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Anatomical comparative studies including myological data of caviomorph rodents are relatively scarce, leading to a lack of use of muscular features in cladistic and morphofunctional analyses. In rodents, the hip adductor muscles constitute an important group of the hindlimb musculature, having an important function during the beginning of the stance phase. These muscles are subdivided in several distinct ways in the different clades of rodents, making the identification of their homologies hard to establish. In this contribution we provide a detailed description of the anatomical variation of the hip adductor muscle group of different genera of caviomorph rodents and identify the homologies of these muscles in the context of Rodentia. On this basis, we identify the characteristic pattern of the hip adductor muscles in Caviomorpha. Our results indicate that caviomorphs present a singular pattern of the hip adductor musculature that distinguishes them from other groups of rodents. They are characterized by having a single m. adductor brevis that includes solely its genicular part. This muscle, together with the m. gracilis, composes a muscular sheet that is medial to all other muscles of the hip adductor group. Both muscles probably have a synergistic action during locomotion, where the m. adductor brevis reinforces the multiple functions of the m. gracilis in caviomorphs. Mapping of analyzed myological characters in the context of Rodentia indicates that several features are recovered as potential synapomorphies of caviomorphs. Thus, analysis of the myological data described here adds to the current knowledge of caviomorph rodents from anatomical and functional points of view, indicating that this group has features that clearly differentiate them from other rodents. [ABSTRACT FROM AUTHOR]

Abstract: First records of continental vertebrates from the upper levels of the Paraná Formation (Late Miocene) at La Juanita locality, Entre Ríos Province (Mesopotamia, Argentina), are reported and evaluated from chronological, paleobiogeographical, and paleoenvironmental perspectives. Among caviomorph rodents, caviids, hydrochoerids, and the extinct octodontoid Plesiacarechimys are described. The pampatheriid Scirrotherium sp. and a phoenicoptherid bird are identified. A “pre-Huayquerian” age (older than 8.7 Ma) is proposed for the fossil bearing levels. The “Paranense Sea”, one of the most widespread Middle-Late Miocene Atlantic transgressions that covered southern South America, is interpreted as an important geographical barrier promoting vicariance of the Plesiacarechimys lineage. Cavioids recovered from the Paraná Formation represent the first stages of the radiation of these rodents at the latitude of Entre Ríos Province in the context of the whole South American subcontinent. The genesis of the fossiliferous level corresponds to a storm deposit in a littoral marine environment. Capybaras and flamingos suggest the presence of water bodies, saline lagoons, mudflats, or shallow brackish coastal or inland lakes, in accordance with the geological data of the Paraná Formation. [Copyright &y& Elsevier]

The Santa María-Hualfín Basin was proposed as a regional synchronous lithostratigraphic depocenter in the geological province of Northwestern Pampean Ranges, Northwestern Argentina. However, new 40 Ar– 39 Ar dating indicates that deposits toward the east, in Santa María Valley (Santa María Department), are younger than the western depocenter in San Fernando (Belén Department). Therefore, it would be more appropriate to study these valleys as separate basins, each one with its own tecto-sedimentary features. The east basin, named in this paper Villavil-Quillay, constitutes an elongated independent basin that developed along the front of the eastern Puna bordering with Papachacra and Durazno Ranges. This basin is composed of more than 3000 m of mudstone, sandstone, conglomerates, volcaniclastic and pyroclastic deposits. Villavil-Quillay basin develops onto a peneplain of Precambrian and lower Cambrian rocks, most of which are metamorphic and granites rocks. The sedimentary fill consists of Cretaceous? and Cenozoic continental deposits. The Cenozoic record is composed of a) the Santa María Group (Miocene-Pliocene), formed by Las Arcas, Chiquimil, Andalhuala and Corral Quemado Formations, and b) the Punaschotter unit (Puna's Gravels in German, Pleistocene). This study involves the Andalhuala, Corral Quemado and Punaschotter deposits cropping out in San Fernando area. The set of identified facies assemblage corresponding to the Andalhuala Formation shows a vertical variation of fluvial sub-environments, varying from permanent sandy braided rivers to gravel rivers and aeolian dunes culminating in an alluvial dry cycle. While facies assemblages of the Corral Quemado Formation allow inferring the development of ephemeral water bodies from secondary channels on the floodplain, the Punaschotter conglomerates indicate the development of gravel channels and bars. Three samples of tuffs interbedded in the sedimentary levels of Andalhuala Formation were dated indicating that the Miocene-Pliocene boundary is represented in this area. The lower tuff beds, outcropping at the southwest of San Fernando Sur, provided an age of 5.59 ± 0.04 Ma (late Miocene, Messinian). The others tuffs beds, both outcropping at the west-northwest of San Fernando Norte and overlaying the first one, gave an age of 4.79 ± 0.15 Ma and 4.72 ± 0.08 Ma (early Pliocene, Zanclean), respectively. These absolutes ages, together with the results of a sedimentological analysis, indicate that westward from San Fernando River, much of the areas mapped as Corral Quemado Formation correspond to the Andalhuala Formation; while part of the area considered as Punaschotter unit must be assigned to Corral Quemado Formation. Also, a thick tuff bed, recognized at the contact of Corral Quemado and Punaschotter , was considered as the previous one dated in 3.66 Ma, in Puerta de Corral Quemado locality. [ABSTRACT FROM AUTHOR]

