Neacomys vossi, Semedo & Silva & Gutiérrez & Ferreira & Nunes & Mendes-Oliveira & Farias & Rossi, 2020

Semedo, Thiago Borges Fernandes, Silva, Maria Nazareth Ferreira Da, Gutiérrez, Eliécer E., Ferreira, Daniela Cristina, Nunes, Mario Da Silva, Mendes-Oliveira, Ana Cristina, Farias, Izeni Pires & Rossi, Rogério Vieira, 2020, Systematics of Neotropical Spiny Mice, Genus Neacomys Thomas, 1900 (Rodentia: Cricetidae), from Southeastern Amazonia, with Descriptions of Three New Species, American Museum Novitates 2020 (3958), pp. 1-43 : 26-30

Neacomys vossi , new species

Voss’s Spiny Mouse Figures 8 , 9

HOLOTYPE: The holotype ( UFPA 1583 ) is an adult female (age class 2) collected on 2 April 2013, by Ana Cristina Mendes Oliveira (original field number JB 031 ). The specimen consists of a stuffed skin, skull, and skeleton, all in good condition; additionally, a tissue sample is preserved in ethanol, and a partial cytochrome b sequence that we obtained from it has been deposited in Genbank with accession number MT 462028 .

TYPE LOCALITY: Boca do Rato , on the right bank of the Rio Tapajós , Itaituba municipality, state of Pará, Brazil (5°14′S, 56°56′W, fig. 5) .

DIAGNOSIS: Neacomys vossi is a small species (table 3) that differs from congeneric taxa by the following combination of craniodental traits: skull delicate; interorbital region narrow; nasal bones expanded anteriorly; supraorbital margins convergent anteriorly; subsquamosal fenestra usually small (about ¼ the size of the postglenoid foramen on each side of the skull); paroccipital processes close to the auditory bullae; sphenopalatine foramen large; carotid circulation pattern 1 (sensu Voss, 1988); maxillary part of incisive septum (between the incisive foramina) usually wide; M1 usually with slightly flat, narrow, and undivided anterocone; and M1 anteroloph usually distinct (not fused with the anterolabial conule).

MORPHOLOGICAL DESCRIPTION: Dorsal pelage brown sprinkled with orange and/or black (fig. 8); ventral pelage varying from pure white to buffy white; very thin orange lateral line. Superciliary, genal, and mystacial vibrissae blackish and long (extending behind ears when laid back alongside the head); submental vibrissae absent; interramal vibrissae short and white. Ears small and rounded; post-auricular hairs gray-based with orange tips, forming an orange tuft behind each pinna. Ungual tufts white, longer than claws; fore- and hind feet covered dorsally with buffycream hairs; hind feet narrow and elongate with small interdigital membranes. Tail about the same length as head and body, usually slightly bicolored (except in UFPA 1277, 1417, 1444, 1654, and 1736 which have unicolored tail) and covered by spiny and clearly visible hairs; tail tip of the tail with very short (approximately 1.4 mm long) terminal tuft; caudal scales small, arranged in annular series; each caudal scale with three subequal hairs inserted along its posterior margin.

Skull small and delicate in dorsal view (fig. 9); with expanded anterior nasal margins; notably broad rostrum and shallow zygomatic notches; posterior nasal terminus usually flat, extending beyond the maxillary-frontal suture; premaxillaries terminating slightly anterior to nasals; lacrimal bone small and visible in dorsal view, equally contacting maxillary and frontal bones; supraorbital margins convergent anteriorly; interorbital region narrow; supraorbital beads developed as projecting shelves; lateral expansion of the parietal restricted to the dorsal surface (except in UFPA 1227 and UFPA 1577, in which the parietal is slightly expanded ventrally near the squamosal root of the zygomatic arch). Incisive foramina small with subparallel lateral margins, not extending posteriorly to the level of M1s; maxillary portion of incisive septum (dividing the left and right foramina) usually wide. Zygomatic plate narrow. Palate with two posterolateral pits on each side of the palate. Auditory bullae small and globular, with short and narrow eustachian tubes; periotic bone extending anteriorly to internal carotid canal, but usually not entering into it (except in UFPA 1227, 1417, 1530, 1654, 1417, and 1736, in which the periotic does enter the internal carotid canal). Subsquamosal fenestra usually small (about ¼ the size of the postglenoid foramen); hamular process of the squamosal long. Paraoccipital process narrow, small, and close to the auditory bullae ( Sánchez-Vendizú et al., 2018: fig. 3C). Sphenopalatine foramen large; alisphenoid strut absent; carotid circulation primitive (pattern 1, as identified by retaining a well-developed squamosal-alisphenoid groove and sphenofrontal foramen, both indicative of the presence of the supraorbital branch of the stapedial artery; Voss et al., 1988).

First upper molar (M1) usually with slightly flat and undivided anterocone; anteroloph usually distinct (not fused with the anterolabial conule); M3 small; labial cusps (paracone, metacone) usually taller than lingual cusps (protocone, hypocone); m1 anteroconid undivided.

Mandible with mental foramen opening laterally; capsular process of lower incisor alveolus present, but indistinct (reduced as a slight, rounded elevation), approximately at same height as coronoid process.

TAXONOMIC COMPARISONS: Neacomys vossi differs from N. dubosti in dorsal pelage color (brown sprinkled with orange and/or black versus dark brown finely sprinkled with orange in N. dubosti ), and by its narrower interorbital region, and globular auditory bullae (the bullae are usually flask shaped in N. dubosti ).

Neacomys vossi differs from N. xingu in dorsal pelage color (brown sprinkled with orange and/or black versus orange-brown sprinkled with black in N. xingu ), larger sphenopalatine foramen, and an M1 anteroloph that is usually distinct (versus fused in N. xingu ).

Karyotypically, Neacomys vossi differs from other species in the Dubosti Group by having a diploid chromosome complement of 58 (versus 2 n = 64 in N. dubosti and 2 n = 64 in “species 2”), an FN of 68 autosomal arms (versus FN = 70 in N. marajoara, FN = 64 in N. xingu , and FN = 66 in “species 2”), and submetacentric sex chromosomes (at least one of the sex chromosomes is acrocentric in N. dubosti and “species 2”) DISTRIBUTION: Neacomys vossi has been collected on the right bank of the upper and middle Tapajós River and on the left bank of lower Xingu (fig. 5). According to our records, the species appears to be endemic to the Tapajós center of endemism ( Silva et al., 2005). ETYMOLOGY: Named in honor of Robert S. Voss ( fig. 10 ), curator of mammals at the American Museum of Natural History , New York, for his extensive contributions to our knowledge of Neotropical mammals, especially the taxonomy of Neacomys in northeastern Amazonia.

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FIELD NOTES: Among the specimens we examined for which trapping information is available, all 17 were captured in pitfall traps, two (UFPA 1277 and 1284) in upland (terra firme) forests and three (UFPA 1444, 1487, and 1583) in primary forest of unknown character.

REMARKS: Neacomys vossi was previously reported in the literature as “ Neacomys sp. A” by Oliveira da Silva et al. (2017, 2019).

Figures

FIG. 8. Dorsal and ventral views of the skin of Neacomys vossi (UFPA 1583, holotype).

FIG. 9. Dorsal, ventral, lateral cranial views and lateral view of mandible of Neacomys vossi (UFPA 1583, holotype).

FIG. 10. Robert S. Voss in the field (Venezuela, 1979; photo by Paul Kaarakka).