Systematics of Neotropical Spiny Mice, Genus Neacomys Thomas, 1900 (Rodentia: Cricetidae), from Southeastern Amazonia, with Descriptions of Three New Species Author Semedo, Thiago Borges Fernandes Maria Nazareth Ferreira Da Silva, & Mario Da Silva Nunes, & Programa de Pós-graduação em Zoologia, Instituto de Biociências, Universidade Federal de Mato Grosso (UFMT), Cuiabá, Brazil. & Maria Nazareth Ferreira Da Silva, & Instituto Nacional de Pesquisa do Pantanal (INPP), Museu Paraense Emílio Goeldi (MPEG) - Programa de Capacitação Institucional, Cuiabá, Brazil. Author Silva, Maria Nazareth Ferreira Da Eliécer E. Gutiérrez, & Coleção de Mamíferos, Instituto Nacional de Pesquisas da Amazônia (INPA), Manaus, Brazil. Author Gutiérrez, Eliécer E. Daniela Cristina Ferreira, & Programa de Pós-Graduação em Biodiversidade Animal, Centro de Ciências Naturais e Exatas, Universidade Federal de Santa Maria (UFSM), Santa Maria, Brazil. Author Ferreira, Daniela Cristina Maria Nazareth Ferreira Da Silva, & Mario Da Silva Nunes, & Programa de Pós-graduação em Zoologia, Instituto de Biociências, Universidade Federal de Mato Grosso (UFMT), Cuiabá, Brazil. Author Nunes, Mario Da Silva Ana Cristina Mendes-Oliveira, & Laboratório de Evolução e Genética Animal (LEGAL), Departamento de Genética, Universidade Federal do Amazonas (UFAM), Manaus, Brazil. Author Mendes-Oliveira, Ana Cristina Izeni Pires Farias, & Instituto de Ciências Biológicas - LABEV, Universidade Federal do Pará (UFPA), Belém, Brazil. Author Farias, Izeni Pires Ana Cristina Mendes-Oliveira, & Laboratório de Evolução e Genética Animal (LEGAL), Departamento de Genética, Universidade Federal do Amazonas (UFAM), Manaus, Brazil. Author Rossi, Rogério Vieira Maria Nazareth Ferreira Da Silva, & Mario Da Silva Nunes, & Programa de Pós-graduação em Zoologia, Instituto de Biociências, Universidade Federal de Mato Grosso (UFMT), Cuiabá, Brazil. text American Museum Novitates 2020 2020-09-05 2020 3958 1 43 http://dx.doi.org/10.1206/3958.1 journal article 5835 10.1206/3958.1 b21652c7-9d47-402f-bf45-a524a3181d21 0003-0082 5056873 Neacomys marajoara , new species Marajoara Spiny Mouse Figures 4 , 7 HOLOTYPE : The holotype ( MPEG 40432 ) is an adult male (age class 3), collected on 19 January 2009 , by R . V . Rossi (field number MAJ 23 ; fig. 4) in a pitfall trap . The specimen consists of a stuffed skin (missing the tip of the tail), skull, and skeleton; a tissue sample of this specimen is preserved in ethanol, and a partial cytochrome b sequence that we obtained from it has been deposited in Genbank with accession number MT 462070 . TYPE LOCALITY : Tauari Farm , municipality of Chaves , Marajó Island , state of Pará , Brazil ( 0°39′S , 50°11′W , figs. 5, 6) . DIAGNOSIS: Neacomys marajoara is a small species (table 3) that differs from congeneric taxa by the following combination of craniodental traits: skull delicate; interorbital region relatively broad; nasal bones straight anteriorly; supraorbital margins slightly convergent anteriorly; subsquamosal fenestra large (almost half the size of the postglenoid foramen on each side of the skull); paraoccipital processes separated from the auditory bullae; sphenopalatine foramen large; carotid circulation usually pattern 2 (sensu Voss, 1988 ); maxillary part of incisive septum (between the incisive foramina) narrow; M1 usually with flat and undivided anterocone; and M1 anteroloph usually fused with anterolabial conule. FIG. 3. Scatter plots of PC1 (horizontal axis) and PC2 (vertical axis) for pairwise analyses of craniodental measurement data for species in the Dubosti Group of Neacomys . In each plot, species are represented by minimum convex polygons that enclose all points in the plane of PC1 and PC2. A, N . dubosti (dub) versus N . marajoara (mar); B, N . dubosti versus N . vossi (vos); C, N . dubosti versus N . xingu (xin); D, N . marajoara versus N . vossi ; E, N . marajoara versus N . xingu ; F, N . vossi versus N . xingu . FIG. 4. The holotype of Neacomys marajoara , (MPEG 40432) in life. Photo by Rogério V. Rossi. MORPHOLOGICAL DESCRIPTION: Dorsal pelage dark brown finely sprinkled with orange (fig. 4); ventral pelage varying from pure white to yellowish white, separated from the dorsal pelage by a 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; postauricular hairs gray based with orange tips, forming an orange tuft behind each pinna. Ungual tufts white, longer than claws in