Unveiling hidden diversity of Oecomys (Rodentia: Cricetidae) from Brazilian Central Amazonia: description of a new species and new lineages

The arboreal rice rat of the genus Oecomys Thomas, 1906 is one of the most speciose genera of the subfamily Sigmodontinae, with 19 species currently recognized and occurring from eastern Panama to northern Argentina, Paraguay, and in northern, central and eastern Brazil. Herein we describe a new species using an integrative approach based on molecular, morphological, and morphometric data. We used in our assessment recently collected specimens from the states of Pará and Rondônia, one of the most deforested regions in Brazil. We examined 51 specimens of Oecomys from museum collections including name-bearing types from most of the distributional range of the genus. We also sequenced 32 specimens of Oecomys, and for the molecular analyses, we used the mitochondrial marker Cytochrome b and the nuclear marker intron 7 of β-fibrinogen. Our mitochondrial marker results recovered a strongly supported clade composed of two divergent clades (3.78%), one including lineages of O. bicolor and O. cleberi, and the other clade representing the new species. The topology of concatenated mitochondrial and nuclear data also recovered Oecomys sp. nov. as a sister lineage of the O. bicolor and O. cleberi clade. Also, both markers recovered new lineages from the O. bicolor and O. cleberi species group. The new species can be discriminated from other Oecomys species by pelage colour and craniodental characters, such as absent or small mastoid fenestra, and the presence of alisphenoid strut, small subsquamosal fenestra, presence of sphenopalatine vacuities, and presence of accessory loph of M1 and M2 paracones. The new species occurs exclusively in the Rondônia centre of endemism, delimited by the rivers Amazon to the north, Tapajós to the east, and Madeira to the west. The description of this new Oecomys increases the diversity, and also contributes to elevate Amazonian Sigmodontinae species richness and endemism in this still poorly known biome. http://zoobank.org/urn:lsid:zoobank.org:7477D37A-4D02-443F-B0FB-149379BEDE92


Introduction
The genus Oecomys Thomas, 1906 currently comprises 19 valid species (Pardiñas et al. 2016(Pardiñas et al. , 2017;;Rocha et al., 2018;Saldanha & Rossi, 2021) of small to medium-sized arboreal rodents (head and body: 90-150 mm), that occur from eastern Panama in Central America to northern Argentina, Paraguay, and northern, central and eastern Brazil in South America, with the highest diversity of species found in the Amazon basin (Carleton & Musser, 2015;Pardiñas et al., 2017).Recent studies point to the existence of species complexes in the genus (Rosa et al., 2012;Pardiñas et al., 2016;Su arez-Villota et al., 2018;Saldanha & Rossi, 2021), as attested by several species which have been recently described or revalidated (Carleton et al., 2009;Pardiñas et al., 2016;Rocha et al., 2018;Saldanha & Rossi, 2021).The most taxonomically complete study on the systematics of Oecomys included 14 of the 17 species recognized at the time, and suggested the existence of 10 species and five species complexes, among which the complex O. bicolor/O.cleberi comprises eight distinct lineages (Su arez-Villota et al., 2018).
Until recently, O. cleberi Locks, 1981 was recognized as restricted to the Brazilian Cerrado, but the species has been recorded in the southern portion of the Amazonia (Su arez-Villota et al., 2018;Saldanha et al., 2019) and in seasonal forests marginal to the Atlantic Forest (Brandão et al., 2022).Differently, O. bicolor Tomes, 1860 has a wider distribution that extends from the trans-Andean tropical forest plains in eastern Panama and western Ecuador to the east of Bolivia and central Brazil, reaching as far as eastern Amazonia (Carleton & Musser, 2015).
