Scapteromys meridionalis, Quintela, Fernando Marques, Gonçalves, Gislene Lopes, Althoff, Sérgio Luiz, Sbalqueiro, Ives Jose, Oliveira, Luiz Flamarion Barbosa & Freitas, Thales Renato Ochotorena De, 2014

Quintela, Fernando Marques, Gonçalves, Gislene Lopes, Althoff, Sérgio Luiz, Sbalqueiro, Ives Jose, Oliveira, Luiz Flamarion Barbosa & Freitas, Thales Renato Ochotorena De, 2014, A new species of swamp rat of the genus Scapteromys Waterhouse, 1837 (Rodentia: Sigmodontinae) endemic to Araucaria angustifolia Forest in Southern Brazil, Zootaxa 3811 (2), pp. 207-225 : 213-221

Scapteromys meridionalis sp. n.

Plateau Swamp Rat

Figures 5–10 ; table 2

Holotype. Adult male, FURB 20253 (original number FQ 82), with skin, skull, post-cranial skeleton and fluidpreserved left forefoot and hindfoot, collected by F. M. Quintela on 16 October 2012. Frozen tissue samples (FQ 82) deposited in Department of Genetics at UFRGS; suspension of bone-marrow in Carnoy’s fixative (number FQ 82) was deposited in Department of Genetics at UFPR. Karyotype 2n=34, FNa=40.

Type locality. São Francisco de Paula municipality (29º29’73”S, 50º13’49”W; 913 m above sea level), Rio Grande do Sul State, Brazil.

Paratypes. Four topotypes ( FURB 20156, FURB 20252, FURB 20285 and FURB 20286) were collected between April 2012 and October 2012. Eighteen specimens collected between 2005 and 2012 in the following localities in southern Brazil: Santa Catarina State—Água Doce ( FURB 9972), Campo Alegre ( FURB 12658), Campo Belo do Sul ( FURB 15129, 15166), Doutor Pedrinho ( FURB 18676, 18993, 18996, 18999, 20044), Passos Maia ( FURB 18908), São Domingos ( FURB 12309); Paraná State—São Mateus do Sul ( FURB 15364), Candói ( FURB 15979), São José dos Pinhais ( UFPR 985, 1036, 1052, 1059, 1063) ( Fig.1 ). Skins, skulls ( FURB 9266 and FURB 15364 with missing skulls), fluid-preserved carcass and frozen tissue samples are housed at FURB.

Distribution. Known from shrub and herbaceous palustrine systems in the biogeographic domains of Paraná and Araucaria angustifolia Forest , from southern Paraná to Northern Rio Grande do Sul states (a highland region called “ Serra Geral”), in altitudes between 530 and 1017 m.

Diagnosis. A small-sized, darker furred Scapteromys species; 2n = 34/36; tail bicolored mainly in the proximal half; quadrate mesopterygoid fossa; median palatine process present; hamular processes of pterygoid with straight borders; thenar of manus laterally extended.

Description. Pelage dense and soft, tawny gray in dorsum ( Fig. 5 ), darker on the top of the head and on the middle and posterior central regions, but without forming a clear banding pattern; guard-hairs about 14 mm over the back, all eumelanic; overhair about 10 mm over the back, dichromatic, with a distal feomelanic band and most of its length eumelanic, including the distal tip; underhair about 7 mm over the back, with the same banding pattern of the overhair. Ventral pelage ( Fig. 5 ) whitish gray, without clear limit with darker flank parts, except by the middle abdomen. Ventral pelage is composed by over- and underhair; overhairs about 10 mm in middle chest, eumelanic in the basis and the mid region and feomelanic in the distal region; underhair about 5.5 mm in middle chest with the same banding pattern of overhairs. Presence of superciliary, mystacial, genal and inconspicuous submental vibrissae; measurements of largest vibrissae from holotype: mystacial—31.8 mm, superciliary—23.4 mm, genal—26.30 mm, submental—10.04 mm; longest mystacial not reaching the bases of pinnae when laid back alongside head. Rounded ears, densely covered by 3 mm long thick hairs, eumelanic in most of its length and feomelanic in the distal tip. Tail about 92% of the head-body length; densely hair covered; bicolored in the proximal half, with the dorsal region dark brown and the ventral region tawny, dark brown in the distal half; tail uniform dark in some paratypes; 6–10 mm terminal pencil; hair arranged in triads in each scale, with the central slightly longer than the laterals; eumelanic hair predominate in dorsal and ventral distal half while eumelanic hair cover the ventral proximal half; hairs in ventral proximal half (about 7 mm) are longer than in other regions (about 3 mm), forming a kind o fringe. Mammae eight in pectoral, axial, abdominal and inguinal pairs.

