Neacomys marci Brito & Tinoco, 2023

Tinoco, Nicolas, Koch, Claudia, Colmenares-Pinzon, Javier E., Castellanos, Francisco X. & Brito, Jorge, 2023, New species of the Spiny Mouse genus Neacomys (Cricetidae, Sigmodontinae) from northwestern Ecuador, ZooKeys 1175, pp. 187-221 : 187

Neacomys marci Brito & Tinoco sp. nov.

Neacomys tenuipes : Brito et al. 2021a; Curay et al. 2022 (non Neacomys tenuipes Thomas, 1900).

Holotype.

MECN 6232 (field number JBM 2307), an adult female captured on 18 November 2020, by J. Brito, J. Curay and K. Cuji, preserved as dry skin, skull, and skeleton, with muscle and liver sample preserved in 95% ethanol.

Measurements of holotype (in mm).

HBL 70; TL 84; HF 20; E 13; w 14.5; CIL 18.5; LIF 2.9; BIF 1.4; LD 5.3; LM 2.5; AW 4; BPB 2.1; LR 6.4; LN 8.2; RW-2 4; LIB 4.2; OL 6.6; BZP 1.7; ZB 11; BB 10.4; OCB 5; BOL 3.1; CD 8.1; BM1 0.8. All measurements of the type series are listed in Table 4 .

Type locality.

Reserva Dracula, Estación Fisher, Parroquia Chical, Cantón Tulcán, Provincia Carchi, Ecuador, Coordinates: 1.006667, -78.2247; WGS84 taken by GPS at the site of collection; elevation 1,067 m.

Paratypes

(n = 38). MECN 6230, adult male, and MECN 6233, adult female, preserved as dry skin and cleaned skull, collected in Provincia de Carchi, Reserva Dracula, Estación Fisher (1.006667, -78.2247, 1,067 m.) on 18 November 2020, by J. Brito, J. Curay and K. Cuji. MECN 6231, adult male, preserved as dry skin and cleaned skull, collected in Provincia de Carchi, Reserva Dracula, Estación Fisher (1.006667, -78.2247, 1,067 m.) on 20 November 2020, by J. Brito, J. Curay and K. Cuji. MECN 6238, MECN 6239, MECN 6240, MECN 6241, adult males, and MECN 6237, MECN 6242, adult females, preserved in 75% ethanol, collected in Provincia de Carchi, Reserva Dracula, Estación Fisher (1.006667, -78.2247, 1,067 m.) on 21 November 2020, by J. Brito, J. Curay and K. Cuji. MECN 6479, adult male, preserved in 75% ethanol, collected in Provincia de Carchi, Reserva Dracula, Estación Fisher (1.006667, -78.2247, 1,067 m.) on 30 March 2021, by J. Brito. J. Castro, Z. Villacís and J. Guaya. MECN 5339, MECN 5340, MECN 5374, MECN 5375, adult males, preserved as cleaned skulls and carcasses in ethanol, MECN 5370, MECN 5373, adult males, preserved in ethanol, MECN 5372, adult female, preserved as cleaned skull and carcass in ethanol, collected in Provincia de Carchi, Reserva Drácula, Peñas Blancas (0. 973758, -78.210173, 1,290 m) on 27 November 2016, by J. Brito, J. Robayo and H. Yela. MECN 5357, adult male, preserved as cleaned skull and carcass in ethanol, collected in Provincia de Carchi, Reserva Dracula, Pailón (0.992406, -78.237714, 1,270 m) on 29 November 2016, by J. Brito, J. Robayo and H. Yela. MECN 6013, juvenile male, preserved as cleaned skull and carcass in ethanol, collected in Provincia de Carchi, Reserva Dracula, Pailón (0.992406, -78.237714, 1,270 m) on 7 November 2017, by J. Brito, J. Curay and R. Vargas. MECN 5919, adult male, preserved as cleaned skull and carcass in ethanol, collected in Provincia de Carchi, Reserva Dracula, Pailón Alto (0.97415, -78.2176, 1,630 m) on 28 March 2018, by J. R. Vargas and M. Esparza. MECN 5904, adult male, preserved as dry skin and cleaned skull, MECN 6014, adult male, MECN 6015, juvenile male, MECN 6016, adult female, preserved in ethanol, collected in Peñas Blancas on 7 November 2017, by J. Brito, J. Curay and R. Vargas. MECN 6570, adult male, preserved as cleaned skull and carcass in ethanol, collected in Provincia de Imbabura, Parroquia Lita, Aguinaga (0.78125, -78.318113, 1,400 m) on 1 March 2020, by S. Erazo and D. Mantilla. MECN 6271, adult male, preserved in ethanol, collected in Provincia de Imbabura, Reserva Río Manduriacu (0.309547, -78.856631, 1,200 m) on 12 September 2019, by R. Peña. MECN 6766, adult female, preserved as skin dry, skull and skeleton, collected in Pichincha, Reserva Chontaloma (0.18138, -78.90516, 630 m) on 15 March 2021, by S. Pozo and C. López. MECN 7125, juvenile female, preserved as cleaned skull and carcass in ethanol, collected in Pichincha, El Progreso (0.164608, -78.767156, 1,140 m) on 21 September 2021, by R. Garcia. QCAZ 18677, adult male, preserved as dry skin and clean skull / jaw, collected in Pichincha, Reserva Mashpi (0.166600, -78.880000, 900 m) on 26 September 2019, by J. Cook and J. Dunnum. MECN 7563, MECN 7568, adult females, and MECN 7569 adult male, preserved as dry skins and cleaned skulls, MECN 7572, adult female, and MECN 7560, 7561, 7565, 7570, 7573 adult males, preserved as cleaned skull and carcass in ethanol, collected in Provincia de Esmeraldas, Reserva Canandé, Gualpí de los Cayapas (0.56479, -79.06104, 450 m) on 14-16 October 2022, by J. Brito, J. Guaya, and A. Aguilar.