most specimens examined (except MPEG 40435 and MPEG 40446, in which ungual tufts are as long as the claws); fore- and hind feet covered dorsally with buffy-cream hairs; hind feet narrow and elongate with small interdigital membranes present. Tail about the same length as head and body, bicolored, and covered by short, spiny, and clearly visible hairs; white hairs present on ventral caudal surface from base to midlength; tail tip with very short ( 1 mm ) terminal tuft; caudal scales small, arranged in annular series; each caudal scale with three subequal hairs inserted along its posterior margin. FIG. 5. Collection localities of specimens of the Dubosti Group of Neacomys examined in the present study. Numbers are keyed to entries in our gazetteer (appendix 1). Skull small and delicate in dorsal view (fig. 7), with straight anterior nasal margins, notably broad rostrum, and shallow zygomatic notches; posterior nasal terminus usually slightly pointed, extending beyond maxillary-frontal suture; premaxillaries terminating anterior to nasals; lacrimal bone small and visible in dorsal view, usually in broad contact with frontal bones; supraorbital margins slightly convergent anteriorly; interorbital region relatively broad; supraorbital beads developed as projecting shelves; lateral expansion of the parietal restricted to the dorsal cranial surface. Incisive foramina small and usually teardrop shaped, not extending posteriorly to level of M1s; maxillary portion of incisive septum (dividing the left and right foramina) narrow. Zygomatic plate narrow. Palate with two posterolateral pits on each side. Auditory bullae small and globular, with short and narrow eustachian tubes; periotic bone extends anteriorly to internal carotid canal (except MPEG 40435, MPEG 40443, and MPEG 40439, in which the periotic does not reach the internal carotid canal), but does not enter the canal. Subsquamosal fenestra large (almost half the size of the postglenoid foramen); hamular process of the squamosal long. Paraoccipital process narrow and small and separated from the auditory bullae. Sphenopalatine foramen large; alisphenoid strut absent; carotid circulation pattern usually derived 7 (pattern 2, as identified by the presence of a large stapedial foramen and a large posterior opening of the alisphenoid canal, and by the absence of a squamosalalisphenoid groove and a sphenofrontal foramen; Voss, 1988 ). FIG. 6. Habitat of Neacomys marajoara at Tauari Farm, municipality of Chaves, Marajó Island, state of Pará, Brazil. Photo by Rogério V. Rossi. First upper molar (M1) usually with broad, flat, and undivided anterocone; anteroloph usually fused with anterolabial conule (such that the anteroflexus is not distinguishable); M3 small; labial cusps (paracone and metacone) usually smaller than lingual cusps (protocone and hypocone); m1 anterocone undivided. Mandible with mental foramen opening laterally; capsular process of lower incisor alveolus present, but indistinct (reduced to a slight rounded elevation), approximately at same height as coronoid process. KARYOTYPES: Karyotypes of specimens from the type locality were obtained by Silva et al. (2015) , and karyotypes from specimens collected elsewhere on Marajó Island were obtained by Oliveira da Silva et al. (2019) , who described a chromosomal complement of 2 n = 58 and a fundamental number (FN) = 70 (table 5). 7 Most specimens of Neacomys marajoara (seven out of nine) exhibit carotid circulation pattern 2, but one specimen (MPEG 40446) exhibits circulatory pattern 1, and another (MPEG 40431) exhibits both patterns (on opposite sides of the skull). FIG. 7. Dorsal, ventral, and lateral cranial views and lateral view of mandible of Neacomys marajoara (MPEG 40432, holotype). TAXONOMIC COMPARISONS: Neacomys marajoara differs from N. dubosti in dorsal pelage color (dark brown finely sprinkled with orange versus light to dark brown finely sprinkled with orange in N. dubosti ), and by its bicolored tail (the tail is usually unicolored in N. dubosti ), narrower interorbital region, teardrop-shaped incisive foramina (the lateral margins of the incisive foramina are usually subparallel in N. dubosti ), globular auditory bullae (the bullae are usually flask-shaped in N. dubosti ), and carotid circulation usually pattern 2 (versus pattern 1 in N. dubosti ). TABLE 4. Geographic and morphological comparisons among members of the Dubosti Group of Neacomys .

