Oecomys matogrossensis, Saldanha & Rossi, 2021

Saldanha, Juliane & Rossi, Rogério Vieira, 2021, Integrative analysis supports a new species of the Oecomys catherinae complex (Rodentia, Cricetidae) from Amazonia, Journal of Mammalogy (J. Mammal.) 102 (1), pp. 69-89 : 76-85

Oecomys matogrossensis sp. nov.

Figures 5–8 ; Tables 2 and 3

Oecomys sp. 1 : Di-Nizo et al. 2017:843.

Oecomys catherinae western clade: Suárez-Villota et al. 2018:190.

Oecomys aff. catherinae: Saldanha et al. 2019:44 .

Oecomys catherinae western clade: Brandão et al. 2019:266.

Holotype.— UFMT 4118, adult, male, preserved in dry skin, skull, and complete postcranial skeleton. Collected by Rogério Vieira Rossi (field number RVR 89) on 12 May 2014. Hologenotypes Cytb and i7-fgb are deposited in GenBank (accession number MK874365 and MT978188 , respectively).

Measurements (in mm) and body mass of the holotype.— TL = 226, HBL = 106, T = 120, E = 17, HFL = 26, ONL = 28.90, CIL = 25.86, BH = 8.36, CZL = 20.51, ZL = 13.35, LD = 6.71, BZP = 2.96, BN = 3.74, LN = 11.15, LR = 9.08, BR = 4.44, LIB = 5.20, OL = 10.39, ZB = 14.98, LIP = 3.81, BIP = 9.58, BIF = 2.12, LIF = 3.94, BRP = 4.58, LPB = 5.95, MB = 10.32, BOC = 5.99, BB = 4.38, BI = 1.51, BM 1 = 1.32, CLM = 4.77, Bm1 = 1.22, CLLM = 4.97, LLD = 2.89, LCIB = 14.64, MH = 6.67, body mass 33 g.

Paratypes.— UFMT 1773, adult, female, preserved as skin and skull. Collected by T. S. Santos-Júnior on 29 October 2009 (field number UTP 159 ) from the Teles Pires Hydroelectric Power Plant, Paranaíta municipality, Mato Grosso state, coordinates: 9°29′06″S, 56°28′19″W, left bank of the Teles Pires River, tributary of the Tapajós River. Measurements: HBL = 105.82 mm, T = 122.05 mm, E = 15.72 mm, HFL = 25.52 mm, weight 34 g. UFMT 1680, adult, male, preserved in skin and skull. Collected by T. S. Santos-Júnior on 18 April 2009 (field number UTP 02 ) at the Teles Pires Hydroelectric Power Plant , Paranaíta municipality, Mato Grosso state, coordinates: 9°29′10″S, 56°28′19″W, left bank of the Teles Pires River , tributary of the Tapajós River . Measurements: HBL = 125 mm, T = 132 mm, E = 17 mm, HFL = 24 mm, weight 22 g .

Type locality.— Estância Santa Clara, Alta Floresta municipality, left bank of the Teles Pires River , tributary of the Tapajós River , Mato Grosso state, coordinates: 10°00′25″S, 56°02′17″W ( GPS coordinates taken at the trap site) .

Additional material.— Twenty specimens from Mato Grosso state, Brazil: skin of MSF 1878 , female (9°46′12″S, 56°10′15.6″W, Alta Floresta); skin and skull of MZUSP 29531 , female (10°10′01″S, 59°27′W, Aripuanã); skins of MSF 1406 , female; MSF 1407 , 1411 , males (11°34′58″S, 55°10′01″W, Cáceres); skin and skull of MZUSP 35543 , male (11°34′58″S, 55°10′01″W, Cláudia); skin and skull of MZUSP 29516 , female (13°04′58″S, 53°16′58″W, Gaúcha do Norte); skin and skull of MZUSP 35537 , female (10°19′01″S, 58°28′58″W, Juruena); skin and skull of UFMT 931, female (12°51′S, 58°56′W, Juruena); skins and skulls of UFMT 1772, 1774, 1806 ,

a External measurements were transcribed from original skin labels.