Due to great morphological similarity, O. cleberi has long been associated with O. bicolor (Carleton & Musser, 2015).Musser & Carleton (2005) associated O. cleberi with O. bicolor and O. paricola, though the latter stands apart from the first two by exhibiting a distinct reddish or tawny brown dorsal colour and creamier grey-based ventral colour, whereas O. bicolor and O. cleberi have self-coloured white ventral colour and orangish brown dorsum (Rocha et al., 2012;Su arez-Villota et al., 2018).Rocha et al. (2012) recognized the validity of O. cleberi and its sister relationship with O. bicolor based on sequences of the mitochondrial gene Cytochrome b (Cytb).Similarly, Su arez-Villota et al. (2018) and Saldanha et al. (2019) recognized the close relationship between bicolor and cleberi based on mitochondrial and nuclear markers.The former authors recovered O. cleberi as a monophyletic group composed of two distinct lineages (central and northwestern clades), and O. bicolor as a polyphyletic group that includes six distinct lineages (central, eastern, northern, southern, western, and westernmost clades).Both species were grouped in the O. bicolor/O.cleberi species group by Su arez-Villota et al. (2018).Saldanha et al. (2019) Villota et al., 2018), geographically corresponding to samples from the north of the state of Mato Grosso and from central Brazil, respectively.
Specimens of Oecomys apparently associated with the O. bicolor and O. cleberi species group were collected by some of the authors during field expeditions in the Jamari National Forest, municipality of Itapuã do Oeste, state of Rondônia, Brazil.Direct comparisons of these recently collected specimens with congeners, including morphological and molecular analyses, confirmed that they belong to a hitherto undescribed species occurring in the Brazilian central Amazonia, which we formally describe herein.

Morphological and morphometric analyses
In the specimens examined morphologically, we observed the patterns of the pelage of the head, dorsum, venter, manus, and feet, as well as the colouration and arrangement of hairs on the tail.Cranially, we analysed the morphology of the orbital and supraorbital region, palate, basicranium, and auditory region, including the presence and position of foramina and sutures.The morphology of the molars were also examined.The nomenclature used in character descriptions follows Reig (1977), Voss (1991), Weksler (2006), andSaldanha &Rossi (2021).
For the morphometric analyses, specimens were grouped into five different age classes following Voss (1991).Only specimens considered as adults, i.e., with the third upper molar fully erupted (age classes 3-5), were included in the statistical analyses.Standard descriptive univariate statistics were calculated for all external and craniodental measurements.Principal Component Analyses (PCA) and Discriminant Function Analysis (DFA) were performed in order to assess whether morphometric data are congruent with our molecular results as well as with the qualitative morphological comparisons among the closely related taxa, and with previously published molecular data.In DFA, the specimens were identified a priori as O. bicolor, O. cleberi, and the new species herein described.For these analyses, craniodental measurements were log-transformed, and for PCA the principal components were extracted from the variance-covariance matrix.For DFA, the canonical variates were extracted from the variance-covariance matrix.Statistical analyses were performed using SPSS v. 22.0 for Windows with a significance level of 5%.

Phylogenetic analyses
The genomic DNA was obtained from ethanol-preserved tissues of seven Oecomys specimens recently collected from the Jamari National Forest -Rondônia, one specimen from Juruti -Par a, and 24 specimens of the O. bicolor/O.cleberi species group.The extraction was performed using the saline protocol (Aljanabi & Martinez, 1997), with modifications.For molecular analyses, we used the mitochondrial Cytochrome b gene (Cytb) with MVZ05 and MVZ16 primers (Smith & Patton, 1993), and the intron 7 of b-fibrinogen nuclear gene (i7-Fgb) with bI7-mammL and bfib-mammU primers (Matocq et al., 2007).The amplification and sequencing were carried out following Saldanha et al. (2019).These sequences were aligned to assemble the consensus in the software Geneious v. 7.1.3(Biomatters, available at http://www.geneious.com;Kearse et al., 2012), and deposited in GenBank under the accession numbers OR339662-OR339700 (Supplemental Table S1).In addition, sequences of 101 specimens of the O. bicolor/O.cleberi species group and 41 sequences of other species of Oecomys were also downloaded from GenBank.Subsequently, the sequences were edited and aligned by the ClustalW tool in BioEdit 7.0.5.3 (Hall, 1999).
