Graomys

Abstract: Phylogenetic relationships and species limits within the South American rodent genus Phyllotis were estimated using nucleotide sequence data from a 973 base-pair region of the mitochondrial gene, cytochrome b . Geographic variation and species limits were assessed by sequencing individuals from multiple populations and morphometric analyses of skulls and skins. Results supported the following clades: Phyllotis plus Auliscomys exclusive of Graomys , the darwini species group, and a northerly distributed species-pair of P. amicus and P. andium . The phylogeny, genetic divergence estimates, and morphology indicated that P. xanthopygus rupestris is polyphyletic and populations from the Pacific slope of the Andes currently assigned to that taxon are specifically distinct. These populations are placed in the newly elevated P. limatus and an emended diagnosis is provided. Biogeographic and phylogenetic patterns are most consistent with successive colonization of the Pacific slopes by P. xanthopygus , possibly through range expansion and contraction, over a short period of time relative to the age of the clade.

Abstract: A new genus of phyllotine rodent is described. One species from northwestern San Luis Province and southeastern San Juan Province, Argentina is included. This new genus is compared with species of Eligmodontia, Calomys, Andalgalomys , and Graomys . External, cranial, and dental characters indicate that the new genus is most closely related to Calomys and Eligmodontia . The new genus may be distinguished using both quantitative and qualitative characters. The discovery of a new genus of Sigmodontine rodent specialized for desert environments in Argentina is the second in 15 years and underscores the need for further faunal work in arid areas of South America.

Abstract: Resumen. Se estudiaron aspectos taxonomicos y paleoambientales de un agregado de micromamiferos coleccionado en sedimentos pleistocenicos de Ramallo (33° 29’ S, 60° 01’ O, partido de Ramallo, provincia de Buenos Aires). Los sedimentos portadores pueden referirse a la parte superior de la Formacion Ensenada (Piso Ensenadense, Biozona de Tolypeutes pampaeus) con una edad algo mas joven que 0,78 Ma. Se registraron los siguientes roedores Sigmodontinae: Akodon cf. A. azarae (Fisch.), Necromys cf. N. benefactus (Thos.), Scapteromys cf. S. aquaticus-S. tumidus, Oligoryzomys cf. O. flavescens (Waterh.), Calomys cf. C. laucha-C. musculinus, Graomys cf. G. griseoflavus (Waterh.), Reithrodon auritus (Fisch.) y un genero indeterminado. La composicion taxonomica del agregado de Ramallo robustece la hipotesis que la estructura especifica de las comunidades vivientes de sigmodontinos se alcanza, en la region pampeana, durante el Ensenadense. Un analisis integral de las evidencias paleobiologicas del perfil de Ramallo indica la transicion entre condiciones calidas y humedas hacia otras frias y secas. Las primeras son sugeridas por el desarrollo de una comunidad caracteristica de bosques de Celtis tala Gill. ex Planch. similar a la que se verifica actualmente en Ramallo. Condiciones frias y secas son evidenciadas por el registro de marmosinos y roedores extralocales de afinidades centrales y patagonicas (e.g., Lestodelphys sp., Microcavia sp.) y la ausencia de C. tala. Este cambio climatico se verifica por arriba del limite Matuyama-Brunhes, indicando un desacople entre la reversion paleomagnetica y el deterioro ambiental en el norte de la provincia de Buenos Aires. Abstract. SIGMODONTINE RODENTS (MAMMALIA: RODENTIA: CRICETIDAE) AND OTHER MICROMAMMALS FROM NORTHERN BUENOS AIRES PROVINCE (ARGENTINA): PALEOENVIRONMENTAL RECONSTRUCTION FOR THE UPPERMOST ENSENADAN. We studied taxonomical and paleoenvironmental aspects of a micromammal assemblage recovered from Pleistocene sediments in Ramallo (33° 29’ S, 60° 01’ W, Ramallo county, Buenos Aires province). The bearing sediments can be referred to the uppermost part of the Ensenada Formation (Ensenadan Stage, Biozone of Tolypeutes pampaeus) aged little younger than 0.78 Ma. The following sigmodontine rodents were recorded: Akodon cf. A. azarae (Fisch.), Necromys cf. N. benefactus (Thos.), Scapteromys cf. S. aquaticus-S. tumidus, Oligoryzomys cf. O. flavescens (Waterh.), Calomys cf. C. laucha-C. musculinus, Graomys cf. G. griseoflavus (Waterh.), Reithrodon auritus (Fisch.), and an unidentified genus. The Ramallo assemblage supports the hypothesis that the specific structure of modern sigmodontine fauna in Buenos Aires province was settled during the Ensenadan. An integral analysis including all the biotic evidences collected in the Ramallo section (rodents, marsupials, plant macrofossils, mollusks, and insects) indicates a transition from wet and warm conditions to dry and cold ones. The former conditions are suggested by the development of a Celtis tala Gill. ex Planch. wood, similar to those presently occurring in Ramallo area. The latter conditions are evidenced by the record of extralocal Central-Patagonian marmosines and rodents (e.g., Lestodelphys sp., Microcavia sp.) and the absence of C. tala. This environmental and climatic change took place above the Matuyama-Brunhes boundary, at the end of the Ensenadan stage, indicating a delay between the paleomagnetic reversion and the environmental deterioration in northeastern Buenos Aires province.

Abstract: Ornithodoros quilinensis sp. nov. (Acari: Argasidae) is described from larvae collected on the small rodents Graomys centralis (Cricetidae: Sigmodontinae) in Argentina. The diagnostic characters for this new species are a combination of small size (520–540 μm), a dorsal plate oval in shape with a length of approximately 200 μm, 14 pairs of dorsal setae, hypostome short and narrower at the base (length from Ph1 to apex 133 μm (120–141)) with dental formula 2/2 and apex blunt, and the capsule of the Haller’s organ irregular in shape and without reticulations. The analysis of the 16S rDNA sequences available for the genus Ornithodoros indicate that, phylogenetically, O. quilinensis represents an independent lineage only related to a Bolivian tick species of the genus Ornithodoros yet not formally described.