Neacomys amoenus amoenus Thomas, 1903

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: 414-416

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Neacomys amoenus amoenus Thomas, 1903


Neacomys amoenus amoenus Thomas, 1903 

Pleasant Spiny Mouse

Neacomys spinosus amoenus Thomas, 1903:239 

Holotype. Adult male, skin, and skull BMNH, collected 11th August 1902 by A. Robert, original number 1077.

Type locality. “…village situated at an altitude of about 800 m., on the Serra do Chapada , some thirty miles N.E. of Cubayá …”, Thomas , 1903:233, between 700 to 900 meters, approximately 15°30’S, 55°31’W, Serra do Chapada , Chapada do Guimarães, Cuiabá, Mato Grosso, Brazil ( Fig. 6View FIGURE 6).GoogleMaps 

Emended diagnosis. Neacomys amoenus amoenus  is distinguishable from other species for the combination of following characters: pale orange dorsal fur, pale yellowish flanks, ungual manus tufts do not pass the claws, metacarpal and metatarsal patches always absent, short carpal and genal vibrissae, slim and long forefeet, deep zygomatic notch, interorbital beads are moderately developed, inner border of the incisive foramina are posteriorly convergent, the origin of the superficial masseter ovoid and flat, medium size sphenopalatine vacuities, narrow basioccipital, short and broad condylar process, large posteroloph of M1, and shallow protoflexus of M2.

Distribution. Neacomys amoenus amoenus  inhabit in the Cerrado, in the Northern Mato Grosso in Brazil, and Northeastern Santa Cruz in Bolivia from 200 to 900 m.

Morphological description. Large size. Dorsal fur is pale Orange Brown; soft hairs are light brown with pale orange tips; spines are white with gray tips; fur length is 9 mm in average at the rump level; flanks are pale yellowish orange. Ventral fur is smoky white with the short gray base; its length is 4 mm in average at belly level. Ungual manus tufts do not pass the claws. Fifth digit of forefeet passes the first interphalangeal joint of the fourth digit. Metacarpal patch is absent. Carpal vibrissae reach the base of the fifth digit. Genal and superciliary vibrissae do not pass the posterior border of the pinna. Interramal vibrissae are inserted in a basal protuberance. Hind feet are slim and large, almost twice forefeet length. Ungual pedal tufts do not pass claws. First pedal digit reaches the first interphalangeal joint of second digit; fifth digit reaches the second interphalangeal joint of the fourth. Metatarsal patch is absent. Plantar squamation is on the pad and hypothenar region. Tail is around 5% longer than head-body length. Upper hairs of the tail are black, covering 1–2 scale; lower hairs are white and cover 1–2.5 scales. Tail scale length average is 1.1 mm. Terminal pencil of hairs presents scarce long hairs.

Skull. ( Fig. 8View FIGURE 8) Dorsal view. Rostrum is broad and truncated. Anterior borders of nasals are rounded. Posterior borders of nasals are irregular, is behind premaxillary-maxillary-frontal joint and maxillary-frontal-lacrimal joints. Dorsal sutures between maxillary-frontal are short. Zygomatic notch is deep, not enclosing lacrimal foramen. Lacrimals are rounded; one-half is inserted on the squamosal root of zygomatic. Lateral process of frontals is slightly developed. Interorbital beads are moderately developed.

Lateral view. Skull profile is flattened. Rostrum is anteriorly flat. Gnathic process protrudes slightly over incisor surface. The most anterior part of the suture between nasal and premaxillary bones reaches squamosal zygomatic root. Breadth of the maxillary root of zygomatic is as the M3 length. Breadth of the zygomatic plate is as M1 and one-half M2 length. Breadth of the squamosal root of zygomatic is smaller than the breadth of the zygomatic plate. Ethmoid foramen is at the middle point of M2 level. Sphenopalatine foramen is placed at the anterior border of M2. Ethmoturbinals diameter is as one-half of M3 length. Alisphenoid strut is always absent. Tegmen tympani do not overlap the posterior process of the squamosal. Mastoid tubercle is anteriorly concave. Apophysis orbicular of malleus bone is globose and short; the lamina is shallow. Processus brevis of the incus is large, subequal to the incus breadth. Dorsal margin of postglenoid foramina and subsquamosal fenestra are rounded. Hamular process is thick. Mastoid perforation is as M2 length and placed posteriorly.

Ventral view. Inner borders of the incisive foramina are posteriorly convergent. Incisive foramina breadth is about M2-M3 length. Septum is narrow. Diastema is flat. Origin of the superficial masseter is ovoid and flat, placed behind of the anterior zygomatic-plate border. Maxillary-palatine suture is at hypocone of M1 level. Posterior palatine foramina are at the protoflexus level of M2. Posterolateral palatal pits are small, placed at the anterior mesopterygoid border. Sphenopalatine vacuities are medium size, occupying the basisphenoid and presphenoid. Presphenoid is broad and triangular with straight lateral 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 one-half of M3 length. Posterior opening of the alisphenoid canal is broad, as M2 length. Groove of the infraorbital branch of stapedial artery is wide and deep. Middle lacerate foramina breadth is as M2 length. Eustachian tube is large and wide. Bullas are globular shaped. Anterior process of bullae is not in contact with the pterygoid plate. Basioccipital breadth at petrosal level is lesser than breadth between second upper molars. Basioccipital pits are shallow. Anterior border of the foramen magnum is obtuse V-shaped.

Jaw. Masseteric crest is below the procingulum of 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 thick. Condylar process is short and broad. Angular process is short. Crest between condylar and angular process is shallow and rounded. 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. Procingulum of M1 is broad and symmetrically divided. Anteroflexus of M1 reaches the labial surface. Mesoloph of M1 is perpendicular to the labial surface. Posteroloph of M1 reaches the labial surface; its posterior border is convex. Anteroloph of M2 is broad and reaches the labial surface. Protoflexus of M2 is shallow. Mesoloph of M2 is antero-posteriorly convex. Posteroloph of M2 reaches the molar surface. Posterior border of posteroloph of M2 is rounded. Anteroloph of M3 reaches the paracone surface. Lower. Procingulum of m1 is symmetrically divided. Mesolophid of m1 is broad. Hypoflexid of m1 is perpendicular to the labial surface. Posterior border of posterolophid of m1 is straight and reaches the lingual surface. Anterolabial cingulum of m2 is narrow. Posterior border of posterolophid of m2 is convex and reaches the lingual surface.

Natural history. Not much of Neacomys amoenus amoenus  is known, it inhabits in the Cerrado ecosystems within Brazil and Bolivia; which unfortunately are being deforested by anthropic activities. Nevertheless, given the distribution of N. a. amoenus  , two areas of preservation could keep this species: Parque Nacional da Chapada dos Guimarães in Brazil ( and Parque Nacional Noel Kempff Mercado in Bolivia ( 

Remarks. Patton et al. (2000) suggested keeping “ amoenus  ” as a junior synonym of N. spinosus  , based on comparisons between the type series of “ amoenus  ” with individuals of N. spinosus  from Juruá River. However, those specimens named spinosus  are here referred as clade N. amoenus  “Central Andes-Amazonia” (see below, also Appendix II).














Neacomys amoenus amoenus Thomas, 1903

Hurtado, Natali & Pacheco, Víctor 2017


Neacomys spinosus amoenus

Thomas 1903: 239