Oligoryzomys mattogrossae (J.A. Allen, 1916)

Weksler, Marcelo, Lemos, Elba M. S., D'Andrea, Paulo Sérgio & Bonvicino, Cibele Rodrigues, 2017, The taxonomic status of Oligoryzomys mattogrossae (Allen 1916) (Rodentia: Cricetidae: Sigmodontinae), reservoir of Anajatuba Hantavirus, American Museum Novitates 2017 (3880), pp. 1-32 : 17-21

Oligoryzomys mattogrossae (J.A. Allen, 1916)

Figures 2 and 3 HOLOTYPE: AMNH37542 adult male; measurements of holotype in mm (see Material and Methods for acronyms): TL = 210, HBL = 95, T = 115, PB = 4.08, LIF = 4.48, BIF = 1.61, LM

= 3.30, BM1 = 0.97, M1M = 4.50, BRO = 4.56, LIB = 3.45, ORL = 8.05, BZP = 2.4. The holotype corresponds to an old adult individual, i.e., with advanced wear of molars and large skull measurements (table 3), and has a severely damaged skull.

TYPE LOCALITY: Brazil, Mato Grosso state, Rio Papagaio, Utiariti .

GEOGRAPHIC DISTRIBUTION: Oligoryzomys mattogrossae occurs throughout the Cerrado and Caatinga biomes of central and northeastern Brazil and Paraguay, as well as in the Cerrado-Amazonia ecotone between Mato Grosso and Pará states, and between the Pantanal region of Corumbá in Mato Grosso do Sul state (fig. 1). In Brazil, the species has been recently reported in the states of Mato Grosso do Sul (Carmingnotto et al., 2014), São Paulo ( Vivo et al., 2011), Tocantins ( Di-Nizo et al., 2015), Pará ( Rocha et al., 2011), and Bahia ( Pereira and Geise, 2009). Therefore, O. mattogrossae is found in the Brazilian Caatinga (Bahia, Alagoas, Pernambuco, Paraíba states) and Cerrado (Distrito Federal, São Paulo, Minas Gerais, Mato Grosso, Mato Grosso do Sul, Goiás, Tocantins, Bahia, and Maranhão states). O. mattogrossae also possibly occurs in Bolivia (e.g., Santa Cruz specimens listed as O. microtis in Olds and Anderson, 1987, and Anderson, 1997), but voucher material still needs to be analyzed to confirm identification. See appendix 1 for specific localities and examined material.

EMENDED DIAGNOSIS: A small-sized Oligoryzomys species (adult HBL <96 mm in average) characterized by the combination of the following morphological characteristics: (1) rufous tone in dorsum, especially on the rump, (2) underparts light ochraceous buff instead of grayish white, (3) dorsal and ventral coloration without a well-defined limit, (4) position of posterolateral pits lateral to the mesopterygoid fossa; and (5) posterior extension of palatal bridge smaller than the size of M3. In addition, all known karyotyped specimens share the same diploid number of 62 and fundamental autosome number of 64.

DESCRIPTION: Adult dorsal pelage grizzled yellowish, between Antique Brown and Dresden Brown ( Ridgway, 1912), composed of long guard hairs and slightly shorter overhairs with a subapical brown-yellowish band. Lateral color lighter than in dorsum and without a clearly defined limit with the yellowish ventral pelage. Ventral hair upper half yellowish, gray at base. Short tufts of white ungual hair at base of claws on dII–dV. Tail longer than combined length of head and body, sparsely haired, and covered with more or less conspicuous epidermal scales, lacking a long tuft of terminal hairs and weakly bicolored, dorsal surface dark gray and ventral surface light gray. Superciliary, genal, and mystacial vibrissae not extending beyond ears. Presence of eight mammae in inguinal, abdominal, postaxial, and pectoral positions.

Delicate skull, narrow rostrum, but slightly wider than interorbital constriction. Interorbital region hourglass shaped. Braincase without supraorbital and postorbital ridges and with weakly developed lambdoidal ridge. Interparietal bone as broad as anterior half of parietal. Relatively large zygomatic plate with zygomatic notch intermediate between deep and shallow. Jugal bone absent, resulting in zygomatic process of squamosal in contact with the zygomatic process of maxillary. Incisive foramina with almost parallel margins, the posterior borders reaching or almost reaching the plane of alveolus of the first upper molars, but never extending posteriorly. Palate with a single large or two posterolateral palatal pits not recessed in palatine fossa, lateral to mesopterygoid fossa. Palatal bridge broad and long. Bony roof of mesopterygoid fossa perforated by large sphenopalatine vacuities. Width of parapterygoid plate slightly greater than width of mesopterygoid fossa. Alisphenoid strut absent (buccinator-masticatory foramen and accessory foramen ovale confluent), alisphenoid canal with large anterior opening. Stapedial foramen and the posterior opening of the alisphenoid canal large, but squamosal-alisphenoid groove and sphenofrontal foramen absent (= carotid circulatory pattern 2 of Voss, 1988). Posterior suspensory process of the squamosal absent. Large subsquamosal fenestra, slightly smaller than postglenoid foramen. Periotic exposed posteromedially between ectotympanic and basioccipital, not reaching the carotid canal. Mastoid perforated by conspicuous posterodorsal fenestra. In mandible, capsular process of lower incisor alveolus well developed in most adults; superior and inferior masseteric ridges converging anteriorly as open chevron below m1.