Etymology.

Named in honor of Marc Hoogeslag of Amsterdam, the Netherlands. He was co-founder and leader of the innovative Land Acquisition Fund of the International Union for the Conservation of Nature - Netherlands, which helps local groups throughout the world to establish new ecological reserves and conserve endangered species. Fundacion EcoMinga’s Reserva Manduriacu, the habitat of this new species, is one of the many reserves which have benefited from Marc’s program. The species epithet is formed from the surname “Marc” taken as a noun in the genitive case, adding the Latin suffix “i” (ICZN 31.1.2).

Diagnosis.

A species of Neacomys with the following combination of characters: small size (head-body length 65-85 mm), long tail (69-126% longer than head and body length), belly fur pale buff but with gray based hairs, white throat, long nasals (which extend well beyond the plane of the lacrimal), condylar process higher than coronoid process, M1 anterocone divided, M1 with broad protoflexus; m1-m3 with wide hypoflexids.

Morphological description.

The following description was based on all specimens available. Neacomys marci sp. nov. is a spiny mouse of small size (head and body length 65-85 mm). The dorsal pelage is dark brown (Fig. 3 ); soft hairs are mixed with spines; on average dorsal hairs are 9-10 mm in length. The soft hair is tricolor, with a light brown band at the base, an orange band in the middle and a black apical band. The posterior mystacial vibrissae are thick and long (34 mm), surpassing the auricular pinnae when ad pressed back; two superciliary vibrissae, the longest measuring 39 mm, extending to the middle of the dorsum. One medium-sized genal vibrissae (32 mm) are also present, which are more slender than the mystacial vibrissae. The ears are large (12-16 mm) and oval in outline. Although the ears seem to be naked, they are covered with short black fringe of hair. The base of the internal ears is yellowish cream and the edges are dark, the hairs are yellowish and medium in size. A small pale orange postauricular patch is present.

The pelage on the throat is white (Fig. 4A ) and extends up to the corners of the mouth. The ventral pelage is pale buff but with gray base, and the hairs are on average 3.0-3.5 mm in length at the middle of the belly. The tail is uniformly dark, slender, and long (69-126% longer than head and body length). It is covered with rectangular scales (13 or 14 rows/cm near the base), with three dark brown hispid hairs emerging from the base of each scale, not longer than 1.5-2 scale rows. The hairs of the terminal portion of the tail form a small tuft (<3 mm). Females have eight mammae arranged in pectoral, thoracic, abdominal, and inguinal pairs.

The manus is slender and short. The first digit is reduced with a long and wide claw. The other claws are short and curved. Ungual tufts are white and extend beyond the claw ends. The dorsal surface with evident brown scales; each scale has three dark brown hairs and sometimes the central hair is the longest. Long carpal vibrissae can reach the claw of digit V. The digits are relatively large; digit I is substantially shorter than digit II; digit II is shorter than digit III; digit III is slightly larger than digit IV; digit IV is larger than digit V.

