jugal bone present but small in most species (the maxillary and squamosal zygomatic processes overlapping in lateral view but not in contact; N. auriventer , however, has a large jugal). Nasals usually not extending posteriorly beyond lacrimals; lacrimals sutured equally to maxillae and frontals in some species (e.g., N. albigularis ) or primarily to maxillae in others (e.g., N. moerex ). Frontosquamosal suture usually colinear with frontoparietal suture. Parietals with or without large lateral expansions (variable within and among species). Incisive foramina long (extending posteriorly to or between the alveoli of M1) and usually widest at midlength (e.g., in N. levipes ) or much shorter (never approaching the molar rows) and wider posteriorly than anteriorly (e.g., in N. moerex ). Posterolateral palatal pits usually large, complex, and recessed in deep fossae (but much reduced and inconspicuous in N. caracolus and N. nimbosus ); mesopterygoid fossa extending anteriorly between maxillae in most species, but often extending between toothrows in N. levipes ; bony roof of mesopterygoid fossa completely ossified or perforated by small sphenopalatine vacuities. Alisphenoid strut usually absent (buccinator– masticatory foramen and accessory oval foramen confluent) in most species, but strut usually present in N. moerex and variably present in others ( N. auriventer , N. levipes , and N. keaysi ). Stapedial foramen, squamosal– alisphenoid groove and sphenofrontal foramen present (5 carotid circulatory pattern 1 of Voss, 1988). Postglenoid foramen large and rounded; subsquamosal fenestra large and patent in most species but much narrower in N. auriventer . Periotic exposed posteromedially between ectotympanic and basioccipital but usually not extending anteriorly to carotid canal; mastoid completely ossified (e.g., in N. auriventer ) or usually fenestrated (e.g., in N. levipes ). Capsular process of lower incisor alveolus indistinct or absent; superior and inferior masseteric ridges converge anteriorly as open chevron below m1.

Labial and lingual flexi of M1 and M2 interpenetrating. First upper molar (M1) anterocone divided into labial and lingual conules by distinct anteromedian flexus; anteroloph well developed and fused with anterostyle on labial cingulum, separated from anterocone by persistent anteroflexus; protostyle absent; paracone connected by enamel bridge to posterior moiety of protocone. Second upper molar (M2) protoflexus present; mesoflexus present as single internal fossette. Third upper molar (M3) posteroloph present; hypoflexus shallow and transitory (disappearing with moderate wear). Labial accessory root of M1 absent.

First lower molar (m1) anteroconid usually without an anteromedian flexid (a shallow median crease visible on some newly erupted teeth is quickly obliterated by wear); anterolabial cingulum present on all lower molars; anterolophid usually distinct on unworn m1 but absent on m2 and m3; ectolophid present or absent on m1 and m2 (variable within and among species); mesolophid present and distinct on m1 and m2; m2 hypoflexid short. Accessory labial root of m1 usually present, accessory lingual root absent; m2 and m3 each with one large anterior root and one large posterior root.

Fifth lumbar (17th thoracicolumbar) vertebra usually with anapophysis. Hemal arch between second and third caudal vertebrae without posterior spinous process. Supratrochlear foramen of humerus present.

Stomach without extension of glandular epithelium into corpus. Macroscopic preputial glands absent. Distal bacular cartilage of glans penis large and trifid (with robust central

TABLE 3 Selected Morphological Comparisons Among New Genera from Clade B

digit); shelf of nonspinous tissue on crater rim does not conceal bacular mounds; dorsal papilla spineless; urethral processes without subapical lobules.

COMPARISONS: Phylogenetic analyses of nuclear gene sequences and morphology consistently recovered Nephelomys , represented by ‘‘ Oryzomys ’’ albigularis and ‘‘ O. ’’ levipes in Weksler (2003, 2006), as a member of clade B along with Euryoryzomys , Handleyomys , Hylaeamys , Oecomys , and Transandinomys (as in fig. 1 ). Within clade B, the relationships of Nephelomys were often unresolved, but some analytic permutations weakly supported a sister-group relationship with Transandinomys . Comparisons between Nephelomys and Transandinomys are summarized below, whereas comparisons among Nephelomys and other new taxa belonging to clade B are summarized in table 3.

Species of Nephelomys are larger-bodied than species of Transandinomys , a contrast that is apparent in most external dimensions. The adult hind foot (including claws), for example, averages about 32 mm or more in species of Nephelomys , whereas this dimension averages about 30 mm or less in Transandinomys (see measurements in Musser et al., 1998). In addition, species of Nephelomys have relatively shorter superciliary vibrissae, smaller pinnae, longer fifth pedal digits, and longer tails than Transandinomys (see the diagnoses of both taxa for ratios or landmark comparisons that document these differences).

The most conspicuous qualitative craniodental difference between Nephelomys and Transandinomys concerns the anterocone of M1, which is deeply divided into labial and lingual conules by a persistent anteromedian flexus in the former genus. By contrast, the anterocone of M1 is undivided and no trace of an anteromedian flexus is present in Transandinomys . The size difference between these genera indicated by external dimensions is also apparent in craniodental comparisons: length of the maxillary toothrow, for example, consistently averages.5.5 mm in species of Nephelomys , but this measurement averages,4.7 mm in species samples of Transandinomys . The accessory root(s) that are usually present on m 1 in Nephelomys are apparently never developed in Transandinomys .

Due to morphological variation among congeneric taxa (as noted above in this account and below in the account that follows), consistent differences between Nephelomys and Transandinomys are not apparent in any other characters that we have been able to score in all member species. However, the potentially diagnostic value of preputial morphology deserves future study. Among the material dissected by Voss and Linzey (1981), a single pair of large preputial glands was found in Transandinomys talamancae (represented by their Panamanian specimens of ‘‘ Oryzomys capito ’’), but no macroscopic preputial glands were detected in Nephelomys devius (represented by their specimens of ‘‘ Oryzomys albigularis ’’); unfortunately, no additional species from either genus were included in that study and none have been dissected by other investigators.

REMARKS: All of the taxa that we refer to Nephelomys were treated as synonyms or subspecies of ‘‘ Oryzomys ’’ albigularis by Hershkovitz (1944: 72) and Cabrera (1961: 380–383), but subsequent karyotypic and morphological research has shown that most of these are valid species ( Gardner and Patton, 1976; Patton et al., 1990; Aguilera et al., 1995; Márquez et al., 2000; Percequillo, 2003). Of the characters that Weksler (2006) identified as unambiguous synapomorphies of ‘‘ O. ’’ albigularis + ‘‘ O. ’’ levipes , only the divided anterocone of M1 seems to be exhibited consistently by other species of Nephelomys . Although no additional analytic results are currently available to support generic monophyly, we are not aware of any evidence that contradicts this hypothesis.

ETYMOLOGY: From nephelê (Greek for clouds or mist), in reference to the cloudforest habitat of these montane species.

Figures

Fig. 1. Phylogenetic relationships of oryzomyines based on a heuristic parsimony analysis of sequence data from the Interphotoreceptor Retinoid Binding Protein (IRBP, 1266 bp from exon 1) and 99 morphological characters (after Weksler, 2006: fig. 37). Numbers above and below branches represent jackknife support (.50%) and decay indices (.1), respectively. Vertical bars on the right-hand side of the figure indicate taxon membership in clades A–D. See Weksler (2006: 14–17) for methodological details.