females (9°29′06″S, 56°28′19″W, Paranaíta); skins and skulls of AC 207 , 230 , males; AC 255 , 266 , females (15°04′45.9″S, 56°33′15.7″W, Rosário Oeste); skins of RFO 013, female; RFO 027, 029, 040, males (15°10′33.6″S, 59°59′38.4″W, Vila Bela da Santíssima Trindade ). Four specimens from Pará state, Brazil: skins and skulls of UFMT 1775, 1776, males; UFMT 1686, UFMT 1690, females (9°18′40″S, 56°46′05″W, Jacareacanga). One specimen from Rondônia state, Brazil: skin and skull of MPEG 34224 (12°43′S, 60°7′W, Vilhena) .

Diagnosis.— Soft, long dark reddish-brown dorsal fur (length: 7–11 mm); ventral fur dark cream, composed of gray-based hairs throughout the venter and self-dark cream hairs on areas of the throat, neck, forelimbs, and genitalia; caudal tuft absent, but hairs exceed tail tip (<1 mm). Rostrum narrow and moderately long; posterior margin of the nasals V- or U-shaped, surpassing or aligned to the posterior portion of the maxillary– frontal suture, and premaxillaries terminating anterior to the nasals; supraorbital crest moderately developed, similar to the temporal crest; parietal slightly expanded below the lateral edges of the dorsum of the braincase; hamular process narrow; subsquamosal fenestra present; alisphenoid strut usually absent; complete stapedial circulation (pattern 1— Voss 1988); and anterior cingulum present on the first upper molar.

Morphological description.— Oecomys matogrossensis is characterized by medium size ( HBL: 85–135 mm), tail longer (TL: 106–160 mm) than combined head and body (i.e., tail from 104% to 148% of HBL). Soft and abundant pelage, with hairs varying from 7 to 11 mm in length. Dorsal hairs gray-based with terminal tips dark reddish-brown, mixed with some gray-based and dark brown-tipped hairs ( Fig. 5A ). Flanks lighter than the dorsum, with poorly marked lateral/ventral transition. Venter dark cream with gray-based hairs throughout the belly, except on the throat, neck, forelimbs, and genitalia, where the hairs are self-dark cream ( Fig. 5A ). Hairs shortest and lightest in the rostrum. Mystacial vibrissae abundant and dark brown, with the longest surpassing the posterior edge of the pinnae. Ears light brown at the base and dark brown at the end, with orange and some brown hairs on the outer and inner pinnae surfaces. Manus and pes dorsally covered with white hairs, mixed with brown hairs in the median portion; on the manus, the brown fur covers the arms toward the body. Ungual hairs white, abundant and long, surpassing the claws, except for digit I. Distal end of digit I surpassing the second interdigital pad. Plantar surface with small scales between pads, four developed interdigital pads equal in size and closely positioned, a hypothenar pad smaller than the interdigital pads, and a developed and long thenar pad that extends proximally. Tail completely brown, but slightly bicolor on the proximal portion. Caudal scales with three hairs, with the longest hair exceeding two scale rows in length. Caudal tuft absent, but hairs exceed tail tip about 1 mm in length. Four mammary pairs distributed as follows: one pectoral, one postaxial, one abdominal, and one inguinal (Voss and Carleton 1993).

Skull small when compared to the other lineages of the O. catherinae complex s.s. ( Table 2), and medium compared to other congeners. Rostrum narrow and moderately long. Anterior margins of the nasal bones rounded, surpassing the anterior portion of premaxillary bones; posterior margin of nasals V- or U-shaped, aligned or extending beyond the posterior portion of the maxillary–frontal sutures ( Figs. 6 and 7A ), and premaxillaries terminating anterior to the nasals. Poorly developed zygomatic notch, but dorsally visible. Lacrimal in contact with maxillary and frontal bones. Interorbital region convergent anteriorly, with narrow median region; supraorbital ridges moderately developed, as well as the temporal ridges ( Figs. 6 and 7C ). Rounded cranial vault. Interparietal wider than posterior border of frontals, but not contacting the squamosal. Exoccipital crests absent or poorly developed in dorsal view ( Fig. 6 ).