Phylogenetic relationships based on Cytb only and concatenated data matrices were analysed separately, using a Bayesian approach (BI) in MrBayes 3.2.6 (Ronquist et al., 2012) with two runs, four chains, 30 million generations, sampled every 1000 generations with 25% of burnin.The trees were estimated with 50% majority rule consensus and generate Bayesian Posterior Probabilities (pp).We also used a Maximum likelihood (ML) approach in Garli 2.0 (Zwickl, 2006) with bootstrap of 1000 replicates.The analyses were conducted at online platform CIPRES (Miller et al., 2010).The trees of bootstrap were summarized with 50% majority rule consensus on SumTrees (Sukumaran & Holder, 2010).The genetic distances within and among the clades were calculated in MEGA7 (Kumar et al., 2016) by uncorrected p-distance method.

Results
According to Carleton & Musser (2015), 10 nominal taxa are currently recognized as synonym of O. bicolor and among them is O. milleri Allen, 1916, which deserves special attention as the species was described based on specimens from Barão de Melgac ¸o, state of Rondônia, Brazil, approximately 400 km from our specimens from Jamari National Forest.As the skull of the holotype of O. milleri (AMNH 37117) is damaged, we were not able to include it in morphometric analyses.However, a detailed morphological examination of the holotype's skin (Supplemental Fig. S1) by one of the authors, along with the craniodental dimensions provided in the original description, led us to consider that O. milleri cannot be assigned to the new species analysed in the present study, as discussed below.In this sense, the specimens recently collected represent an undescribed species of Oecomys with no name available in the literature, which we formally describe herein.Relevant summaries of morphometric variation and qualitative traits are provided in Tables 1 and 2 Type locality.Jamari National Forest, municipality of Itapuã do Oeste, state of Rondônia, Brazil (coordinates 09 10'48"S, 62 57'11"W; Fig. 4).
Geographic distribution.The species is known from three localities in the Brazilian states of Par a and Rondônia.In Par a state, it occurs in the municipalities of Juruti and Jacareacanga, south of the Amazon River and west of the Tapaj os River.In Rondônia, it has been recorded in the municipality of Itapuã do Oeste, east of the Madeira River.Based on these records, the species seems to be restricted to the area between the Madeira and Tapaj os rivers in Brazil and to occur in sympatry with the northwestern clade of O. cleberi (Fig. 4).
Etymology.The specific epithet jamari is to be treated as a noun in apposition.The species name refers to the type locality in the Jamari National Forest, which is a federal protected area pioneer in activities of sustainable use in Brazil and one of the last remaining preservation areas in the state of Rondônia, which is under constant threat due to human activities (Dall'Igna & Maniesi, 2022).
Diagnosis.Oecomys jamari sp.nov. is a small species of Oecomys (mean HBL ¼ 96.95 mm, Table 1) that differs from congeneric taxa by the following combination of craniodental traits: Soft and dull orangish brown dorsal fur, composed of short grey-based hairs (5-8 mm); dirty white ventral fur composed of very light greybased hairs, except for the throat, which is self-white; thin but conspicuous lateral band of grey-based hairs; caudal tuft present (about 5 mm, Fig. 2).Small skull (ONL ¼ 26.66-27.9mm, n ¼ 2); U-shaped posterior edge of the nasals, aligned with or surpassing the maxillary-frontal suture; mastoid fully ossified or with a  Allen (1916).See "Materials and Methods" section for abbreviations.The measurements are presented as follows: mean ± standard deviation/minmax (sample size).small fenestra that does not contact the exoccipital; subsquamosal fenestra, alisphenoid strut, and sphenopalatine vacuities present; accessory loph in the paracone of the first and second upper molars present; primitive pattern of carotid circulation (pattern 1 sensu Voss 1988, Fig. 3).
Morphological description.Dark brown rostrum with orange tones in orbital region.Abundant mystacial vibrissae extending beyond the distal edge of the ears when folded close to the body.Ears with short dark brown hairs on external face.Dorsal pelage soft and short, with dark grey-based and reddish brown-tipped hairs ranging from 5-8 mm; dark brown-tipped hairs also present on the midline of the dorsum.Lateral pelage of the body lighter than the dorsal pelage.Ventral pelage composed of very light grey-based hairs, giving a dirty white appearance on chest and abdomen, sometimes also on inguinal region; self-white hairs restricted to the throat, sometimes also present on the inguinal region; narrow but conspicuous lateral band of greybased hairs, extending from the forelimbs to the hind limbs (Fig. 2).Four pairs of mammae, arranged as follows: inguinal, abdominal, postaxial, and pectoral (Voss & Carleton, 1993).Manus short and dorsally covered with grey hairs on metatarsals and white hairs on tarsus.