Hind foot about 25% of head-body length; digits II, III and IV subequal in size; undeveloped interdigital webs, reaching about 18% of the height between digits II and III and 34% of the height between digits III and IV; densely covered by hair (eumelanic in proximal half and feomelanic in distal half) in metapodial and digits; most distal hair reaching until about the first third of claws; grooved claws; thenar pad about twice the size of the largest digital pad, laterally extended ( Fig. 6 ); interdigital pads 2 and 3 subequal in size, followed by interdigital 4, interdigital 1 and hypothenar in descending order of size. Forefoot densely covered by feomelanic hair in metapodial and digits, not covering the claws; digits II, III and IV subequal in size; well-developed claws, reaching about 68% of the length of digits I–IV; well-developed claw in vestigial pollex, surpassing its extremity; five pads in plantar forefoot, thenar, hypothenar, and interdigitals 2, 3 and 4; interdigital pads subequal in size; hypothenar about 1.5 x thenar size and 4 x interdigital pad size.

Skull ( Fig. 7 A) characterized by elongate rostrum; gnathic process varying in size; well-developed anterior process of premaxillary but not forming a rostral tube (trumpet) with nasal extremity; slightly inflated incisive capsular projection; nasofrontal suture V shaped; deep zygomatic notches; diagonally shaped lacrimal; horizontally elongated nasolacrimal foramen; broad zygomatic plate, leaning forward, with an anterior rounded projection; elongate incisive foramina with their broadest point posterior to the transversal midline, posterior extremity reaching from anterolingual conule to hypoflexus; narrow antorbital bridge; well-developed tubercle in the anterior basis of zygomatic plate; median palatine process present; elongated anterior palatine foramen, followed by three punctual foramina in posterior palatine; hourglass-shaped interorbital region, with rounded margins and welldeveloped parietal dorsal anterolateral process; small frontal foramen; sphenopalatine foramen reduced and horizontally elongated; punctual ethmoid foramen localized in frontal, behind maxillary-frontal suture; optic foramen similar in size to M2; narrow zygomatic arch, anterior and posteriorly convergent and not surpassing the border of braincase in dorsal view; frontal-parietal-squamosal suture in the exact point of parietal anterior process extremity or little behind this process; presence of a tubercle in squamosal border, anteriorly to squamosal root of zygomatic; visible and elongated jugal; mesopterygoid fossae narrow, slightly divergent, extending anteriorly behind or between posterior M3 alveoli; sphenopalatine vacuities divided by a narrow strut; parapterygoid fossae shallow and subequal in size with quadrate mesopterygoid fossae; hamular processes of pterygoid straight shaped and slightly divergent; alisphenoid strut present, separating buccinator-masticatory foramen and foramen ovale accessorius; large and broad petrotympanic fissure, with stapedial spine varying in size; carotid circulatory pattern 1 of Voss (1988); small carotid canal and stapedial foramen; moderately inflated tympanic bulla with size similar to superior molar row; thin malleus; orbicular apophisis present; hamular process of squamosal with straight borders ( Fig. 8 ); postglenoid foramen larger or subequal in size with subsquamosal foramen; braincase not inflated in adults; basioccipital with undeveloped median crest; inflated occipital condyle, surpassing the braincase borders in ventral view; paroccipital process well-developed; interparietal varying in length and width; inflated mastoid with a large posterior foramen in posterior border; exoccipital inflated with conspicuous longitudinal and transversal crests.