Zygomatic plate broad, slightly projected anteriorly to the maxillary root of the zygomatic, and posterior margin positioned anteriorly to M1. Jugals small, their maxillary and squamosal processes not overlapping. Squamosal root of the zygomatic arch expanded laterally. Parietal slightly expanded below the lateral edges of the dorsum of the braincase (greater expansion in UFMT 1680; Fig. 7E ). Hamular process narrow; subsquamosal fenestra small or medium, never larger than the postglenoid foramen ( Fig. 7E ). Lambdoidal crests poorly developed. Mastoid with small fenestra that does not contact the edge of the exoccipital, or with a larger fenestra that reaches the exoccipital edge.

Incisive foramina small, drop- or oval-shaped, with posterior margin not reaching the first molars. Palate long and wide (sensu Hershkovitz 1962) with conspicuous posterolateral palatal pits located in deep palatal depressions. Mesopterygoid fossa U-shaped, aligned with the posterior margin of the maxillary; roof of mesopterygoid fossa fully ossified or with small perforations. Parapterygoid fossa dorsally excavated, but not reaching the mesopterygoid level. Alisphenoid strut absent (except in MPEG 34224 and UNEMAT – AC 266). Primitive pattern of stapedial circulation (pattern 1 of Voss 1988), with stapedial foramen and posterior opening of the alisphenoid canal developed, and presence of squamosal-alisphenoid groove and sphenofrontal foramen. Tegmen tympani not contacting the squamosal, or contacting the squamosal punctually. Small ectotympanic bulla; periotic slightly exposed and usually reaching the carotid canal. Eustachian tube narrow and short, with edge parallel to the basioccipital suture ( Fig. 6 ).

Mandible robust, with mental foramina dorsally located in the diastema, anterior to m1. Upper and lower masseteric ridges converge and fuse only in the anterior portion, below the anterior portion of m1. Capsular process lower incisor small and conspicuous. Coronoid process small and pointed. Angular process short. Condyloid process elongated ( Fig. 6 ).

Upper incisors opisthodont ungrooved, with yellow-orange anterior enamel surfaces; upper molar rows parallel arranged in opposite labial-lingual pairs. Molars are pentalophodont and brachyodont. Upper first molar (M1): anterior cingulum (i.e., stylar shelf on the anterior border of the procingulum, positioned anteriorly to the anterocone) present (refer to Pires et al. 2016 for description and comments on this structure); procingulum with a central fossete; anterocone not divided by anteromedian flexus (anteromedian flexus present in UFMT 1773, dividing the procingulum into anterolabial and anterolingual conules); anteroloph present and connected to the anterocone and paracone by parastyle; paracone connected to protocone by median mure, with long paraflex; protocone connected to the anterior mure and separated from the anterocone by protoflexus; paralophule present in paracone and connected to the mesoloph; posteroloph fused to metacone, with presence of fossetus derived from the posteroflexus; labial and lingual accessory roots absent; labial and lingual cingula absent ( Fig. 8 ). Upper second molar (M2): anteroloph present; anterolingual cingulum present, but poorly developed in the anterior portion of the protocone; lingual cingulum present; paralophule connecting paracone to mesoloph; posteroloph present ( Fig. 8 ). Upper third molar (M3): smaller than the half of M1 and larger than half of M2; mesoloph and short posteroloph present; hypocone slightly reduced with respect to protocone and separated from the protocone by hypoflexus; reduced metacone ( Fig. 8 ).

Lower first molar (m1): anteromedian flexid present, dividing procingulum into anterolabial and anterolingual conulids; procingulum with anteromedian fossetid well-developed. Anterolabial cingulum connected to a well-developed protostylid; ectolophid present; metaconid with metalophulid connected to mesolophid that is fused in its distal portion to the entoconid; posterolophid long and fused by wear to the entoconid; hypolophulid present ( Fig. 8 ). Lower second molar (m2): anterolabial cingulum present and well-developed; entoconid small; small ectolophid and ectostylid present; posterolophid connected to the entoconid ( Fig. 8 ). Lower third molar (m3): smaller than half of m1 and same length as m2; anterolabial cingulum present; small ectolophid and ectostylid present; posterolophid probably present and connected to the entoconid, that is reduced ( Fig. 8 ).