Hind foot broad and usually covered with both white and black hairs, with grizzled appearance.Both manus and pes with claws moderate in length (1-2 mm) and with pads as for the genus: manus with two carpal and three plantar pads; hindfeet with a light brown patch on the metatarsals upper surface, central digits (II, III, and IV) longer than the outer digits (I and V), digit V semiopposable, six large plantar pads (fleshy and with interdigitals 1-4 set close together) with smooth skin between.Dark brown tail, unicoloured from basis to tip, with scales in a circular arrangement; three hairs associated with each caudal scale, the central one thicker and longer, exceeding two scales in length; small dark brown caudal tuft present, about 5 mm in length.Skull delicate, rostrum slightly longer and narrow, with a relatively long nasal (Table 2; Figs 3, 5).Anterior margins of nasal bones rounded and posterior margin U-shaped, with posterior end aligned or   S1.
Mandible with capsular process of lower incisor moderately developed, as a slight rounded elevation (Fig. 3).Masseteric ridges convergent anteriorly, and fused in the anterior portion below m1.Mental foramen laterally placed, and ahead of the confluence between the upper and lower ridges of the masseteric crests.Condyloid process robust, ending posteriorly to the angular process, which is very short; coronoid process short and posterodorsally oriented, below the level of the upper margin of the condyloid process.Sigmoid and angular notches shallow.
Comparisons.On average, Oecomys jamari sp.nov. is larger than O. bicolor and O. cleberi in several external and craniodental measurements (Table 1, Fig. 5).Externally, Oecomys jamari sp.nov.differs from the other two species by the dark reddish brown dorsal pelage versus fair reddish brown to orangish brown pelage; ventral fur made up of very light grey-based hairs, giving an appearance of dirty white in the region of chest and abdomen, occasionally extending until the inguinal region, versus completely white or cream; narrow but conspicuous lateral band of grey-based hairs, versus grey-based lateral band absent in O. bicolor and usually absent in O. cleberi.
Craniodentally, Oecomys jamari sp.nov.differs from O. bicolor and O. cleberi by its larger and wider cranial vault; mastoid fully ossified or with a small fenestra that does not contact the exoccipital, versus a usually large fenestra in contact with the exoccipital; small subsquamosal fenestra, versus a large subsquamosal fenestra; alisphenoid strut present, versus absent in O. bicolor and usually absent in O. cleberi (present in UFMT1372 and MSF2130); small sphenopalatine vacuities present, versus usually ossified in O. cleberi and variable in O. bicolor; accessory loph in the paracone of M1 and M2 present, versus absent in O. bicolor and usually absent in O. cleberi (present in UFMT1363, UFMT1372, MSF2341; Fig. 6).Oecomys jamari sp.nov.can also be discriminated from O. cleberi by exhibiting posterior margins of the nasals aligned or surpassing the maxillary-frontal suture, versus aligned but not surpassing the maxillary-frontal suture in the latter species (Table 2).