Mandible ( Fig. 7 A) short and delicate, with height about 45% of length without incisors; elongate and narrow ramus; anterior extremity of diastema located slightly above molar plane; conspicuous mental foramen, visible from lateral and occlusal views and subdivided in an anterior shorter and a posterior larger foramen; undeveloped masseteric ridges; superior masseteric ridge forming an undeveloped tubercle under m1; undeveloped capsular projection under coronoid ramus; delicate coronoid process isolated from condyloid by a shallow but strongly concave sigmoid notch; coronoid process broad, isolated from a less broad angular process by a shallow mandibular notch.

Upper incisors orthodont and orange; lower incisors grooved and much paler. Upper molars ( Fig. 9 ) parallel, crested, with labial cusps higher than lingual cusps. Main cusps alternate. M1 with well-developed anteromedian flexus in specimens with little-worn molars, clearly dividing the procingulum in anterolingual and anterolabial conules, which are subequal in size; well-developed anteroloph, parallel to anterolabial conule and surpassing its outer border; anteroloph proximally isolated from anterolabial conule by anteroflexus in specimens with few-worn molars; anteroloph coalescent with anterolabial conule, surpassing the anterolabial outer border in specimens with well-worn molars; paraflexus and metaflexus substantially longer than protoflexus and hypoflexus and curved backward in its proximal half; protoflexus and hypoflexus straight; protocone and hypocone subequal in size and larger than paracone and metacone; paracone and metacone subequal in size; well-developed mesoloph, distally separated from paracone by a shallow mesoflexus and surpassing the paracone outer border; posteroloph conspicuous only in specimens with unworn molars; posteroloph fused with metacone in specimens with moderate or advanced molar wear. M2 lacking conules; well developed anteroloph isolated from paraflexus by deep and backward-curved anteroflexus; paracone subequal in size with metacone; Mesoloph separated from paracone by a shallow mesoflexus and not surpassing the paracone outer border; paraflexus and metaflexus deep and curved backward; hypocone visually larger than protocone; posteroloph conspicuous in specimens with unworn molars and fused with metacone in specimens with worn molars; M3 with anteroloph separated from metacone by a shallow anteroflexus in specimens with few-worn molars; paracone well-developed connected to mesoloph by the paralophule; mesoloph connected to paracone; protocone larger than hypocone; shallow hypoflexus; posteroloph absent; in worn molars the only evident cusps are paracone, metacone and protocone. Lower molars ( Fig. 9 ) parallel and crested, with lingual cusps higher than labial ones; main cusps alternate; m1 with shallow anteromedian flexid only in specimens with unworn molars; metaconid and entoconid subequal in size; hypoconid slightly larger than protoconid; well-developed protostylid, separated from protoconid by a shallow protoflexid; hypoflexid comparatively shallow and straight; metaflexid deep and strongly frontward in its proximal half; welldeveloped mesolophid, separated from metaconid by a shallow entoflexid; posteroflexid deep and slightly frontward; well-developed posterolophid; m2 lacking conulids; metaconid slightly larger than entoconid; protoconid and hypoconid subequal in size; undeveloped protostylid, separated from protoconid by a shallow protoflexid; hypoflexid relatively shallow and straight; mesoflexid deep and frontward; well-developed mesolophid separated from entoconid by a shallow entoflexid; posteroflexid deep and straight; well-developed posterolophid; m3 lacking conulids; protostylid distinguishable only in specimens with unworn molars; metaconid larger than entoconid; protoconid larger than hypoconid; mesolophid fused with entoconid; mesoflexid deep and frontward; hypoflexid deep and straight; well developed posterolophid, distally connected to entoconid and characterizing the posteroflexid as a fossette.