Upper and lower incisors opisthodont; molars pentalophodont. Superior molar rows parallel. Procingulum of first upper molar (M1) with anteromedian flexus only in young animals, specimens with moderate wear do not present anteromedian flexus. Anteroloph present and separate from anterocone in young, but anteroloph joining with anterocone in specimens with more advanced wear; posteroloph small joined to metacone in specimens with more advanced wear. Paracone of M1 with small crest that joins the mesoloph, creating an internal fosseta. M2 with mesoloph, with or without a protoflexus. The third upper molar (M3) is reduced, and has a single posterior cup, which we equate to the hypocone; hypoflexus is diminutive. The anteroconid of the first lower molar (m1) is without an anteromedian flexid; the mesolophid is distinct on unworn m1 and m2; m2 and m3 with anterolabial cingulum.

KARYOTYPE: This species is characterized by 2 n = 62 and FNa = 64. This karyotype has been formerly associated with other epithets besides O. fornesi , such as O. eliurus (Wagner, 1845) and O. flavescens ( Myers and Carleton 1981; Svartman 1989; Andrades-Miranda et al., 2001; Pereira and Geise, 2009; Di-Nizo et al., 2015).

HABITAT: Oligoryzomys mattogrossae is an inhabitant of open vegetation biomes such as the Cerrado and Caatinga, but can also be found in formations in the transition with Amazonian forest. No information about the vegetation of the type locality was provided in the description of O. mattogrossae (Allen, 1916) , but the vegetation along the Papagaio River, including the Utiariti region, is gallery forest.

COMPARISONS: Oligoryzomys mattogrossae differs from all other Oligoryzomys species by its unique karyotype. In addition, O. mattogrossae differs from other Oligoryzomys that occur in Brazil by a combination of other characters including (1) yellowish ventral pelage and (2) dorsal coloration without a defined limit with ventral pelage color, in comparison to a whitish venter with defined limit between lateral and ventral coloration in adult specimens of O. nigripes , O. microtis , O. utiaritensis , and O. stramineus (see table 1); (3) slightly bicolored tail, contrary to unicolored tail in O. nigripes and O. rupestris (other species of the genus also have slightly bicolored tails); (4) small size species (adult HBL <96 mm in average) as in O. rupestris , O. microtis , O. moojeni , O. flavescens , O. delicatus , O. messorius , O. fornesi , opposed to large size species (adult HBL> 100 mm in average) as O. nigripes , O. stramineus , and O. chacoensis . See table 1 for other comparisons.

Despite sharing the same type locality, O. mattogrossae differs from O. utiaritensis by its karyotype with 2 n = 62 and FNa = 64 ( O. utiaritensis 2 n = 70 and FNa = 74), and a combination of morphological characters including (1) yellowish ventral pelage, contrary whitish ventral coloration in O. utiaritensis , (2) dorsal coloration without a defined limit with ventral pelage color, in comparison to a whitish venter with defined limit between lateral and ventral coloration in adult specimens of O. utiaritensis (fig. 2). O. mattogrossae and O. utiaritensis are also readily distinguished by size, as O. utiaritensis is a larger species (see Agrellos et al., 2012, for measurements of other Oligoryzomys species ).

ETYMOLOGY: Oligoryzomys mattogrossae was named by J.A. Allen based on its type locality in Mato Grosso state .

SPECIMENS EXAMINED: See appendix 1.

REMARKS: Oligoryzomys mattogrossae was described by Allen (1916) based on two specimens, the holotype from Utiariti, and one paratype from “Guatsué”; the latter locality was not located, but Paynter and Traylor (1991) suggest that it is presumably on middle Rio Papagaio in Mato Grosso state .

Figures

FIGURE 2. Ventral views of the skin of the type specimens of Oligoryzomys. A, From left to right, Oligoryzomys mattogrossae (AMNH37542, holotype; HBL = 95 mm), O. microtis (AMNH37090, holotype; HBL = 93 mm), and O. utiaritensis (AMNH37541, holotype; HBL = 100 mm); B, O. fornesi (CEM3562, paratype; HBL = 82 mm).

FIGURE 3. Dorsal, ventral, and lateral views of the skull and mandible of a recently collected specimen of O. mattogrossae (CRB3141). Bar scale = 10 mm.