Thomasomys cinereus Voss, 1993

Pacheco, Víctor & Ruelas, Dennisse, 2023, Systematic Revision Of Thomasomys Cinereus (Rodentia: Cricetidae: Sigmodontinae) From Northern Peru And Southern Ecuador, With Descriptions Of Three New Species, Bulletin of the American Museum of Natural History 2023 (461), pp. 1-73 : 35-44

Thomasomys cinereus Voss, 1993 : part, Thomasomys sp. 2 Brito et al., 2019: 9.

HOLOTYPE: An adult female specimen housed in the Museo de Historia Natural de la Universidad Nacional Mayor de San Marcos ( MUSM 23758 ), collected by V. Pacheco on April 28, 2006 (original field number VPT 3149 ). The holotype is preserved as skin and skull in good condition.

PARATYPES: Four paratypes from the same locality, two females ( MUSM 23759, 23762) and two males ( MUSM 23760, 23761).

TYPE LOCALITY: Peru, Department of Piura, Province of Huancabamba, Pariamarca Alto ; 5.15867°S, 79.54901°W, 2990 m above sea level.

DIAGNOSIS: A medium-sized Thomasomys (table 3) that can be distinguished from its congeners by the following combination of characters: dorsal pelage long and soft, brownish with hair tips yellowish; mystacial vibrissae long, extending beyond posterior margin of pinnae; tail longer than head-and-body length, unicolored and without a white tip; thenar and hypothenar pads separated; plantar surface of hind foot pale; nasal relatively short, expanded anteriorly, and tapering posteriorly to the maxilla-frontal-lacrimal intersection or shorter; zygomatic notch shallow; incisive foramina long, extending posteriorly to the anterior margins of first molars, not between; palatal median process usually present (78%); Eustachian tube short and broad; stapedial process of bulla reduced; capsular process of lower incisors alveolus absent; M1 anteromedian flexus weak; M3 hypoflexus weak; and m1 anteromedian flexid weakly produced.

MORPHOLOGICAL DESCRIPTION: Thomasomys lojapiuranus is a medium-size Thomasomys (HBL = 107–146 mm) with long, soft, and dense dorsal fur (individual hairs about 14–16 mm). Dorsal pelage is brownish (Dark Drab, color 119B) with hairs slate colored at the base. Ventral pelage is gray whitish (Smoke Gray, color 45) or washed with pale brown, individual hairs slate colored basally. Dorsal and ventral pelage are moderately countershaded (figs. 8, 9). The ears are moderately long (EL = 18–26 mm) and paler. Postauricular patches of cream-colored fur are conspicuous. The mystacial vibrissae are long, extending behind the posterior margin of the pinnae by about half the pinnae length when laid back alongside the head. The supraorbital vibrissae are also relatively long, extending behind the posterior margins of pinnae when laid back alongside the head. The genal 1 vibrissae are absent. The tail is on average longer than the combined length of head and body (Tail% = 117), comparatively thick, mostly unicolored, and without a white tip. The metacarpals are pale brownish. Digit II of manus is larger than digit V. The hindfeet are moderately long (HFL = 28–32 mm) with metatarsal patch pale brownish, and dense ungual tufts. The plantar surface of the hind foot is pale. The thenar and hypothenar pads are separated by a distinct gap (fig. 10B). Digit I of the hind foot (hallux) is moderately long, its claw extending close or to the first interphalangeal joint of dII. Digit V of the hind foot is long, with the claw extending about half the length of phalanx 2 of dIV.