Considering that Oecomys jamari sp.nov. is possibly restricted to the Madeira-Tapaj os interfluve, a region that encompasses the type locality of O. milleri Allen, 1916 from Barão de Melgac ¸o, state of Rondônia (Fig. 4), comparisons between these two forms deserve attention.The skin of the holotype of O. milleri (AMNH37117) is dirty in the venter, appearing to be greyish.However, a closer look allows one to see self-white fur in part of the abdomen and chin (Supplemental Fig. S1).Therefore, the holotype of O. milleri differs from Oecomys jamari sp.nov.by exhibiting self-white venter, with no conspicuous lateral bands of grey-based hairs, versus a dirty white venter composed of very light grey-based hairs on chest and abdomen, sometimes also on inguinal region (never on the throat), and conspicuous narrow lateral bands of greybased hairs.Cranially, the holotype of O. milleri exhibits posterior edge of the nasals aligned with the maxillaryfrontal suture, versus aligned with or surpassing the  Villota et al., 2018;Saldanha et al., 2019).Therefore, we considered the O. bicolor and O. cleberi species group to calculate Cytochrome b genetic distances.Values above diagonal correspond to standard deviation and bold numbers refer to genetic distance within clades.Values in percentage.maxillary-frontal suture in Oecomys jamari sp.nov.; and a large fenestra on the mastoid, versus a small or absent fenestra on the mastoid in Oecomys jamari sp.nov.The M1 accessory loph in the paracone of the first and second upper molars is present in Oecomys jamari sp.nov.and absent in O. milleri (Fig. 7).Additionally, several craniodental dimensions of the holotype of O. milleri provided by Allen (1916) in the original description do not overlap with those exhibited by Oecomys jamari sp.nov.In fact, the occipitonasal length (ONL), the length of upper diastema (LD), the greatest zygomatic breadth (ZB), and the coronal length of upper molars (CLM) are smaller in the holotype of O. milleri, while the breadth across the incisive foramina (BIF) and the length of incisive foramen (LIF) are larger when compared with Oecomys jamari sp.nov.(Table 1).S1.
Natural history.At the type locality (Jamari National Forest), seven specimens were captured in submontane open ombrophilous forest, with palm trees and vines (Supplemental Fig. S2).Two refers to males (one juvenile and one adult), four are lactating females collected in December, and one is a female with offspring collected in October.Captures took place in different strata, either through pitfall-traps, Sherman or cage traps, both installed on the ground and the understorey (approximately 1.5 metres high) and baited with pieces of pineapple soaked in cotton with cod liver oil.With a collection effort of 27,564 trap-nights, the capture success of these species for the area was 0.02%.Other small non-volant mammal species captured in the same sites of Oecomys jamari sp.nov.are the didelphid marsupials Didelphis marsupialis, D. albiventris, Marmosa sp., M. constantiae, Marmosops sp., Marmosops noctivagus, Metachirus myosuros, Monodelphis emiliae, M. glirina, M. saci, the cricetid rodents O. cleberi, Rhipidomys sp., the echimyid rodents Proechimys sp., Mesomys cf.hispidus, and the exotic murid rodent Rattus rattus.

Phylogenetic analyses
The phylogenetic analyses of Bayesian Inference (BI) and Maximum Likelihood (ML) with 174 Cytb sequences of Oecomys (matrix size ¼ 801 bp) recovered all lineages of the O. bicolor/O.cleberi species group (sensu Su arez-Villota et al., 2018) in a single clade (posterior probability [pp] ¼ 1; bootstrap ¼ 60%; Fig. 8).Most lineages could be associated with those recognized by Su arez-Villota et al. ( 2018), whose names are adopted here.However, three new lineages were recovered within the species group, two of which (herein named northern and north-central O. cleberi; Fig. 8) are nested in a monophyletic group with high support (pp ¼ 0.99) that also includes the two O. cleberi lineages (pp ¼ 1; bootstrap 95%) and the northern lineage of O. bicolor.The third new lineage (herein named north-central O. bicolor; Fig. 8) appeared as sister to the southern O. bicolor lineage with high branch support (pp ¼ 0.99; bootstrap ¼ 73%).Among the clades recovered, the north-central, northwestern and central O. cleberi had very low branch support.Finally, we were not able to associate several specimens to any of the lineages in the species group.Two of these specimens (MPEG [40734][40735] are closely related to the north-central, southern and westernmost O. bicolor, and the remaining appeared in basal positions within the species group, with very low branch supports (Fig. 8).
Specimens of Oecomys jamari sp.nov.were recovered in a highly supported clade (pp ¼ 1; bootstrap ¼ 100%) as sister to the O. bicolor and O. cleberi species group, with high support in the BI (pp ¼ 0.96; bootstrap ¼ 49%, Fig. 8).The Oecomys jamari sp.nov.had 3.78% of genetic divergence in relation to the O. bicolor and O. cleberi species group, and from 5.58% up to 9.62% in relation to other congeners.Genetic distances were 0.91% within Oecomys jamari sp.nov.and 2.15% within the O. bicolor and O. cleberi species group (Table 3).