Hind feet are long and slender (18-22 mm); the ungual tufts are white, abundant and extend well beyond the edge of the claws (Fig. 5A, D ). Their dorsal surface has a small metatarsal patch, with brown scales (Fig. 5D ); each scale has three dark brown hairs. Large number of granules covers most of the plantar surface, including the spaces between the pads and reaching the anterior border of the thenar pad. The four interdigital pads are elevated and similar in size; pads II and III are separated by a small interspace, while pads II and IV are separated by an interspace of similar size than pad I (Fig. 5A ). The hypothenar pad is very small or absent, while the thenar pad is well developed, large and elevated anteriorly. Digits are relatively short; digit I reaches the base of digit II; digit II is slightly shorter than digit III; digit III is slightly larger than digit IV; digit IV is larger than digit V; digit V reaches halfway of the first phalanx of digit IV (Fig. 5A, D ); claws are short, recurved and basally opened.

The cranium is moderately large for the genus (average CIL = 18.2 mm) with the braincase showing a convex profile (Fig. 6 ). The dorsal profile of the cranial roof is flat from the nasals to the middle of the frontals, then rises at the back of the frontals and slopes gently down the parietals toward the occiput; the rostrum is long and slender; premaxillae are slightly shorter than nasals, not extending anteriorly beyond incisors, without forming a rostral tube; gnathic process is very small; the suture between the nasal bones and the premaxillary reaches the root of the zygomatic bone; the nasal bone is wide at the base and gradually widens forward (Fig. 7 ); the interorbital region is narrow; the supraorbital edges are small and sharp; the zygomatic notches are shallow and wide while seen from above; in the olfactory sagittal plane are two frontoturbinals, one interturbinal and three ethmoturbinals present (Fig. 8F ); the lachrymal is small, with contact in equal proportions with the frontal and maxillary; the post-nasal depression is shallow; the fronto-parietal suture is V-shaped; the parietal is restricted to the dorsal portion of the skull; the braincase is rounded and inflated. A gnatic process is not developed; the zygomatic plate is wide and excavated (> M1 length) and slightly inclined backward; the zygomatic arch slender and without a jugal; a squamosal-alisphenoid groove is visible through the translucent braincase (Fig. 8B, E ), with a perforation where it crosses the depression for the masticatory nerve; the stapedial foramen is present and small, the carotid canal is small, and the petrotympanic fissure is expressed (Figs 8C ); the cephalic arterial supply is primitive (pattern 1 of Voss 1988); the alisphenoid strut is absent; an anterior opening of the alisphenoid canal is absent; the postglenoid foramen is large; the subsquamosal fenestra is small and the hamular process of the squamosal is long; a small tegmen tympani is present (Fig. 8A ); there is no contact between the anterodorsal edge of the ectotympanic and the mastoid tubercle, which leads to an opened ectotympanic ring (Fig. 8A ); the orbicular apophysis of the malleus is wide and elongate (oval in shape), with its longitudinal axis inclined towards the manubrium; mastoid bears no dorsolateral fenestra; the paraoccipital process is short.

The Hill foramen is tiny; the incisive foramina are short, ending well anterior to the M1s anterior faces; the capsular process of the premaxillary is well developed; the palate is wide and long with the anterior border of the mesopterygoid fossa not reaching M3s posterior faces; the palatal foramina are small; the posterolateral pits are long and paired, and located parallel to the anterior part of the mesopterygoid fossa; the mesopterygoid fossa is broad as the parapterygoid plates, with the anterior margin U-shaped (Fig. 8D ); the shape of the pterygoid plate is not expanded, and has straight margin; the sphenopalatine vacuities are elongated and narrow, occupying the posterior part of the presphenoid area; the presphenoid is wide (Fig. 8D ); the auditory bullae are small and flask-shaped; the Eustachian tube is short, wide and gradually constricted; the petrosals are well-exposed; the anterior bullae process is in contact with the posterior margin of the pterygoid plate (Fig. 8C ); the basioccipital depressions are deep, forming an recognizable crest; the anterior border of the foramen magnum is narrow, with a conspicuous notch.

The mandible with masseteric crest in line with procingulum of m1; the coronoid process is small, slender, and bended backwards; the sigmoid notch is oval; the condylar process is large and robust; the capsular process is forming a rounded elevation that lies below the coronoid process; the angular notch is shallow, and the angular process is blunt.

