Cerradomys, 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 : 8-10

Cerradomys , new genus

TYPE SPECIES: Hesperomys subflavus Wagner, 1842 .

CONTENTS: maracajuensis Langguth and Bonvincino, 2002 ; marinhus Bonvincino, 2003 ; scotti Langguth and Bonvincino, 2002 (including andersoni Brooks et al., 2004); and subflavus Wagner, 1842 (including vulpinus Lund, 1840; vulpinoides Schinz, 1845; and laticeps Winge, 1888 [not Lund, 1840]).

DISTRIBUTION: In dry tropical and subtropical forests of the Caatinga, Cerrado, and Chaco from northeastern Brazil to eastern Bolivia.

MORPHOLOGICAL DIAGNOSIS: Dorsal pelage coarsely grizzled, usually some shade of reddish- or yellowish-brown; ventral pelage abruptly paler in some species (superficially whitish or yellowish) or not (the ventral coloration merging gradually with that of the dorsum), but ventral hairs always gray-based. Pinnae small, not extending to 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 dI–dV; plantar surface densely covered with distinct squamae distal to thenar pad; hypothenar pad small but distinct; claw of dI extending beyond middle of phalange 1 but not quite to first interphalangeal joint of dII; claw of dV extending to but not beyond first interphalangeal joint of dIV. Tail longer than combined length of head and body, weakly bicolored in most species but distinctly bicolored in others (e.g., C. scotti ).

Skull with long, tapering rostrum flanked by deep zygomatic notches; interorbital region anteriorly convergent, with strongly beaded supraorbital margins; braincase oblong, with well-developed temporal crests; lambdoidal and nuchal crests well developed in older adults. Posterior margin of zygomatic plate usually anterior to M1 alveolus. Jugal present but small (maxillary and squamosal zygomatic processes overlapping in lateral view but not in contact). Nasals not extending posteriorly beyond lacrimals; lacrimals usually sutured equally to maxillary and frontal bones (except in C. maracajuensis , which has longer maxillary than frontal sutures). Frontosquamosal suture usually colinear with frontoparietal suture. Parietals with broad lateral expansions. Incisive foramina long, usually extending posteriorly to or between M1 alveoli; usually widest at midlength and tapering symmetrically anteriorly and posteriorly. Posterolateral pits large, complex, and recessed in deep fossae; mesopterygoid fossa penetrating anteriorly between maxillae but usually not between molar rows; bony roof of mesopterygoid completely ossified in some species (e.g., C. marinhus and C. maracajuensis ) but perforated by large sphenopalatine vacuities in others (e.g., C. scotti ). Alisphenoid strut absent (buccinator-masticatory foramen and accessory foramen ovale confluent) in most species, but present (foramina separate) in C. scotti . Stapedial foramen and posterior opening of alisphenoid canal vestigial or absent; squamosal-alisphenoid groove and sphenofrontal foramen absent; secondary anastomosis of internal carotid crosses dorsal surface of pterygoid plate (5 carotid circulatory pattern 3 of Voss, 1988). Postglenoid foramen large and rounded; small subsquamosal fenestra distinct and patent in most species but absent or vestigial (not patent) in C. scotti . Periotic exposed posteromedially between ectotympanic and basioccipital but usually not extending anteriorly to carotid canal; mastoid completely ossified or fenestrated (variation observed within and among species). Capsular process of lower incisor alveolus strongly developed below base of coronoid process; superior and inferior masseteric ridges converge anteriorly as open chevron below m1.

Labial and lingual flexi of M1 and M2 not 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, usually separated from anterocone by persistent anteroflexus; protostyle usually absent; paracone connected by enamel bridge to middle or to posterior moiety of protocone. Second upper molar (M2) protoflexus present; mesoflexus usually present as two internal fossettes. Third upper molar (M3) with posteroloph; hypoflexus present or absent. Accessory labial root of M1 present.