Axial skeleton composed by thirteen ribs, 19 thoracicolumbar vertebrae, 5 sacral vertebrae, 30 caudal vertebrae; presence of a conspicuous neural spine in the second thoracic vertebrae. Scapula thin and translucent, except by borders; acromion with conspicuous concavity; deep notch, reaching about a quarter of the spine length. Humerus robust; well-developed head; lesser tubercle more prominent than greater tubercle; less-developed lateral epicondylar crest; well-developed deltopectoral crest, with slight concavity in inferior border; supratrochlear foramen present. Ulna fused to radius except by a small segment behind trochlear notch, forming a small and elongated fissure. Elongated ilium and gluteal fossa; conspicuous femoralis tuberosity; narrow pelvic symphysis. Elongated tibia, with well developed lateral and medial crests. Fibula thin, attached to tibia behind the distal half.

Stomach bilocular-discoglandular ( Carleton 1973); shallow incisura angularis, surpassing slightly the esophageal opening and giving a bipartite pattern softly marked.

Comparisons. Scapteromys meridionalis differs from S. aquaticus by: (1) diploid number of 34 or 36 chromosomes (versus 2n= 32 in aquaticus ); (2) smaller size, including head-body length, tail length, and 15 craniodental measurements ( Table 2 ); darker and grayer dorsal pelage (versus more tawny in S. aquaticus ) ( Fig. 5 ). Scapteromys meridionalis differs from S. tumidus by: (1) diploid number of 34 or 36 chromosomes (versus 2n= 24 in S. tumidus ); (2) smaller size (on average), including all external measurements, weight and craniodental measurements except length of tympanic bulla and breadth of occipital condyles ( Table 2 ); (3) darker and grayer dorsal pelage (versus more tawny in S. tumidus ) ( Fig. 5 ); (4) laterally extended thenar pad of manus, reaching almost the height of superior proximal border of pollex nail in lateral view (versus ventral thenar pad of manus in S. tumidus ) ( Fig. 6 ). This distinction was evident only in fluid preserved forefeet, which included the holotype and one paratype of Scapteromys meridionalis and 39 specimens of S. tumidus in our analysis; (5) parallel edges of hamular process of pterygoid (versus edges with inner concavity in S. tumidus ) ( Fig 8 ). This is a consistent cranial character; parallel edges were present in all Scapteromys meridionalis and a single S. tumidus specimen while 119 specimens of S. tumidus showed edges with inner concavity. Auxiliary character: proximal dark median ventral stripe was absent in the tail of specimens with a bicolored tail. Forty-nine of 55 examined specimens of S. tumidus with a bicolored tail showed a proximal dark median ventral stripe, while the other 12 specimens had a uniform dark tail; S. aquaticus showed less conspicuous bicolored pattern, but the median ventral stripe was evident in all adults. Observation: young specimens of S. aquaticus and tumidus are darker and grayer than subadults and adults, resembling the color pattern of S. meridionalis . However, all subadults and adults of S. tumidus specimens examined had a conspicuous tawny-gray pattern, clearly distinguishable from S. meridionalis . Some adult specimens of S. aquaticus were grayer than S. tumidus but conspicuously tawnier than the taxon described.

included) and S. tumidus topotypes [AMNH 206243-20658; n varying from 12 to 16], *p <0.05, **p <0.01, ***p <0.001, ns = not significant.

Karyotype. Individuals of the new species had a diploid number (2n) of 34/36 chromosomes and an autosomal fundamental number (FNa) of 40 arms. The holotype showed 2n=34 and FNa=40. See above for karyotype description.

Etymology. Reference to Meridional Plateau, the geological formation where the specimens of the type series were collected.

Natural history. Specimens of S. meridionalis were collected in palustrine open areas (swamps and flooded grasslands) of the Meridional Plateau, Atlantic Forest domain, mainly in soggy soils with predominance of Eryngium pandanifolium (Apiaceae) and Baccharis sp. ( Asteraceae ) ( Fig.10 ). The species was found sympatric with the didelphid Monodelphis dimidiata Wagner and the sigmodontines Akodon montensis Thomas , Holochilus brasiliensis Desmarest , Oligoryzomys flavescens Waterhouse , Oxymycterus nasutus Waterhouse and an undescribed form of Deltamys . Despite its distribution across the Atlantic Forest domain, this new species seems to be an inhabitant of open palustrine systems, which is characteristic of this genus.

