Euryoryzomys, WEKSLER & PERCEQUILLO & VOSS, 2006

WEKSLER, MARCELO, PERCEQUILLO, ALEXANDRE REIS & VOSS, ROBERT S., 2006, Ten New Genera of Oryzomyine Rodents (Cricetidae: Sigmodontinae), American Museum Novitates 3537 (1), pp. 1-29 : 11-14

Euryoryzomys , new genus

TYPE SPECIES: Oryzomys macconnelli Thomas, 1910 .

CONTENTS: emmonsae Musser et al., 1998 ; lamia Thomas, 1901 ; legatus Thomas, 1925 ; macconnelli Thomas, 1910 (including incertus J.A. Allen, 1913, and mureliae J.A. Allen, 1915); nitidus Thomas, 1884 (including boliviae Thomas, 1901 ); and russatus Wagner, 1848 (including physodes Brants, 1827, intermedia Leche, 1886, coronatus Winge, 1887, kelloggi Ávila-Pires, 1959 , and moojeni Ávila-Pires, 1959).

DISTRIBUTION: In moist (evergreen and semi-evergreen) forests throughout the cis- Andean tropical and subtropical lowlands of South America, including Amazonia, the Guianas, southeastern Brazil, eastern Bolivia, northern Argentina, and eastern Paraguay (see Musser et al., 1998: figs. 78, 79).

MORPHOLOGICAL DIAGNOSIS: Dorsal pelage finely grizzled yellowish- to reddish-brown; ventral pelage abruptly paler (superficially whitish), but ventral hairs always gray-based. Pinnae large, reaching eye when laid forward. Mystacial and superciliary vibrissae not extending posteriorly beyond pinnae when laid back. Hind foot with conspicuous tufts of long ungual hairs at bases of claws on dII–dV; plantar surface smooth or sparsely covered with indistinct squamae distal to thenar pad; hypothenar pad distinct; claw of dI extending just beyond base of phalange 1 of dII; claw of dV extending to middle of phalange 1 of dIV. Tail about as long as combined length of head and body in some species (e.g., E. nitidus ) but usually longer than head and body in others (e.g., E. macconnelli ); distinctly bicolored (dark above, pale below).

Skull with long, tapering rostrum flanked by deep zygomatic notches; interorbital region anteriorly convergent, with beaded supraorbital margins; braincase oblong, with weakly developed temporal crests; lambdoidal and nuchal crests developed in older adults. Posterior margin of zygomatic plate usually dorsal to M1 alveolus; jugal present but small in most species, but absent in E. lamia . Nasals not extending posteriorly beyond lacrimal bones in some species (e.g., E. macconnelli ) but often extending beyond lacrimals in others (e.g., E. lamia ); lacrimals equally sutured to maxillaries and frontals. Frontosquamosal suture usually colinear with frontoparietal suture. Parietals without lateral expansions in some species (e.g., E. russatus ) or lateral expansions present but usually not very broad (e.g., in E. macconnelli ). Incisive foramina ranging from moderately short and posteriorly broad (e.g., in E. macconnelli ) to moderately long and widest near their midlength (e.g., in E. russatus ), but never extending posteriorly between M1 anterocones. Posterolateral palatal pits small to moderately large, but usually not recessed in distinct fossae; mesopterygoid fossa extending anteriorly between maxillae in some species (e.g., E. russatus ) but not in others (e.g., E. macconnelli ); bony roof of mesopterygoid fossa completely ossified or perforated by small (slit-like) sphenopalatine vacuities. Alisphenoid strut usually absent (buccinator-masticatory foramen and accessory oval foramen confluent) in most species but often present in others (e.g., E. nitidus ). Stapedial foramen, squamosal–alisphenoid groove and sphenofrontal foramen present (5 carotid circulatory pattern 1 of Voss, 1988). Postglenoid foramen large and round- ed, subsquamosal fenestra large and patent. Periotic exposed posteromedially between ectotympanic and basioccipital, but usually not extending anteriorly to carotid canal; mastoid completely ossified in most fully adult specimens. Capsular process of lower incisor alveolus well developed in adult specimens of most species but absent in E. macconnelli and E. emmonsae ; superior and inferior masseteric ridges converge anteriorly as open chevron below m1.

Labial and lingual flexi of M1 and M2 not (or shallowly) interpenetrating. First upper molar (M1) anterocone not divided into labial and lingual conules (anteromedian flexus absent); anteroloph well developed and fused with anterostyle on labial cingulum, separated from anterocone by persistent anteroflexus; protostyle absent; paracone connected by enamel bridge to posterior moiety of protocone except in E. macconnelli (where the attachment is usually to the middle of the protocone). Second upper molar (M2) protoflexus present; mesoflexus usually present as two internal fossettes. Upper third molar (M3) without posteroloph; hypoflexus well developed (persisting with moderate to heavy wear: e.g., in E. lamia ) or absent (e.g., in E. nitidus ). Labial accessory root of M1 usually absent.

First lower molar (m1) anteroconid without an anteromedian flexid; anterolabial cingulum present on all lower molars; anterolophid present on m1 but usually absent on m2 and m3; ectolophid variably present or absent on m1 and m2; mesolophid well developed on m1 and m2; m2 hypoflexid short. Accessory roots usually absent on m1; m2 and m3 each with one large anterior root and one large posterior root.

Fifth lumbar (17th thoracicolumbar) vertebra with well-developed anapophysis. Hemal arch between second and third caudal vertebrae with or without posterior spinous process. Supratrochlear foramen of humerus present.