Cranium: The skull is moderately large (CIL = 29–32 mm) with a relatively long and moderately broad rostrum. The skull dorsal profile is slightly convex, never straight, with a small bump at the interorbital region level. A rostral tube is absent, and the gnathic process is small (figs. 12B, 15B). The nasals are short and tapering; the anterior half is expanded; the posterior margins are narrow, extending posteriorly to the maxilla-frontal-lacrimal intersection or shorter and barely beyond the premaxillae. The zygomatic notches are shallow (fig. 13B). The interorbital region is moderately broad and hourglass shaped with rounded margins, and the frontal sinus are relatively inflated. The interparietal is wide and moderately long anteroposteriorly, straplike in some specimens, but rhomboidal in others. The premaxillae are slightly produced anteriorly beyond the incisors (fig. 15B). The zygomatic arches converge anteriorly to a moderate degree. The zygomatic plates are moderately broad, subequal in breadth to the length of M1, and moderately sloped backward (fig. 15B). The zygomatic process of the maxilla and the zygomatic process of the squamosal are closely approximated (80%) or separated by a distinct gap (20%) (fig. 16B). The postglenoid foramen is small and placed anterior to a relatively larger subsquamosal fenestra. The tegmen tympani is robust and overlaps a distinct suspensory process of the squamosal. The carotid circulatory pattern is pattern 1 (sensu Voss, 1988): a stapedial foramen, a groove on the inner surface of the squamosal and the alisphenoid, and a sphenofrontal foramen are all present. In the medial wall of the orbit, the ethmoid foramen is placed dorsal to M2; the ethmoturbinals are moderate in size; the sphenopalatine foramen is bordered by the maxillary, ethmoid, and palatine bones; and the optic foramen is moderate in size and slightly posterior to M3. The paraoccipital process is small. The incisive foramina are long and extend posteriorly to the anterior margins of the first molars, not between, and are widest behind the premaxillary-maxillary suture; the posterior margins are rounded (fig. 17B). The mesopterygoid fossa is broad and expanded anteriorly, the roof is closed, and the sides are subparallel; the palatal median process is present (in 78% of examined specimens). The parapterygoid fossa is triangular, shallow, and without vacuities. The foramen ovale is moderate in size, the alisphenoid strut is present, and the middle lacerate foramen is narrow but conspicuous. The auditory bullae are small, flask shaped, and moderately inflated with short and broad Eustachian tubes; the stapedial process of bulla is reduced. The internal carotid canal is bounded by the basioccipital and the ectotympanic (auditory bulla), but not by the periotic. The basioccipital is moderately broad, the mastoid (the occipital exposure of the periotic) is either imperforate or has only a small fenestra. The lamina of the malleus is squarish and not deep, and the orbicular apophysis is elongated without a basal constriction (fig. 18B). The processus brevis of the incus is long, narrow, and delicate.

Teeth: The upper incisors are orthodont with orange enamel on their anterior surfaces. The upper molar rows are moderately long (4.8–5.5 mm). The upper molars are brachyodont and pentalophodont (sensu Hershkovitz, 1962) without interpenetration of the labial and lingual flexi; labial and lingual cingula are not developed; and accessory labial roots are absent. The procingulum of M1 is slightly narrower than the protocone-paracone cusp pair, and the anteromedian flexus is weak or coalesced. The anteroloph is conspicuous and the paraflexus is recurved. The paraloph is oriented transversally to the median mure, to the base of the mesoloph, or the mesoloph. The mesoloph is narrow and well developed and reaches the labial margin of the tooth. The metaflexus is slightly curved. The posteroloph is coalesced with the metacone. M2 exhibits a strong anteroloph with a recurved paraflexus; the mesoloph is narrow and complete, the metaflexus is comma shaped, and the posteroloph is coalesced with the metacone. M3 is smaller compared to M2; its paraflexus is conspicuous but the hypoflexus is reduced (fig. 19B).

On the lower molars, the main cuspids are conspicuous and slightly alternating. The first lower molar (m1) has a weak anteromedian flexid; the protolophid and anterolophid are short and quickly coalesced; the anterolabial and anterolingual cingula are poorly developed; the mesoflexid is narrow and recurved; the entoflexid is small or coalesced; the posteroflexid is narrow and almost straight; the hypoflexid is narrow and oriented perpendicularly; and the mesolophid is narrow but complete. On m2, the mesolophid is short and the anterolabial cingulum is small. The m3 has a subtriangular occlusal shape produced by the less developed entoconid; the mesoflexid and hypoflexid are conspicuous; and the posteroflexid is coalesced (fig. 19F).