Karyotype.— Specimens of the western clade exhibited 2n = 54, FN = 54, with a small submetacentric pair (pair 1) and all the other autosomes acrocentric (pairs 2–26). The X chromosome is large and submetacentric, with a short heterochromatic arm, and the Y chromosome is medium sized, metacentric and entirely heterochromatic (see Suárez-Villota et al. 2018).

Etymology.— The specific name is a geographical reference to the Brazilian state of Mato Grosso, where the holotype was collected and where most of the species distribution is located.

Distribution and sympatry.— Oecomys matogrossensis occurs in southern Amazonia; the species’ distributional area extends from Jacareacanga (on the right bank of the Teles Pires River in the extreme southwest of Pará state) southward to Cáceres (in the extreme southwest of Mato Grosso state),

and the premaxillaries aligned to the posterior margin of the nasals in O. catherinae ( BNMH 9.11.19.24); (C) supraorbital and temporal crests poorly developed in O. matogrossensis ; (D) supraorbital crest dorsolaterally expanded in O. catherinae northern lineage ( MPEG 39899), being more developed than temporal crest; (E) subsquamosal fenestra present, always smaller than postglenoid foramen, and parietal slightly expanded below the lateral edges of the dorsum of the braincase (white arrow) in O. matogrossensis ; (F) subsquamosal fenestra ossified and parietal deeply expanded onto the lateral surface of the braincase (white arrow) in O. catherinae northern lineage ( MPEG 39899). exo, exoccipital; fro, frontal; ip, interparietal; mas, mastoid; max, maxillary; nas, nasal; par, parietal; pgf, postglenoid foramen; pre, premaxillary; soc, supraorbital crest; sq, squamosal; ssf, subsquamosal fenestra; tc, temporal crest.

and from Vilhena (Rondônia state) and Aripuanã (between the Juruena and Aripuanã rivers, in Mato Grosso state) eastward to Gaúcha do Norte (on the left bank of the Xingu River, Mato Grosso state). The species occurs in sympatry with O. cleberi and the westernmost lineage of O. catherinae complex s.s. on the west margin of the Juruena River, Mato Grosso state; and with O. bicolor , O. paricola , and O. roberti , in the municipality of Cláudia, Mato Grosso state ( Suárez-Villota et al. 2018; Saldanha et al. 2019).

Habitat information.— Oecomys matogrossensis was collected in forested habitats from the southern Amazonia, particularly from the Amazonia–Cerrado transition zones, and the edge of the Pantanal biome. Also, two collecting points are located in the Cerrado biome (Localities 6 and 9; Fig. 1 ), but habitat information was not available on the vouchers’ labels.

Comparisons.— Oecomys matogrossensis is distinguished from O. catherinae complex s.s. lineages by exhibiting smaller body size ( Tables 2 and 3; Fig. 5 ) and short dorsal pelage (7–11 mm) with dark reddish-brown coloration, versus long dorsal pelage (9–15 mm) with reddish-brown color. In addition, the new species has a darker cream ventral pelage when compared to the central and eastern lineages ( Fig. 5 ; Table 3).