First lower molar (m1) anteroconid without an anteromedian flexid; anterolabial cingulum present on all lower molars; anterolophid present on m1 but absent on m2 and m3; ectolophid usually absent on m1 and m2; mesolophid well developed on m1 and m 2 in most species, but mesolophid (and mesostylid) reduced or absent in C. scotti ; m2 hypoflexid short. Accessory lingual and labial roots present 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 posterior spinous process. Supratrochlear foramen of humerus present.

Stomach without extension of glandular epithelium into corpus. Distal bacular cartilage of glans penis bifid (the central digit is vestigial or absent); nonspinous tissue on crater rim does not conceal bacular mounds; dorsal papilla spineless; urethral processes without subapical lobules.

COMPARISONS: Cerradomys was represent- ed by ‘‘ Oryzomys ’’ subflavus in the phylogenetic analyses of Weksler (2003, 2006), who consistently recovered it as a member of clade D (as in fig. 1 ). Although its phylogenetic position within clade D was never strongly supported in any analytic permutation based on morphological and/or IRBP sequence characters, Cerradomys never appeared as the sister taxon of any other species of Oryzomys sensu lato. However, it is phenetically most similar to Aegialomys (the ‘‘ xanthaeolus group’’ of authors), Oryzomys sensu stricto (the ‘‘ palustris group’’), and Sooretamys (‘‘ Oryzomys ’’ angouya ). Comparisons with Oryzomys are provided here, whereas comparisons with Aegiolomys and Sooretamys are provided in the accounts for those taxa (above and below, respectively).

Cerradomys differs from Oryzomys sensu stricto by its distinct hypothenar pad on the hind foot (the hypothenar is absent or vestigial in Oryzomys ); conspicuous tufts of long ungual hairs at the bases of the claws on pedal digits II–V (the short ungual hairs of Oryzomys do not form distinct tufts); lacrimals that are usually sutured equally to the maxillary and frontal bones (the lacrimals are primarily sutured with the maxillaries in Oryzomys ); shorter palate (the mesopterygoid fossa does not extend anteriorly between the maxillary bones in Oryzomys ); absence of an anterolophid on m2 and m3 (the anterolophid is distinct on unworn m2 and m 3 in Oryzomys ); presence of an anapophysis on the fifth lumbar vertebra (absent in Oryzomys ); bifid distal bacular cartilage (the distal bacular cartilage is trifid in Oryzomys ); dorsal papilla of glans penis spineless (spinous in Oryzomys ); and urethral processes without subapical lobules (present in Oryzomys ).

REMARKS: Compelling evidence for the monophyly of Cerradomys is provided by parsimony and maximum likelihood analyses of cytochrome b mtDNA sequences ( Bonvicino and Moreira, 2001; Bonvicino, 2003). The highly distinctive anatomy of the glans penis, which lacks a central bacular digit, likewise supports this conclusion. Hopefully, the flurry of recently published descriptions of new species of Cerradomys (e.g., by Langguth and Bonvicino, 2002; Bonvicino, 2003; Brooks et al., 2004) will soon be followed by more synthetic and comprehensive studies to convincingly document species identifications and geographic distributions across the entire range of this obviously diverse clade. At least some of the many unstudied specimens representing this genus from Bolivia and Paraguay are likely to belong to taxa recently described from Brazilian material, but others may represent new forms. Unfortunately, no taxonomic study published to date has effectively transcended national boundaries.

ETYMOLOGY: For the Cerrado, a vast mosaic of savannas and dry forests, where many species of this clade are found.

Figures

Fig. 1. Phylogenetic relationships of oryzomyines based on a heuristic parsimony analysis of sequence data from the Interphotoreceptor Retinoid Binding Protein (IRBP, 1266 bp from exon 1) and 99 morphological characters (after Weksler, 2006: fig. 37). Numbers above and below branches represent jackknife support (.50%) and decay indices (.1), respectively. Vertical bars on the right-hand side of the figure indicate taxon membership in clades A–D. See Weksler (2006: 14–17) for methodological details.