Northwestern Argentina contains one of the most complete continental late Neogene (ca. 9–2.58 Ma) fossiliferous sequences in South America, especially in the current territories of the Catamarca, Tucumán and Jujuy provinces. More precisely in Jujuy Province several localities bearing mainly fossil mammals have been reported at the Quebrada de Humahuaca in the Uquía, Maimará and Tilcara formations, in which the clade Xenarthra (Mammalia) is well-represented. In this scenario, the fossiliferous potential of other localities of Jujuy Province are less known, especially in those areas located at the northwest end of Argentina, bordering Bolivia in the Northern Puna. A new late Neogene fossiliferous locality near Calahoyo (3639 m.a.s.l), Jujuy Province, is here reported. The materials, belonging to Xenarthra, were exhumed from the base of the Tafna Formation which was deposited in a sedimentary basin by alluvial and/or fluvial currents, undergoing transitions of various lacustrine episodes. The taxa include the Tardigrada Pyramiodontherium bergi (Megatheriidae) and the Cingulata Eosclerocalyptus sp. (Glyptodontidae) and Macrochorobates chapalmalensis (Dasypodidae). From a biostratigraphic viewpoint, this assemblage suggests a Late Miocene-Pliocene age for the base of the Tafna Formation, and partially contradicts the supposed Plio-Pleistocene age of this unit. Finally, the new specimens here described indicate that Xenarthra were taxonomically and ecologically diverse during the late Neogene in the northwest end of Argentina, since they are represented by at least three main lineages (sloths, glyptodontids and armadillos). [ABSTRACT FROM AUTHOR]

The best known Neotropical fossil bufonid discovered to date is described herein. This material includes well-preserved cranial and postcranial disarticulated remains that were part of a microvertebrate fossil assemblage generated by the accumulation of predatory bird pellets. The remains were recovered from the Middle Unit of the Uquía Formation (late Pliocene) that crops out next to the locality of Humahuaca, Jujuy Province, northwestern Argentina. In this contribution, we present a detailed osteological description of this taxon and compare the morphological characters with respect to other related members of the large genus Rhinella. Several distinctive character states present in these fossil remains allows us to refer to them as part of a new species of the Andean R. spinulosa Group. The new species described here together with the fossil marsupials and sigmodontines rodents suggest that by the late Pliocene, the Uquía area, the Andean region of Bolivia, and southern Peru were part of the same biogeographic unit. • A microvertebrate fossil assemblage from the Middle Unit of the Uquía Formation (late Pliocene) was studied. • The best known Neotropical fossil bufonid anuran discovered to date is described as a new species of Rhinella. • The new toad species would have lived in open environments under dry climatic conditions. [ABSTRACT FROM AUTHOR]