dubosti	xingu	marajoara	vossi
Distribution	NE Amazonia	SE Amazonia	SE Amazonia	SE Amazonia
Dorsal pelage	light to dark brown finely sprinkled with orange	orange-brown sprinkled with black	dark brown finely sprinkled with orange	brown sprinkled with orange and/or black
Ventral pelage	pure white to buffy white	pure white to buffy white	pure white to yellow- ish white	pure white to buffy white
Tail	usually unicolored	usually unicolored	bicolored	usually slightly bicolored
Nasal bones	–	expanded anteriorly	straight anteriorly	expanded anteriorly
Interorbital region	broad	narrow	relatively broad	narrow
Paraoccipital process	–	usually separated from auditory bullae	separated from audi- tory bullae	close to the auditory bullae
Subsquamosal fenes- trae	–	small	large	usually small
Sphenopalatine fora- men	–	small	large	large
Lateral expansion of parietal	restricted	slightly expanded to restricted	restricted	slightly expanded to restricted
Carotid circulation	pattern 1	usually pattern 1a	usually pattern 2b	pattern 1
Incisive foramina	small and usually subparallel	small and subparallel	small and usually teardrop shaped	small and subparallel
Maxillary septum of incisive foramina	–	wide	narrow	usually wide
Zygomatic plate	narrow	narrow to broad	narrow	narrow
Auditory bullae	usually flask-shaped	usually globular	globular	globular
M1 anteroloph	–	fused	fused or distinct	usually distinct

a We found variation in this character, please see Neacomys xingu description. b We found variation in this character, please see Neacomys marajoara description. Neacomys marajoara differs from N. xingu in dorsal pelage color (dark brown finely sprinkled with orange versus orange-brown sprinkled with black in N. xingu ), and by its bicolored tail (the tail is usually unicolored in N. xingu ), anteriorly straight (versus anteriorly expanded) nasal bones, broader interorbital region, narrower maxillary septum of the incisive foramina, larger subsquamosal fenestrae, and carotid circulation usually pattern 2 (versus usually pattern 1). Neacomys marajoara differs from N. vossi in dorsal pelage color (dark brown finely sprinkled with orange versus brown sprinkled with orange and/or black in N. vossi ), and by its anteriorly straight (versus anteriorly expanded) nasal bones, broader interorbital region, paraoccipital processes separated from the auditory bullae (versus processes close to the auditory bullae), larger subsquamosal fenestrae, carotid circulation usually pattern 2 (versus pattern 1), and narrower maxillary septum of the incisive foramina. Karyotypically, Neacomys marajoara differs from other species in the Dubosti Group by having a diploid chromosomal complement of 58 (versus 2 n = 64 in N. dubosti ; table 5), a uniquely large FN of 70 autosomal arms (versus FN = 64–68 in other group members), and submetacentric sex chromosomes (at least one of the sex chromosomes is acrocentric in N. dubosti and “species 2”). DISTRIBUTION: Neacomys marajoara has been recorded only on Marajó Island, state of Pará, Brazil (fig. 5). ETYMOLOGY: The specific epithet marajoara is to be treated as a noun in apposition. It is derived from Tupi Guarani (a language family that comprises many different indigenous Amazonian dialects) and denotes a native of Marajó Island (the type locality). FIELD NOTES : Of the nine specimens for which trapping information is available, eight were captured in pitfall traps and one was taken in a Sherman trap placed on the ground. One paratype ( MPEG 40435 ) was pregnant with three fetuses. REMARKS: Neacomys marajoara was previously reported in the literature as “ Neacomys sp.” (in part) by Silva at al. (2015) and as “ Neacomys sp. D” by Oliveira da Silva et al. (2019) .