Figures

FIGURE 1. Distributional range of the three Scapteromys species (Green, Scapteromys sp. n.; light gray, S. aquaticus; dark gray, S. tumidus) and collecting sites of Scapteromys sp. n. (Brazil: 1 — Rio Grande do Sul: São Francisco de Paula, 2 — Santa Catarina: Campo Belo do Sul, 3 — Santa Catarina: Água Doce, 4 — Santa Catarina: Doutor Pedrinho, 5 — Santa Catarina: Campo Alegre, 6 — Santa Catarina: São Domingos, 7 — Santa Catarina: Passos Maia, 8 — Paraná: São José dos Pinhais, 9 — Paraná: São Mateus do Sul, 10 — Paraná: Candói). Red solid triangles represent localities with presence of 2 n = 34, and blue solid triangles indicate the presence of 2 n = 36. The circled triangle indicates the type locality.

FIGURE 5. Dorsal (upper), ventral (middle) and bottom (bottom) views of skins of (A) Scapteromys meridionalis (holotype, FURB 20253), (B) S. aquaticus (FCM 500) and (C) S. tumidus (FURB 20290). Bar = 10 mm.

FIGURE 6. Thenar pad of manus (indicated by the red arrow) and its respective morphology in Scapteromys meridionalis (holotype, FURB 20253) (right) and S. tumidus (FURB 20290) (left). Bar = 1 mm.

FIGURE 7. (A) Dorsal (left), ventral (middle) and lateral (right) views of skull and labial view of mandible (bottom right) of (A) Scapteromys meridionalis holotype (FURB 20253). (B) S. aquaticus (FCM 489) and (C) S. tumidus (FURB 20289). Bar = 5 mm.

FIGURE 8. Hamular process of pterygoid (red square) and its respective shapes in Scapteromys meridionalis (holotype, FURB 20253) (left) and S. tumidus (MCNU 3378) (right). Bar = 1 mm.

FIGURE 9. Occlusal views of upper and lower molar series of Scapteromys meridionalis holotype (FURB 20253). Bar = 1 mm.

FIGURE 10. Biogeographic regions and provinces in South America (A), with details of the study area (in dark blue) and sampling sites of Scapteromys meridionalis [For details see Material and Methods] (B); and Araucaria angustifolia Forest habitat (C). Sources: A, adapted from Morrone (2006); C, Photography of Araucaria angustifolia Forest: G. L. Gonçalves.

Tables

TABLE 2. External and cranial measurements (in millimeters) of Scapteromys meridionalis, Scapteromys aquaticus and Scapteromys tumidus (mean [X] ± one standard deviation [SD], the observed range [in parenthesis], and the sample size [n]). P indicates significance levels of differences obtained by t - test (Scapteromys meridionalis S. aquaticus / Scapteromys meridionalis x S. tumidus; matrices composed by all Scapteromys. sp. n., S. aquaticus listed in Appendix (n varying from 9 to 42; weight