Mandible: The coronoid process is long, narrow, falciform, and taller than the condylar process, producing a deep sigmoid notch. The angular process is well developed and on the same plane as or slightly anterior to the condylar process. The ventral border of the mandible is deeply concave. The capsular process of the lower incisor alveolus is absent (fig. 24).

Hyoid apparatus: Hyoid morphology like that described for Thomasomys cinereus (observation made only in one specimen).

Penis: Two fluid-preserved male specimens (MUSM 23760, 23761) were examined. The glans is medium size, subcylindrical, relatively long (4.48 mm), and narrow (2.28 mm) (fig. 20B). A dorsal groove is absent, and a ventral groove is exhibited as a shallow sulcus. The external surface of the glans is covered by small epidermal spines overall except along the crater rim. The spineless crater lip circumscribes the entire crater opening and is separated from the spinous epithelium by a thick fold. Distally, the glans is not divided on the lateral sides, but a shallow notch is present (fig. 20B). The medial bacular mound projects prominently from the crater lip and is thus visible externally; the lateral bacular mounds are much smaller than in Thomasomys cinereus , lack ornamentation, and are not visible externally. The tip of the medial bacular mound is broad and oriented vertically or slightly ventrally oriented. The urethral flaps are small, conical, deeply buried within the crater, and lack ornamentation. The dorsal papilla is small, conical, and lack spines or other ornamentation.

Palatal rugae: Two complete (diastemal) and five incomplete (interdental) transverse palatal ridges like in Thomasomys cinereus , except that the interdental ruga i4 extends to the palate midline and the interdental ruga i5 is nearly straight (fig. 21).

Stomach: The stomach corresponds to the unilocular-hemiglandular morphotype ( Carleton, 1973; Pacheco, 2003). The incisura angularis is shallow, and the bordering fold is thicker and crosses the lesser curvature of the stomach slightly anterior to the incisura angularis; the bordering fold also gently recurves to the left but not beyond the esophageal orifice (fig. 22B).

Gall bladder: Present.

Reproductive glands: Macroscopic preputial glands are absent.

Skeleton: The vertebral count is 7 cervical, 13 thoracic, 6 lumbar, 4 sacral, and 37 to 40 caudal vertebrae; and the same skeletons each have 13 pairs of ribs. The supratrochlear fenestra of humerus is usually absent (6 of 7 samples). The first caudal vertebra has chevron bones fused forming a closed arch, mostly without a spinous process (in 5 of 7 examined specimens). As described by Pacheco (2003), on the calcaneus, the trochlear process levels its posterior articular facet; and the peroneal process of the fifth metatarsal is moderately long but not extending to the proximal edge of the cuboid.

Karyotype: Unknown.

MEASUREMENTS OF HOLOTYPE: GSL, 33.1; CIL, 30.15; CML, 19.52; LOF, 10.5; LN, 12.03; RL, 11.28; LD, 8.94; LIF, 6.31; LM, 5.15; BIF, 2.67; BR, 5.39; BPB, 3.36; BM1 , 1.7 ; BN, 4.27; LIB, 5.2; ZB, 17.56; BB, 14.15; BZP, 2.73; DI, 1.7; HBC, 9.35; MFB, 2.45. Measurements of additional specimens are provided in table 3.

DISTRIBUTION: Thomasomys lojapiuranus is distributed in the montane forests of the western slope of the department of Piura, in northern Peru, and the province of Loja in southern Ecuador. All examined specimens are from north of the Huancabamba depression, most of them in the headwaters of the Río Huancabamba, a main tributary of the Río Chamaya (fig. 1). The altitudinal range is from 1198 m (but see Remarks) to 3481 m.