The skull is smaller in O. matogrossensis than in O. catherinae complex s.s. lineages ( Table 2). The rostrum is narrow and moderately long in the new species, but is wide and long in eastern and westernmost lineages of O. catherinae complex s.s., wide and short in the central lineage, and narrow and short in northern lineage ( Table 3). The posterior margin of the nasals extends beyond the posterior portion of the maxillary–frontal suture in O. matogrossensis ( Fig. 7A ), contrasting with the O. catherinae complex s.s. lineages, whose posterior margin of the nasals does not reach or is aligned to the posterior part of the maxillary–frontal suture ( Fig. 7B ). In O. matogrossensis , the interorbital region is narrower compared to the eastern, westernmost, and northern lineages of O. catherinae complex s.s. Moreover, the supraorbital and temporal crests are moderately developed in the new species ( Fig. 7C ), whereas the supraorbital crest is dorsolaterally and distinctly more developed than the temporal crest in the O. catherinae complex s.s. lineages ( Fig. 7D ). The subsquamosal fenestra always is present in O. matogrossensis ( Fig. 7E ), while it is reduced in the eastern and westernmost lineages of O. catherinae complex s.s., and fully ossified in the central and northern lineages ( Fig. 7F ). The parietal is slightly expanded below the lateral edges of the dorsum of the braincase in O. matogrossensis ( Fig. 7E ), while it is deeply expanded onto the lateral surface of the braincase in the O. catherinae complex s.s. lineages ( Fig. 7F ).

Because O. catherinae is similar externally to O. rex in pelage color and texture, we provide comparisons of O. matogrossensis with the latter species. Externally, the new species differs from O. rex by exhibiting shorter dorsal fur (7–11 mm versus 9–14 mm in O. rex ) and lacking a caudal tuft (versus a small tuft present in O. rex ). Cranially, the skull is smaller in O. matogrossensis (mean 28.9 mm) than in O. rex (mean 31.05 ± 3.10 mm; n = 8); the supraorbital and temporal crests are moderately developed in the former species (versus strongly developed supraorbital crests, joining in a prominent temporal crest in O. rex ); and the subsquamosal fenestra always is open in O. matogrossensis , while it is reduced or absent in O. rex .

Oecomys matogrossensis can be distinguished from other congeneric sympatric species, such as O. bicolor , O. cleberi , O. roberti , and O. paricola , by exhibiting medium body and cranial size (versus smaller body and cranial size in O. bicolor and O. cleberi ); dark reddish-brown dorsal coloration (versus orangish-brown in O. bicolor and O. cleberi ; reddish- to orangish-brown in O. roberti ; and reddish-brown in O. paricola ); dark cream ventral coloration (versus totally white or cream venter in O. bicolor and O. cleberi ; fully white or a white ventral midline with gray-based lateral bands in O. roberti ); and absence of caudal tuft (versus presence of caudal tuft in O. bicolor , O. cleberi , and O. paricola ). Detailed descriptions of the mentioned species can be found in Rocha et al. (2012), Carleton and Musser (2015), and Rocha et al. (2018).

Figures

Fig. 5.—Dorsal view (above) and ventral view (below) of: (A) the holotype of Oecomys matogrossensis sp. nov. (UFMT 4118), and specimens of the Oecomys catherinae complex lineages: (B) eastern (MN 10748), (C) central (PCH 4077), (D) westernmost (APC 292), and (E) northern (MZUSP 35535 above, and MZUSP 29532 below). Scale: 20 mm.

Fig. 6.—Dorsal, ventral, and lateral views of skull and lateral view of mandible of the holotype (UFMT 4118) of Oecomys matogrossensis sp. nov. from Estância Santa Clara, Alta Floresta, Mato Grosso state, Brazil. Scale: 5 mm.

Fig. 7.—Anatomical traits that differentiate Oecomys matogrossensis sp. nov from the O. catherinae complex lineages: (A) posterior nasal terminus (shorter dashed line) surpassing the maxillary–frontal suture (longer dashed line) and the premaxillaries terminating anterior to the nasals in O. matogrossensis (UFMT 4118); (B) posterior nasal terminus (shorter dashed line) anterior to the maxillary–frontal suture (longer dashed line)

Fig. 8.—Paratype of Oecomys matogrossensis sp. nov. from Teles Pires Hydroelectric Power Plant, Paranaíta municipality, Mato Grosso state, Brazil (UFMT 1680): upper molar series (left) and lower molar series (right). ac, anterior cingulum.

Fig. 1.—Map of samples of the Oecomys catherinae complex s.l. included in this study, with discrimination of the lineages recognized for the complex. Stars indicate the type localities of Oecomys matogrossensis sp. nov. (1; western lineage), Oecomys catherinae (51), and Oryzomys concolor bahiensis (39).