Neacomys spinosus ( Thomas, 1882 )

Hurtado, Natali & Pacheco, Víctor, 2017, Revision of Neacomys spinosus (Thomas, 1882) (Rodentia: Cricetidae) with emphasis on Peruvian populations and the description of a new species, Zootaxa 4242 (3), pp. 401-440 : 413-414

Neacomys spinosus ( Thomas, 1882)

Large Spiny Mouse

Neacomys spinosus spinosus: Gyldenstolpe, 1932:34 N [eacomys]. s [pinosus]. typicus Thomas, 1900:153 Oryzomys spinosus : E.- L. Trouessart, 1897:528

Hesperomys (Oryzomys) spinosus: Thomas, 1884:448 Hesperomys (Calomys) spinosus Thomas, 1882:105

Lectotype. BMNH 81.9.7.25, adult male, skin, and skull, collected in 1801 by M. Stolzmann without collector number.

Type locality. “…Huambo.- a plantation in the forest of the same name, to the east of Chachapoyas and Chirimoto, 3700 feet in altitude, on the banks of the river Huambo, a tributary of the Huallaga…”, Thomas, 1882:99, approximately 1127 m, 6°34’S, 77°22.5’W, Huambo, Chachapoyas, Amazonas, Peru ( Fig. 6 )

Emended diagnosis. Neacomys spinosus is distinguished from other congeners by the combination of the following characters: reddish dorsal fur, long genal vibrissae, pale white ventral fur with gray bases, short carpal vibrissae, carpal and metatarsal patches always present, large forefeet, long tail, tapering rostrum, supraorbital beads moderately developed, inner border of the incisive foramina is posteriorly parallel, alisphenoid strut always present, large and slim condylar process, procingulum of M1 anteriorly flattened, short posteroloph, and deep protoflexus in M1.

Distribution. Neacomys spinosus is distributed in the Peruvian mountain cloud forests of Amazonas, San Martín, and Huánuco, from Southern Rio Marañon to Northern Rio Huallaga; elevation range is from 1127 to 2100 m.

Morphological description. Medium size. Dorsal fur is reddish brown; soft hairs are dark brown with reddish-orange tips and spines are white with black tips; dorsal hair length is 9 mm in average at the rump level; flanks are reddish. Ventral fur is white with gray on the basal half; ventral fur length is 4 mm in average at belly level. Hairs of ungual manus tufts pass claws slightly. Fifth forefeet digit passes the second interphalangeal joint of the fourth digit. Metacarpal patch is large, between second and fourth digit, with dark scales and hairs. Carpal vibrissae are short reaching the base of the fifth digit. Genal vibrissae pass the posterior border of the pinna. Superciliary vibrissae do not pass the posterior border of the pinna. Interramal vibrissae are inserted in a basal protuberance. Hind feet are thick and large, almost twice forefeet length. Ungual pedal tufts do not pass claws. First pedal digit reaches second digit base; the fifth digit reaches the second interphalangeal joint of the fourth digit. Metatarsal patch is present. Plantar squamation is restricted to pad region. Tail is approximately 20 % longer than head-body length. Upper hairs of the tail are black, covering 1.5–2 scales; lower hairs are whitish, covering 2 scales. Terminal pencil presents scarce long hairs.

Skull. ( Fig. 7 ) Dorsal view. Rostrum is broad and tapering. Anterior borders of the nasals are rounded. Posterior borders of the nasals are irregularly rounded, behind premaxillary-maxillary-frontal joint and maxillaryfrontal-lacrimal joints. Sutures between premaxillary and frontal bones are short and separate. Zygomatic notch is shallow; not enclosing the lacrimal foramen. Lacrimals are rounded; two-third dips in frontal bone, one-third dips in zygomatic bone. Interorbital beads are moderately developed.

Lateral view. Skull profile is flattened. Rostrum is anteriorly flat. Gnathic process is small. The most anterior part of the suture between nasal and premaxillary bones does not reach the squamosal zygomatic root. Breadth of the maxillary root of zygomatic is one-third upper row molar length. Breadth of the zygomatic plate and the squamosal root of zygomatic are subequal. Ethmoid and sphenopalatine foramina are placed at the anterior border of the M2. Ethmoturbinals are square shaped and its diameter is about one-half of M3. Alisphenoid strut is always present. Tegmen tympani do not overlap the posterior process of the squamosal. Orbicular apophysis of the malleus bone is large and globose; manubrium is large, and the lamina is rectangle and deep. Processus brevis of the incus is smaller than the incus breadth. Postglenoid foramina are continuous with the middle lacerate foramina. Mastoid tubercle is interiorly concave. Dorsal margins of postglenoid foramina and subsquamosal fenestra are rounded and reach the upper border of the mastoid. Hamular process is thick. Mastoid perforation is always present, with variable position, size, and shape.