TAXONOMIC COMPARISONS: Thomasomys lojapiuranus differs from T. cinereus by its brownish dorsal pelage (vs. grizzled ashy gray to dark gray in T. cinereus ); whitish gray or pale brown ventral pelage (vs. pale yellowish or pale gray); mystacial vibrissae long, extending behind the posterior margin of pinnae by about half the pinnae length when laid back alongside the head (vs. shorter in T. cinereus , table 4); tail longer than head-and-body length (Tail% = 117±11% vs. 103±8%) and mostly unicolored (vs. moderately bicolored); thenar and hypothenar pads separated by a distinct gap (vs. thenar and hypothenar pads closely approximated); zygomatic notches shallow (vs. deep [55%] or shallow in T. cinereus ); incisive foramina long, but never extending posteriorly between the first upper molars (vs. usually extending between the first upper molars in T. cinereus ); stapedial process of bulla reduced (vs. conspicuous); orbicular apophysis elongated without basal constriction (vs. knob shaped in T. cinereus ); M1 anteromedian flexus, M3 hypoflexus, and m1 anteromedian flexid weak (vs. all these traits distinct; table 4). T. lojapiuranus also differs from T. cinereus in the morphology of glans penis by exhibiting a lateral notch, lack of dorsal groove, and spineless urethral flaps and dorsal papilla. Additionally, interdental ruga i4 extends to the palatal midline (vs. interdental ruga i4 shorter in T. cinereus ).

Thomasomys lojapiuranus differs from T. shallqukucha by its long mystacial vibrissae that extend conspicuously behind the posterior margin of pinnae when laid back alongside the head (vs. mystacial vibrissae shorter, barely extending behind the posterior margin of the pinnae in T. shallqukucha ); plantar surface of hind foot pale (vs. dark); zygomatic notch shallow (vs. very shallow); interparietal bone moderately long anteroposteriorly (vs. conspicuously long anteroposteriorly); incisive foramina long, extending posteriorly to the anterior margins of the first molars (vs. short, not approaching the anterior margins of the first molars); palatal median process usually present (vs. absent); Eustachian tube short and broad (vs. short and narrow); orbicular apophysis elongated without basal constriction (vs. elongated with basal constriction on anterior margin); M1 anteromedian flexus, M3 hypoflexus, and m1 anteromedian flexid weak (vs. all flexi distinct; table 4). Thomasomys lojapiuranus also differs from T. shallqukucha in the morphology of glans penis by presenting a lateral notch.

Thomasomys lojapiuranus differs from T. pagaibambensis by having a tail without a white tip (vs. tip usually white in T. pagaibambensis ); plantar surface of hind foot pale (vs. slightly darker); zygomatic plates moderately sloped backward (vs. vertically oriented); zygomatic process of maxilla and zygomatic process of squamosal closely approximated (vs. processes distinctly separated by a narrow jugal); incisive foramina long, extending posteriorly to the anterior margins of the first molars (vs. short, not approaching the anterior margins of the first molars); palatal median process usually present (vs. usually absent); Eustachian tube short and broad (vs. short and narrow); orbicular apophysis elongated without basal constriction (vs. elongated with basal constriction and recurved); capsular process of lower incisor alveolus absent (vs. distinctly swollen; table 4). Thomasomys lojapiuranus also differs from T. pagaibambensis in penis morphology by exhibiting a lateral notch and lack of dorsal groove, and in stomach morphology by exhibiting a shallower incisura angularis and a bordering fold little recurved to the left.