The topology of concatenated data (Cytb þ i7-Fgb; Fig. 9) with 70 Oecomys sequences (samples were included only when data were available for the two

Morphometric analysis
Based on our concatenated topology, we considered specimens of the lineages northern, north-central, northwestern, and central O. cleberi as O. cleberi lato sensu in the morphometric analyses.And for analytical purposes, we considered as O. bicolor lato sensu the lineages southern and north-central O. bicolor, plus the specimens MPEG 40734-40735, which forms a monophyletic clade in our Cytb topology.In the PCA for Oecomys jamari sp.nov.(n ¼ 4), O. bicolor lato sensu (n ¼ 24), and O. cleberi lato sensu (n ¼ 17), the first two principal components (PC1 and PC2) together accounted for 64.56% of total variation.Based on this analysis, the Oecomys jamari sp.nov.partially overlaps with O. bicolor lato sensu and O. cleberi lato sensu (Fig. 10; Table 4).Along the PC1 axis, Oecomys jamari sp.nov.overlaps only with the larger specimens of O. bicolor lato sensu and O. cleberi lato sensu, revealing a slightly larger size of the new species.With regard to the PC2, Oecomys jamari sp.nov.almost entirely separates from O. bicolor lato sensu, but not from O. cleberi lato sensu, revealing a more similar shape of the skull with the latter.Among the most important variables are the condyle-incisive length (CIL), the condylo-zygomatic length (CZL), and the greatest zygomatic breadth (ZB) for PC1, all related to skull size, and the breadth of palatal bridge (BPB), the least condyloid-incisor breadth (LCIB), and the breadth of incisor (BI) for PC2, all associated with skull shape (Table 4).
For both morphometric analyses, all the holotypes of nominal taxa under synonym of O. bicolor are included in the morphospace delimited by this species, not overlapping with O. cleberi and Oecomys jamari sp.nov.morphospaces.
The results obtained in our molecular-based tree and in the DFA analyses indicate that Oecomys jamari sp.nov.represents a separate species from O. bicolor lato sensu and O. cleberi lato sensu, sister to the clade formed by the latter two species.Moreover, external morphology, craniodental analyses and our morphometric results presented above show the existence of an exclusive set of traits that support the description of this new species.

Discussion
Our topologies of Cytb þ i7-Fgb recovered Oecomys jamari sp.nov.as a sister species to the clade comprising all the lineages of O. bicolor and O. cleberi.The genetic distance between Oecomys jamari sp.nov.and the O. bicolor and O. cleberi group (3.78%) is lower than values reported for sister species within the genus, such as 4.5% to 6.6% between representative lineages of O. franciscorum and O. mamorae (Pardiñas et al., 2016) and 5.8% between O. tapajinus and O. roberti (Rocha et al., 2018).Altogether, the results of our phylogenetic analyses corroborate that both O. bicolor and O. cleberi represent species complexes, whose species richness and delimitations can only be appropriately defined based on additional molecular and morphological studies.2).
The species herein described contributes to the knowledge of the taxonomy of Oecomys, increasing to 20 species known for the genus.This new species occurs in one of the least known area of endemism located in the Amazon basin, the Rondônia center of endemism, delimited by the Amazon rivers to the north, Tapaj os to the east, and Madeira to the west (Cracraft, 1985).
Regarding sympatry, Oecomys jamari sp.nov.and the northwestern lineage of O. cleberi were both recorded in the municipality of Juruti, state of Par a, and in the Jamari National Forest, Rondônia, reinforcing our hypothesis that these are distinct species.Su arez-Villota et al. (2018) pointed out that sympatry is more common between Oecomys species of distinct body sizes.Nonetheless, the occurrence of sympatry between two species of medium body size was recently reported by Rocha et al. (2014Rocha et al. ( , 2018) ) and Saldanha et al. (2019), and between two smallsized species by Patton et al. (2000), besides the present study.Based on the present study and Su arez-Villota et al. ( 2018), Rocha et al. (2018), Saldanha et al. (2019), andSaldanha &Rossi (2021), we estimate that the new species here described may occur in sympatry also with seven other congeners, such as: the small O. cleberi northern lineage, the medium-sized O. paricola, O. roberti, O. tapajinus, and O. trinitatis, and the large-sized O. catherinae westernmost lineage and O. matogrossensis, which have their distribution overlapping in some degree.