The incisors are opistodont, without grooves, and with yellowish enamel; the molars are brachydont and terraced (Fig. 9A ); the main cusps of the upper and lower molars are opposed. The M1 is rounded in outline; the procingulum is narrower than the rest of the molar, with a rounded anteromedian fossette present; anterocone divided; the protoflexus is broad; the mesoflexus is small; the metaflexus is large and wide; the posteroloph is small. The M2 with indistinct protoflexus; the anteroloph is small; the mesoflexus is short and wide; the mesoloph is short; the mesofosette is rounded (Fig. 9A ); the posteroloph is similar to M1. The M3 has a small paraflexus and indistinct hypoflexus. The upper molars have three roots each. The m1 is rectangular in outline; the procingulum is not divided into labial and lingual conulids; the protoflexid is short and wide; the hypoflexid is wide; the mesoflexid is large and wide; the mesolophid is large; the posteroflexid is short and broad; the mesofosette is large. The m2 is square in outline; the protoflexid is large and narrow; the hypoflexid is wide and inclined with direction towards the posteroflexid; the mesoflexid is short and wide; the mesolophid is short and wide; the mesofosette is very small. The m3 is anteriorly-posteriorly compressed, having a wide hypoflexid and a small anterolabial cingulum. The lower molars have two roots each.

The tuberculum of the first rib articulates with the transverse processes of the seventh cervical and the first thoracic vertebrae; the second thoracic vertebra has a differentially elongated neural spine; 19 thoracicolumbar vertebrae, the 16th with moderately developed anapophyses; four sacrals; 33 or 34 caudals, with complete hemal arches in the second, third and fourth; 12 ribs.

The gall bladder is absent. The stomach is unilocular and hemiglandular; the cornified epithelium lines the corpus, while the glandular epithelium occupies the antrum and is slightly extended to the left of the esophageal opening; the bordering fold is notorious for being thick and long, surpassing the left level of the incisura angularis; the incisura angularis is moderately deep and the plica angularis is well expressed with a well-developed pars pyloricus (Fig. 10 ).

Comparisons with similar species.

Neacomys marci sp. nov. differs from its sister species N. tenuipes mainly in ventral coloration, N. marci sp. nov. is pale buff with white throat, while N. tenuipes is completely white to pale orange (Fig. 4 ). Additionally, N. marci sp. nov. has a slight bicolor at the base tail, while N. tenuipes has a clear bicolor at the base. The condylar process in N. marci sp. nov. is higher than the coronoid process, while in N. tenuipes most are lower than the coronoid process, some are equal to the coronoid process. At the molar level, N. marci sp. nov. has a narrow anterocone of M1, while in N. tenuipes it is wide (Fig. 4 ). In N. marci sp. nov. the hypoflexus of M3 is indistinct or absent, while in N. tenuipes it is present and well evident.

Another species from the Chocó Biogeographic region with which Neacomys marci sp. nov. could be confused is N. pictus . Both species have white throats, however N. marci sp. nov. has pale buff ventral color and N. pictus is faintly plumbeous basally on the belly. Neacomys marci sp. nov. has the interorbital region (in ventral view) with developed ridges, projecting like ledges; whereas N. tenuipes it is hidden under the maxilla. The mastoid is ossified in N. marci sp. nov. while in N. tenuipes it is most perforated. Other comparisons are summarized in Table 5 .

Distribution.

Neacomys marci sp. nov. is known from six localities in the provinces of Carchi, Pichincha, and Esmeraldas, in northwestern Ecuador (Fig. 11 ).

Natural history.

The distributional range of the species is thus far limited to the Chocó Biogeographical region ( Myers et al. 2000), where it occupies the lower subtropical and lower montane ecosystems (Ceron et al. 1999), in an altitudinal range from 450 to 1,630 m (Fig. 12 ). These forests are characterized by having a tree cover of approximately 30 m height. Most of the vegetation belongs to the families Araceae , Melastomataceae , Cyclanthaceae , Bromeliaceae , and to the ferns. Additionally, the following species of rodents and marsupials were recorded as living in sympatry: Melanomys caliginosus , Mindomys hammondi , Oecomys sp., Rhipidomys latimanus , Tanyuromys thomasleei , Pattonimus musseri , Sigmodontomys alfari , and Transandinomys bolivaris , the heteromyid Heteromys australis , the marsupials Chironectes minimus , Mamosops caucae , and Marmosa isthmica , and the squirrel Microsciurus mimulus .