Thomasomys lojapiuranus could also be confused with some species of similar size of the Cinereus Group from Ecuador, such as T. silvestris , T. caudivarius , and the recently described T. salazari . However, T. lojapiuranus has the tail proportionally shorter (Tail% = 117%), whereas T. silvestris , T. caudivarius , and T. salazari have the tail longer (Tail%>130%; Brito et al., 2019: table 2). Thomasomys lojapiuranus has a broad rostrum with anterior half of nasals expanded that clearly differs from the narrower rostrum and nasals of T. caudivarius , T. salazari , and T. silvestris (fig. 24; Brito et al., 2019: fig. 6, S2). Also, the cranium of T. lojapiuranus has a more rectangular dorsal profile versus a more triangular profile in T. caudivarius , T. salazari , and T. silvestris (fig. 12B; Brito et al., 2019: fig. 6, S2). Additional comparisons are presented in table 4 (this work) and Brito et al. (2019: table 2).

NATURAL HISTORY: This species inhabits the humid montane forests of northern Peru and southern Ecuador, which has also been called the Peruvian Yungas ecoregion of the Tropical and Subtropical Moist Broadleaf Forest biome ( Dinerstein et al., 2017). At several collecting localities, the vegetation consisted of high shrubs and small trees, 10 to 15 m high.

Among specimens with reproductive data, 13 males were collected from July to August (usually considered the dry season); eight of them had scrotal testes (length> 10 mm) and five had abdominal testes (length ≤ 9 mm). No data is available for the wet season. Among 24 female specimens collected in July and August, 18 specimens had closed vagina (75%); three females had embryos (one with a fetus on the left ovary; the second with two embryos, one on each side; and the third with three embryos, two on the left, one on the right side); and three females were lactating; suggesting that during the dry season most specimens of T. lojapiuranus are in nonreproductive condition. Six specimens collected in November and December had no embryos.

Stomach contents of four specimens contained insect remains and seeds. Some nematodes were also found in the antrum.

In Yacurí National Park, Ecuador, Thomasomys lojapiuranus is sympatric with T. taczanowskii and T. caudivarius ( Lee et al., 2018) .

ETYMOLOGY: It is a pleasure to dedicate this species to the people of Loja and Piura departments, from Ecuador and Peru, respectively, who share similar costumes and traditions. We recognize in the distributional range of this mouse the fact that nature does not observe political boundaries.

REMARKS: Brito et al.’s (2019: fig. 3) phylogenetic analysis of the Cinereus Group contains several problematic identifications. Among others, they identified several specimens that appear as terminals in a phylogenetic tree (QCAZ 15612–15630) as Thomasomys cinereus . The authors did not report the collection localities of those specimens, but according to Lee et al. (2015: fig. 1), these were collected in 2015 near Laguna Negra (4.71308°S, 79.43025°W; 3407 m) in Loja province, Ecuador. We found that the sequences of four of these specimens are not T. cinereus sensu stricto nor any of the new species reported here (table 1, fig. 4). Additionally, Brito et al. (2019: apéndice 1) identified several specimens (QCAZ 16230, 16231, 16328–16330) from Jimbura (4.71167°S, 79.4403°W; 3226 m) as T. cinereus or “ Thomasomys sp. 2 ” ( Brito et al., 2019: fig 3); based on our sequence analyses (fig. 4), we would identify these specimens as T. lojapiuranus . Lastly, we sequenced one specimen (MEPN 12549) from Espínola, Parque Nacional Yacuri, Loja (4.719803°S, 79.439031°W; 3274 m) that Brito et al. (2019) identified morphologically as T. cinereus and determined that it too is T. lojapiuranus (fig. 4).

Several specimens from Piura, Huancabamba, Canchaque, Tambo, at 1198 m (FMNH 83444– 83454) were collected at an unusually low elevation for Thomasomys (Pacheco 2015) . Unusually too, most of the habitat around Canchaque corresponds to dry forest (VP, personal obs.), which suggests that the elevation provided for those specimens is inaccurate. On the other hand, two specimens were collected nearby (15 road km E Canchaque; LSUMZ 19315, 19316) but at 1737 m, which suggests that the locality of the FMNH specimens is likely correct, but perhaps not the elevation. The latter locality (at 1737 m) would be the lowest elevation record for T. lojapiuranus if the elevation data of the FMNH specimens were not considered.