Stomach without extension of glandular epithelium into corpus. Male accessory reproductive glands not dissected, unknown. Distal bacular cartilage of glans penis large and trifid (with robust central digit); shelf of nonspinous tissue on crater rim does not conceal bacular mounds; dorsal papilla spineless; urethral processes without subapical lobules.

COMPARISONS: Weksler’s (2003, 2006) phylogenetic analyses of morphological and molecular characters consistently recovered Euryoryzomys (represented by ‘‘ Oryzomys ’’ lamia , ‘‘ O. ’’ macconnelli , and ‘‘ O. ’’ russatus ) as a member of clade B together with Hylaeamys , Transandinomys , Nephelomys , Oecomys , Handleyomys , and the ‘‘ alfaroi group’’. Within clade B, however, the relationships of Euryoryzomys were not consistently indicated by different analytic permutations. Whereas some analyses suggested that this genus may be the sister group of Mindomys + Oecomys , others recovered it as a basal lineage or as the sister group of Transandinomys , but none of these alternatives was strongly supported. Phenetically, Euryoryzomys resembles other lowland moist-forest taxa that also have large pinnae, short outer digits on the hind foot, and that normally lack accessory roots on M1/m1. Comparisons of Euryoryzomys with Hylaeamys and Transandinomys are of special interest because the species that we assign to these genera have traditionally been treated as members of the so-called ‘‘ capito ’’ complex of Oryzomys sensu lato ( Musser et al., 1998).

Although fully adult specimens of Euryoryzomys are usually larger than those of Hylaeamys (see measurement data summarized by Musser et al., 1998) and tend to have brighter (tawny or ochraceous versus brownish) dorsal fur, these genera are externally similar and are often confused in the field. Among the integumental contrasts summarized by Musser et al. (1998: table 52), tail coloration most consistently distinguishes Euryoryzomys (their ‘‘ nitidus group’’) from Hylaeamys (their ‘‘ megacephalus ’’ and ‘‘ yunganus ’’ groups): In Euryoryzomys , the tail is almost always distinctly bicolored, whereas it is indistinctly bicolored or unicolored (alldark) in Hylaeamys .

Euryoryzomys also differs strikingly from Hylaeamys by its primitive pattern of carotid circulation (pattern 1 of Voss, 1988), which includes both the supraorbital and infraorbital branches of the stapedial artery. The supraorbital branch leaves a prominent translucent groove across the squamosal and alisphenoid on the inside of the braincase and exits the skull via the sphenofrontal foramen; both of these osteological features are lacking in Hylaeamys , amost all specimens of which clearly lack the supraorbital branch of the stapedial artery (pattern 2 of Voss, 1988). Illustrations of these alternative conditions as expressed by representative species of Euryoryzomys and Hylaeamys are provided in Musser et al. (1998: fig. 27).

The only other cranial trait that usefully distinguishes these genera is mastoid fenestration. The occipital surface of the mastoid capsule that houses the paraflocculus is completely ossified in almost all examined specimens of Euryoryzomys , but it is prominently fenestrated in most specimens of Hylaeamys . Illustrations of these contrasting character states, exemplified by other taxa but resembling the conditions seen in Euryoryzomys and Hylaeamys , are provided in Weksler (2006: fig. 22).

Fully adult specimens of Euryoryzomys average larger than those of Transandinomys , but they are otherwise similar in most external features. Indeed, the integumental pigmentation of T. talamancae strikingly resembles that of Euryoryzomys . Apparently, the only nonmetric external feature by which Euryoryzomys and Transandinomys can be distinguished is the length of the superciliary vibrissae. These tactile hairs, rooted just above the eye, extend well behind the pinnae in both species of Transandinomys , although they are much longer in T. bolivaris than in T. talamancae (see Musser et al., 1998: fig. 53). By contrast, the superciliary vibrissae do not extend beyond the posterior margins of the pinnae in examined specimens of Euryoryzomys .

Euryoryzomys and Transandinomys also differ in several dental traits. Of these, the most striking concerns the upper second molar (M2) mesoflexus, which is consistently represented by two internal fossettes (labial and medial) in Euryoryzomys , whereas only a single internal fossette represents the M2 mesoflexus in Transandinomys (see Musser et al., 1998: figs. 29, 151). On the upper third molar (M3), the hypoflexus tends to be deeper and more persistent in Euryoryzomys than it is in Transandinomys , but this trait is not sufficiently constant to permit unambiguous identifications by itself. On the second lower molar (m2), however, the hypoflexid is distinctively shorter in Euryoryzomys (see Musser et al., 1998: fig. 32A,B) than it is in Transandinomys (see Musser et al., 1998: fig. 64, left and middle).

REMARKS: This clade has usually been called the ‘‘ nitidus group’’ by authors (e.g., Weksler, 1996; Musser et al., 1998; Percequillo, 1998; Patton et al., 2000), but we designate macconnelli as the type species of Euryoryzomys because it is represented by more complete character data than any of the other congeneric forms whose relationships have been analyzed to date. Although only three of the species that we refer to Euryoryzomys were analyzed by Weksler (2003, 2006), more taxonomically inclusive phylogenetic studies based on morphological data also support generic monophyly ( Weksler, 1996). This clade is likewise recovered by parsimony analyses of cytochrome b sequence data that exclude third-position transitions and by neighbor-joining and maximum-likelihood analyses when transversions are weighted more heavily than transitions ( Bonvicino and Moreira, 2001).

ETYMOLOGY: From eurus (Greek for farreaching or far-spread), in reference to the extensive distribution of this genus.