The description of a new species of Oecomys clearly demonstrates the need for continuous inventories and taxonomic studies in the Brazilian Amazonia, even in areas that have been widely deforested, as in the state of Rondônia.It is important to note that the species possibly might be endangered in some degree mainly by the loss of their habitat caused by the expansion of the agricultural frontier in the so-called 'arc of deforestation' of Amazonia, which includes the entire state of Rondônia (Dall'Igna & Maniesi, 2022) and by the existence of two federal roads that cross the Rondônia centre of endemism, which may soon be paved: BR-230 (Transamazonian Highway) and BR-319 (Manaus-Porto Velho Highway).According to Barber et al. (2014), around 95% of all deforestation in the Brazilian Amazonia is located in a strip of 5.5 km along roads and 1 km along rivers, and according to Ferrante et al. (2021), paving roads is the main source of access to unprotected land in the region.Another threat to the species is the weakening of the Brazilian environmental agencies and forest code, which generates expectations of impunity that encourages deforestation acts (Ferrante & Fearnside, 2019), even in well-established protected areas, as observed in the state of Rondônia since 2020 (Messias, M.R., pers.obs.).
Finally, the creation and maintenance of additional protected areas in the Tapaj os-Madeira interfluve is one of the measures needed for Oecomys jamari sp.nov. to be safeguarded, along with many other vertebrates that are endemic to this portion of Amazonia, such as Rondon's marmoset (Mico rondoni) and Prince Bernhard's Titi monkey (Plecturocebus bernhardi).
We thank the Instituto Chico Mendes de Conservac ¸ão da Biodiversidade [ICMBio] also recovered O. cleberi as monophyletic and O. bicolor as polyphyletic based on Cytb sequences, but the species were recovered as reciprocally monophyletic clades in their concatenated data (Cytb þ intron 7 of b-fibrinogen) topology, although specimens of O. bicolor central and western lineages (sensu Su arez-Villota et al., 2018) nested among specimens of O. cleberi.Recently, Brandão et al. (2022) provided compelling evidence of morphological distinction between O. bicolor and O. cleberi, but specimens examined by the authors were restricted to northern clade of O. bicolor and central clade of O. cleberi (sensu Su arez-

Figure 4 .
Figure 4. Map of collection localities of specimens of Oecomys jamari sp.nov., and O. bicolor and O. cleberi lineages included in this study.Stars indicate type localities of Oecomys jamari sp.nov.and the nominal taxa associated with O. bicolor according to Carleton & Musser (2015).Lineages names proposed by Suarez-Villota et al. (2018), and this study (C ¼ central; E ¼ eastern; EC ¼ east-central; N ¼ northern; NC ¼ north-central; NW ¼ northwestern; S ¼ southern; W ¼ western; WM ¼ westernmost).Locality data are provided in Supplemental TableS1.

Figure 8 .
Figure 8. Bayesian Inference topology (BI) based on the mitochondrial Cytochrome b gene of the genus Oecomys.Numbers above the branches indicate Bayesian posterior probabilities number and below the branches indicate maximum likelihood bootstrap values above 50%.Bold numbers indicate the samples of Oecomys jamari sp.nov.Asterisks represent samples analysed molecularly and morphologically.We follow the lineage names proposed by Su arez-Villota et al. (2018), and new lineages named in this study are indicated in bold (C ¼ central; E ¼ eastern; EC ¼ east-central; N ¼ northern; NC ¼ north-central; NW ¼ northwestern; S ¼ southern; W ¼ western; WM ¼ westernmost).Sample data are provided in Supplemental TableS1.

Figure 9 .