Ventral view. Inner borders of the incisive foramina are posteriorly parallel. Incisive foramina breadth is about the length of M2-M3. Septum is narrow. Diastema is flat. Origin of the superficial masseter is circular and flat, placed at the anterior border of the zygomatic plate. Maxillary-palatine suture is placed among hypocone and hypoflexus of M1. Posterior palatine foramina are at the protoflexus level of M2. Posterolateral palatal pits are large and ovoid shaped, ranging from hypocone of M3 to the anterior mesopterygoid border. Sphenopalatine vacuities are large, occupying the basisphenoid and presphenoid area, with irregular borders. Presphenoid is triangle shaped, and broad with straight borders. Mesopterygoid fossa breadth is subequal to incisive foramina breadth. Parapterygoid processes are parallel; laterally, they reach to molar surface level. External borders of the pterygoid plate are straight. Fontanellae breadth is as M3 length. Posterior opening of the alisphenoid canal is broad, as M2 breadth. Groove of the infraorbital branch of the stapedial artery is deep. Middle lacerate foramina breadth is half of M2 length. Eustachian tube is short and wide. Bullas are globular. Anterior process of bullae is in contact with the pterygoid plate. Basioccipital breadth is subequal to breadth between second upper molars, at petrosal level. Basioccipital pits are shallow. Anterior border of the foramen magnum is obtuse V-shaped.

Jaw. Masseteric crest is below the procingulum the m1. Mental foramen is at the labial border of the diastema. Capsular process is moderately developed, but does not pass the condylar process. Coronoid process is short and thick. Condylar process is large and thin. Angular process is short. Crest between the condylar and angular process is shallow. Ventral border of the jaw is slightly concave.

Teeth. Upper. Incisors are opisthodont, with rounded tips and yellow-orange enamel bands. Molar rows are parallel. Procingulum of M1 is anteriorly rounded, narrow and symmetrically divided. Anteroflexus of M1 reaches labial surface. Mesoloph of M1 is perpendicular to the labial surface. Posteroloph of M1 reaches the labial surface. Anteroloph of M2 is thin and reaches the labial surface. Protoflexus of M2 is shallow. Mesoloph of M2 is perpendicular to the labial surface. Posteroloph of M2 reaches the molar surface. Posterior border posteroloph of M2 is rounded. Anteroloph of M3 reaches the paracone surface. Lower. Procingulum of m1 is symmetrically divided. Mesolophid of m1 is narrow. Hypoflexid of m1 is perpendicular to the labial surface. Posterior border of posterolophid of m1 is convex, does not reach the lingual surface. Anterolabial cingulum of m2 is broad. Posterior border of posterolophid of m2 is convex and reaches the lingual surface.

Natural history. Neacomys spinosus is an endemic species from Peru, with restricted distribution to Mountain cloud forests between Marañón and Huallaga Rivers. Not much is known about this species. Leo & Romo (1992) recorded some individuals in the headwaters of the Río Abiseo , within the Parque Nacional Río Abiseo , and reported the highest altitudinal range of this species (2375 m). They also mentioned that specimens were collected on the ground, in riverine vegetation in a sandy beach, with traps placed above cane and shrubs a few centimeters above the ground.

Remarks. Thomas (1900) used N. s. typicus to name individuals from the type series of N. spinosus , which were compared with N. s. tenuipes . For this reason, typicus is still considered a junior synonym of N. spinosus .

Figures

FIGURE 6. Illustration map showing the distribution of N. spinosus (light blue), N. a. amoenus (blue), N. a. carceleni (dark purple), N. amoenus “ CAA ” (white) and Neacomys vargasllosai sp. nov. (yellow). Diamonds indicate Type Localities, triangles indicate samples of DNA sequences; squares indicate morphologically revised specimens (qualitative and / or quantitatively); and circles indicate both molecular and morphological evidence. See Appendix I for locality numbers.

FIGURE 7. Dorsal, ventral, and lateral views of the cranium and the mandible of Neacomys spinosus (BMNH 81.9. 7.25, lectotype).