Figures

Figure 3. Live specimen of Neacomys marci sp. nov. in its natural habitat (MECN 6230, Estacion Fisher, Ecuador). Please note the color of a living animal.

Figure 4. Ventral views of the skin of A Neacomys marci sp. nov. (MECN 6232, holotype; Estacion Fisher, Ecuador), and B Neacomys tenuipes (UIS-MHN-M 1723; Finca La Bufalera, Colombia). Note the white-furred throat in N. marci sp. nov. (arrowed).

Figure 5. Ventral (A-C) and dorsal (D-F) views of the hind foot of Neacomys marci sp. nov. (A, D MECN 6232, holotype; Estacion Fisher, Ecuador), N. tenuipes (B, E MHN-UCa-M 4019, Colombia), and N. rosalindae (C, F MECN 5824; Cordillera de Kutuku, Ecuador). Figures are not to scale to facilitate comparisons. Abbreviations: h = hypothenar, t = thenar, ut = ungual tufts.

Figure 6. Three-dimensional reconstruction of the skull of Neacomys marci sp. nov., based on micro-CT data of the holotype (MECN 6232; Estacion Fisher, Ecuador): cranium in dorsal, ventral, and lateral view, and left hemimandible in labial view. Scale bar: 5 mm.

Figure 7. Selected aspects of qualitative anatomy contrasted in the crania (dorsal view = A, ventral view = B) based on data of Neacomys marci sp. nov. (left; MECN 6232, holotype; Estacion Fisher, Ecuador) and Neacomys tenuipes (right; UIS-MHN-M 1723; Finca La Bufalera, Colombia). The figure portrays differences between the characteristics of these species as follows: N. marci sp. nov. has the longest nasal (n) extending well beyond the plane of the lacrimals (la), larger molars (m), and a low sagittal ridge (sr). Figures are not to scale to facilitate comparisons.

Figure 8. A selected anatomical features of the skull of Neacomys marci sp. nov. based on the holotype (MECN 6232; Estacion Fisher, Ecuador): posterior portion of the skull in lateral view B lateral view of alisphenoid bone region C right auditory region in ventral view D ventral view of basicranial region E dorsal view (roofing bones of braincase removed) of basicranial region F cross-section of the cranium. Abbreviations: ab, auditory bulla; bet, bony Eustachian tube; bmt, buccinators-masticatory trough; bo, basioccipital; bs, basisphenoid; cc, carotid canal; etI, ethmoturbinal I; etII, ethmoturbinal II; etIII, ethmoturbinal III; fo, foramen ovale; ft 1, frontoturbinal 1; ft 2, frontoturbinal 2; it, interturbinal; ls, lamina semicircularis; mas, mastoid capsule; mlf, middle lacerate foramen; palc, posterior opening of the alisphenoid canal; pet, petrosal; pgf, postglenoid foramen; ppp, posterior palatal pits; ps, presphenoid; sag, squamosal alisphenoid groove; sfr, sphenofrontal foramen; stf, stapedial foramen; ssf, subsquamosal fenestra; tt, tegmen tympani; Pictures are three-dimensional reconstructions based on micro-CT data.

Figure 9. A, B occlusal view of the right upper, and C, D right lower tooth row of: (A, C) Neacomys marci sp. nov. (MECN 6232, holotype; Estacion Fisher, Ecuador) and (B, D) N. tenuipes (B UIS-MHN-M 1723; Finca La Bufalera, Bolivar, Colombia, and D MHN-UCa-M 3647; Acevedo, Huila, Colombia). Abbreviations: alc, anterolabial conule; pf, paraflexus; f, mesofosette; pc, procingulum. The arrows indicate the direction of the mesoflexus with the hypoflexus.

Figure 10. Stomach of Neacomys marci sp. nov. (MECN 7568; Reserva Rio Canande, Ecuador) A dorsal view B ventral view. Abbreviations: b, bordering fold; d, duodenum; co, cornified epithelium; ge, glandular epithelium; i, incisura angularis; e, esophagus.

Figure 11. Topographic map of northern South America. Sampling localities of three Neacomys species are shown with color codes described in the legend. Neacomys marci sp. nov. localities correspond to the Choco biogeographic region in northwestern Ecuador (type locality is shown with black circle).

Figure 12. Habitat where specimens of Neacomys marci sp. nov. have been collected in this study A Piemontane forest, and B Choco rainforest.