Scapteromys meridionalis		Scapteromys aquaticus		Scapteromys tumidus		P
X ± SD Range	N	X ± SD Range	n	X ± SD Range	n
HBL 135 ± 13 (114–135)	15	159 ± 12 (111–188)	42	159 ± 14 (126–208)	101	***/***
LT 114 ± 9 (101–125)	15	136 ± 16 (94–165)	42	140 ± 10 (110–161)	94	***/***
Ear 22 ± 3 (13–26)	15	21 ± 2 (17–24)	41	23 ± 2 (17–29)	98	ns/**
HF 34 ± 2 (32–37)	15	35 ± 2 (32–39)	42	40 ± 2 (36–45)	101	ns/***
BI 2.57 ± 0.18 (2.28–3.21)	23	3.19 ± 0.38 (2.42–4.31)	16	3.33 ± 0.31 (2.27–4.29)	215	***/***
LMR 5.62 ± 0.21 (5.17–5.87)	23	6.48 ± 0.30 (6.13–7.02)	16	6.59 ± 0.28 (5.91–7.29)	209	***/***
LN 13.88 ± 0.81 (12.56–15.88)	23	14.62 ± 1.53 (12.29–18.56)	16	15.45 ± 1.11 (12.33–17.75)	215	ns/**
BR 5.67 ± 0.40 (5.18–7.12)	23	6.93 ± 1.19 (5.85–10.87)	16	6.74 ± 0.36 (5.33–7.88)	222	***/***
LTB 5.77 ± 0.37 (4.51–6.45)	23	5.90 ± 0.52 (5.36–6.92)	10	5.77 ± 0.31 (4.99–6.42)	195	ns/ns
BB 15.11 ± 0.37 (13.76–15.82)	23	15.64 ± 1.22 (12.19–17.13)	11	15.89 ± 0.54 (14.53–17.38)	200	*/***
BZB 3.27 ± 0.33 (2.64–3.86)	23	3.72 ± 0.37 (2.76–4.62)	16	3.77 ± 0.31 (2.82–4.75)	224	***/***
LIB 5.18 ± 0.21 (4.82–5.49)	23	5.76 ± 0.32 (5.26–6.44)	15	5.46 ± 0.23 (4.91–6.24)	224	***/***
LR 13.22 ± 0.91 (11.23–15.19)	23	13.17 ± 1.37 (10.93–15.64)	14	13.56 ± 1.11 (9.37–16.07)	213	ns/ns
DFM 6.89 ± 0.47 (5.56–7.73)	23	7.45 ± 0.62 (6.62–8.78)	15	7.63 ± 0.52 (6.42–8.76)	206	***/**
BFM 1.77 ± 0.22 (1.46–2.11)	23	1.89 ± 0.23 (1.56–2.24)	16	2.01 ± 0.22 (1.73–2.58)	215	**/***
CIL 33.26 ± 1.68 (29.62–36.27)	23	35.13 ± 3.11 (30.07- 40.01)	9	36.82 ± 2.09 (30.42–42.08)	199	*/***
TL 35.74 ± 1.56 (32.92–39.07)	23	38.09 ± 3.11 (32.89–43.43)	9	38.77 ± 2.03 (32.44–43.57)	197	**/**
PL 5.57 ± 0.42 (4.82–6.46)	23	6.52 ± 0.77 (5.5–8.01)	19	6.5 ± 0.5 (5.4–8.0)	219	***/***
LD 8.73 ± 0.71 (7.54–10.03)	23	8.83 ± 0.89 (7.11–10.46)	15	9.42 ± 0.79 (6.91–11.18)	219	ns/ns
OL 11.33 ± 0.37 (10.13- 12.02)	23	11.92 ± 0.77 (10.64–13.08)	10	12.47 ± 0.62 (10.44–14.59)	220	**/***
HB 12.29 ± 0.42 (11.12–12.970)	23	12.93 ± 0.44 (12.18–13.61)	10	13.08 ± 0.43 (11.89–14.12)	186	***/***
BZ 17.43 ± 0.48 (16.31–18.13)	22	18.71 ± 1.29 (16.72–21.42)	11	19.18 ± 0.93 (16.17–21.52)	204	***/***
LIF 7.44 ± 0.56 (5.81–8.53)	23	7.71 ± 0.69 (6.41–9.07)	15	8.18 ± 0.62 (6.02–9.93)	220	ns/**
BIF 2.63 ± 0.31 (2.02–3.13)	23	2.54 ± 0.24 (2.18–2.86)	15	2.25 ± 0.23 (1.65–2.84)	223	ns/***
BOC 8.01 ± 0.33 (7.54–8.43)	22	8.86 ± 0.32 (8.48–9.62)	9	8.91 ± 0.33 (8.02–9.73)	200	***/***
Weight 77 ± 12 (50–91)	15	211	1	118 ± 28 (50–165)	61	***