Transandinomys bolivaris, J. A. Allen, 1901

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 : 25-26

MORPHOLOGICAL DIAGNOSIS: Dorsal pelage finely grizzled brownish (in T. bolivaris ) or tawny (in T. talamancae ); ventral pelage abruptly paler (superficially whitish), but ventral hairs uniformly gray-based over throat, chest, abdomen, and groin. Pinnae large, reaching eye when laid forward. Mystacial vibrissae long (extending posteriorly to or slightly beyond caudal margins of pinnae when laid back against cheeks in T. talamancae ) or very long (extending well behind pinnae in T. bolivaris ); superciliary vibrissae extending behind pinnae in both species (but much longer in T. bolivaris than in T. talamancae ). Pes with conspicuous tufts of long ungual hairs at bases of claws on dII– dV; plantar surface entirely smooth (in T. bolivaris ) or sparsely covered with indistinct squamae distal to thenar pad (in T. talamancae ); hypothenar pad present and distinct; claw of dI extending almost to middle of phalange 1 of dII; claw of dV extending almost to first interphalangeal joint of dIV. Tail about as long as or slightly longer than combined length of head and body; unicolored in T. bolivaris but often distinctly bicolored (dark above, pale below) in T. talamancae .

Skull with long, tapering rostrum flanked by moderately deep zygomatic notches; interorbital region anteriorly convergent, with beaded supraorbital margins; braincase rounded, with moderately well-developed temporal crests; lambdoidal and nuchal crests developed in older adults. Posterior margin of zygomatic plate usually dorsal to M1 alveolus. Jugal present but small (maxillary and squamosal zygomatic processes overlapping in lateral view but not in contact). Nasals not extending posteriorly beyond lacrimals; lacrimals equally sutured to maxillary and frontal bones. Frontosquamosal suture usually colinear with frontoparietal suture. Parietals with broad lateral expansions (in T. talamancae ) or lateral expansions reduced or absent (in T. bolivaris ). Incisive foramina short (not extending posteriorly between the alveoli of M1) and usually wider posteriorly than anteriorly (teardrop-shaped). Posterolateral palatal pits usually simple and recessed (if at all) in shallow fossae; mesopterygoid fossa usually not extending anteriorly between maxillae; bony roof of mesopterygoid fossa completely ossified or perforated by small sphenopalatine vacuities. Alisphenoid strut absent (buccinator–masticatory foramen and accessory oval foramen confluent). Stapedial foramen, squamosal–alisphenoid groove, and sphenofrontal foramen present (5 carotid circulatory pattern 1 of Voss, 1988). Postglenoid foramen large and rounded, subsquamosal fenestra usually large and patent. Periotic exposed posteromedially between ectotympanic and basioccipital but not extending anteriorly to carotid canal; mastoid usually unfenestrated in T. bolivaris but fenestrated in T. talamancae . Capsular process of lower incisor alveolus indistinct or absent; superior and inferior masseteric ridges converge anteriorly as open chevron below m1.

First upper molar (M1) anterocone not divided into labial and lingual conules (anteromedian flexus absent); anteroloph well developed, fused with anterostyle on labial cingulum, separated from anterocone by persistent anteroflexus; protostyle absent; paracone usually connected by enamel bridge to posterior end of protocone. Second upper molar (M2) protoflexus present; mesoflexus present as single internal fossette. Third upper molar (M3) posteroloph absent; hypoflexus shallow and transitory (usually disappearing with moderate wear). Labial accessory root of M1 absent.

First lower molar (m1) anteroconid without an anteromedian flexid; anterolabial cingulum present on all lower molars; anterolophid distinct on m1 but absent on m2 and m3; ectolophid often present on m1 and m2; mesolophid present on m1 and m2; m2 hypoflexid long and deep, almost bisecting tooth. Accessory labial and lingual roots absent on m1; m2 and m3 each with one large anterior root and one large posterior root.

Fifth lumbar (17th thoracicolumbar) vertebra with well-developed 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. Distal bacular cartilage of glans penis large and trifid (with robust central digit); shelf of nonspinous tissue on crater rim does not conceal bacular mounds; dorsal papilla spineless; urethral processes without subapical lobules.

COMPARISONS: Weksler (2003, 2006) consistently recovered Transandinomys (represent- ed by ‘‘ O. ’’ talamancae ) as a member of clade B together with Euryoryzomys , Handleyomys , Hylaeamys , Nephelomys , and Oecomys (as in fig. 1 ). Within clade B, Transandinomys was variously recovered by different analytic permutations as the sister taxon of Euryoryzomys , of Nephelomys , or of Handleyomys intectus + Nephelomys . Comparisons of Transandinomys with Euryoryzomys , Hylaeamys , and Nephelomys have already been provided in the accounts for those genera, salient aspects of which are summarized in table 3. The morphology of Handleyomys intectus (redescribed by Voss et al., 2002) is sufficiently distinctive that direct comparisons seem unnecessary in this context.

REMARKS: Although Transandinomys bolivaris and T. talamancae are phenetically similar (as remarked by Musser et al., 1998: 323), no analytic results are currently available to support the monophyly of this genus. The only unambiguously derived trait that appears to be uniquely shared by these species is their possession of unusually long supraorbital vibrissae, a character that was not scored for phylogenetic analysis by Weksler (2006).

ETYMOLOGY: For the trans-Andean distribution of these 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.