Figure 9. Bayesian Inference topology (BI) based on the mitochondrial Cytochrome b gene and nuclear intron 7 b-fibrinogen concatenated of species of the genus Oecomys.Numbers above the branches indicate Bayesian posterior probabilities numbers and below the branches indicate maximum likelihood bootstrap values, above 50%.Bold numbers indicate the samples of Oecomys jamari sp.nov.Asterisks represent samples analysed molecularly and morphologically.We follow the lineage names proposed by Su arez-Villota et al. (2018), and new lineages named in this study are indicated in bold (C ¼ central; E ¼ eastern; EC ¼ east-central; N ¼ northern; NC ¼ northcentral; NW ¼ northwestern; S ¼ southern; W ¼ western; WM ¼ westernmost).Sample data are provided in Supplemental TableS1.
Similarly to previous studies(Saldanha et al., 2019;  Su arez-Villota et al., 2018), the O. bicolor and O. cleberi group was recovered as monophyletic, the central and northwestern O. cleberi lineages appeared as sister clades, and lineages associated to O. bicolor by Su arez-Villota et al. (2018) did not form a monophyletic group in both Cytb and concatenated data topologies.A close relation between the northern O. bicolor clade and the two O. cleberi clades based on Cytb sequences was also reported by Su arez-Villota et al. (2018) and Saldanha et al. (2019), as well as a close relation among the central and western O. bicolor clades and the central and northwestern O. cleberi clades based on concatenated data.This led Saldanha et al. (2019: Fig. 3) to include the central and western O. bicolor clades in their concept of O. cleberi.By adding new samples of specimens of the O. bicolor and O. cleberi species group, our phylogenetic analyses recovered four new lineages, three of which (northern, north-central O. cleberi, and east-central O. bicolor; Figs 8 and 9) are nested in a monophyletic group that includes the two O. cleberi lineages plus either the northern lineage of O. bicolor in the Cytb topology or the central and western lineages of O. bicolor in the concatenated topology.Another new lineage (north-central O. bicolor; Figs 8 and 9) appeared as sister to the southern O. bicolor clade in both topologies.Among the clades recovered in this study, some had very low branch support, as follows: north-central and central O. cleberi in the Cytb topology; east-central O. bicolor in the concatenated topology; and northwestern
a Based on
a Alisphenoid strut present in UFMT1372 and MSF2130.
As previously mentioned by Su arez-Villota et al. (2018), and considering the Cytb and concatenated topologies herein provided, the name O. cleberi Locks, 1981 applies to the central O. cleberi lineage.Considering the Cytb topology and the geographic proximity to the type locality of O. bicolor (Tomes, 1860; see Fig. 4), this may be the name to be associated with specimens of the westernmost O. bicolor clade.The specimens of Oecomys jamari sp.nov.can be distinguished from O. bicolor lato sensu (southern and north-central O. bicolor lineages, plus the specimens MPEG 40734-40735, which forms a monophyletic clade in the Cytb topology) and O. cleberi lato sensu (northern, north-central, northwestern, and central O. cleberi lineages) by craniodental dimensions and external and craniodental morphology.The DFA showed that Oecomys jamari sp.nov.separates completely apart from those taxa in the morphospace and indicated 100% correct classification of Oecomys jamari sp.nov., O. bicolor sensu lato, and O. cleberi sensu lato.Morphologically, Oecomys jamari sp.nov.can be differentiated from its sister taxa by a unique combination of characters (Table

Table 5 .
Coefficient of the first two functions of the Discriminant Function Analysis of adult specimens of Oecomys jamari sp.nov.(n ¼ 4), O. bicolor lato sensu (n ¼ 24), and O. cleberi lato sensu (n ¼ 17) based on 31 craniodental variables.Materials and Methods" section for abbreviations.In bold, the five largest values for each function.
for issuing the collection licence of specimens from Jamari National Forest [no.30902-1].MVB was supported by Fundac ¸ão de Amparo Pesquisa do Estado de São Paulo [FAPESP #10/03969-4].MVB would also like to provide special thanks to RSV for the support with the Collection Study Grant Programme [AMNH].TBFS was supported by a Portuguese Foundation for Science and Technology