CRETACEOUS CALCAREOUS NANNOFOSSILS AND BIOSTRATIGRAPHY OF SOUTHEASTERN AUSTRAL BASIN, PATAGONIA, ARGENTINA. This study presents the results of a quantitative analysis of the calcareous nannofossils recovered in five localities in the southeastern sector of the Austral Basin. On the basis of the assemblages recovered and its comparison with previous biozonations for the Austral Atlantic Ocean, it was possible to identify Valanginian—early Hauterivian, early Albian—middle Albian, late Albian—Cenomanian, Coniacian/Santonian—Campanian and late Maastrichtian assemblages. Two discontinuities evidenced by biostratigraphical hiatuses for the Cretaceous sequence were deduced: one for the late Hauterivian—Barremian and the other for at least the Turonian. The Early Cretaceous assemblages are comparable to those of the Falkland Plateau and they would be developed on an external platform having cold surface waters and high availability of nutrients. The Late Cretaceous assemblages are similar to those found in the Neuquina and Colorado basins and they would be developed on an internal platform having cold to temperate surface waters.

A REVISION OF THE GENUS ABDERITES AMEGHINO, 1887 (MARSUPIALIA, PAUCITUBERCULATA). In this contribution, a taxonomic review for the genus Abderites Ameghino is presented. A comparative morphological analysis of the teeth, including a review of the dental homology, was performed. The continuous quantitative characters were evaluated by means of a traditional morphometric analysis. As a result, three species were recognized for the Miocene of Argentina and Chile. From the eight species originally described by Ameghino, only A. crispus Ameghino from the Colhuehuapian (early Miocene) of Argentina, and A. meridionalis Ameghino from the “Pinturan” and Santacrucian (late early Miocene) of Argentina, are considered valid species. In addition, this study allowed identification a new species, Abderites aisenense sp. nov., recorded in the Friasian s.s. and Colloncuran (middle Miocene) from Chile and Argentina respectively. A. pristinus (Ameghino) previously recognized as valid species, is considered nomen dubium.

CONODONT BIOSTRATIGRAPHY OF THE UPPERMOST SAN JUAN FORMATION AND THE LOWER MEMBER OF LOS AZULES FORMATION AT CERRO LA CHILCA, SAN JUAN PRECORDILLERA. The present contribution deals with a conodont association in the uppermost San Juan Formation and the lower member of the Los Azules Formation at the Cerro La Chilca section, Central Precordillera. The presence of key conodonts such as Eoplacognathus pseudoplanus (Viira), Histiodella kristinae Stouge and Microzarkodina sp. cf. M. ozarkodella Lindström suggests upper part of the E. pseudoplanus Zone. This is the first record of a conodonts association in the lower member of the Los Azules Formation. The biostratigraphic significance of “Bryantodina ” aff. typicalis Stauffer is discussed. The middle Darriwilian E. pseudoplanus Zone is introduced for the Middle Ordovician biostratigraphic chart of the Precordillera. This zone is equivalent with at least the top of the Paroistodus horridus Subzone (Lenodus variabilis Zone), E. psuedoplanus/ D. tablepointensis Zone, and H. kristinae Subzone (E. suecicus Zone).

DEFINITION OF THE GENUS EUMYSOPS AMEGHINO, 1888 (RODENTIA, ECHIMYIDAE) AND SYSTEMATICS OF THE SPECIES FROM THE EARLY PLIOCENE OF CENTRAL ARGENTINA A definition of the genus Eumysops Ameghino and a systematic review of its oldest species, E. laeviplicatus Ameghino and E. formosus Ameghino, from the early Pliocene of the Monte Hermoso and “Irene” Formations (southwest of Buenos Aires province, central Argentina), are provided. Eumysops has craniomandibular and postcranial features that clearly define it within the Echimyidae: posterior skull short and bowed, rostrum narrow, orbital region very wide, paroccipital apophysis ventrally protruding, condyle and coronoid processes low, distalized ventrocaudal iliac spine, and metatarsals I, II and V markedly reduced. According to the concept of Eumysops here proposed, the genus would include four species: E. laeviplicatus, E. formosus, E. chapalmalensis Rovereto y E. gracilis Rovereto species. The oldest species E. laeviplicatus, from the Montehermosan—lower Chapdamalalan, co-occurs with E. formosus at least in the lower Chapadmalalan. These species are absent in the early—late Pliocene of the Chapadmalal area (southeast of Buenos Aires province) where other representatives of the genus are recorded. This stratigraphic pattern, concurrent with that of other two caviomorph genera, supports the hypothesis that there is a higher faunal similarity between the two recognized levels of the Monte Hermoso Formation than between the upper level of this formation and the Chapadmalal Formation.

BRYOPHYTE ASSOCIATION FROM THE LA CANTERA FORMATION, LATE APTIAN, SAN LUIS BASIN, ARGENTINA. The La Cantera Formation (Early Cretaceous) has yielded an important palynoflora associated to a diverse macroflora; both recovered from rocks exposed at its type locality in the Sierra del Gigante, San Luis Basin, central-western Argentina. Spores of the genera Aequitriradites (Delcourt and Sprumont) emend. Cookson and Dettmann and Couperisporites Pocock are described and illustrated together with diverse plant morphotypes recovered from the same fossiliferous levels and belonging to Bryophyta, albeit not in organic connection. This new analysis of the fossil plant association (disperse spores and macroscopic remains) reveals a dominance of spores and megaflora with hepatic affinity within the bryophytes. The occurrence of spores and macroremains of hepaticae and mosses in the same sediments suggests the in situ development of this group of plants (there is no evidence of transport). They grew in this part of the San Luis Basin during the Aptian under local wet conditions related to a fresh water body.

The described indeterminate boid snake was collected in rocks belonging to the Sarmiento Formation and exposed at La Gran Hondonada (Chubut Province, Argentina). This is the first snake record for the mid—late Eocene Mustersan South American land-mammal age. The specimen proves that medium- to large-sized boids inhabited the Patagonian region during most of the Palaeogene, suggesting climatic conditions warmer than those established at the beginning of the Neogene.

A NEW SPECIES OF RHEA (AVES: RHEIDAE) FROM THE LATE MIOCENE OF THE MESOPOTAMIA IN ARGENTINA. A new species of rhea, Pterocnemia mesopotamica sp. nov. (Aves: Rheidae), from the late Miocene of Mesopotamia in Argentina is described. Specimens come from the base of the Ituzaingó Formation (= “Conglomerado osífero” or “Mesopotamiense”), which crops out along the cliffs of the Paraná river near the homonimous city in Entre Ríos Province. Pterocnemia mesopotamica sp. nov. is a slender and small-bodied bird, similar in size to the lesser rhea or choique (P. pennata), and characterized by the marked divergence of the tarsometatarsal trochleae. Fragmentary remains of a femur and a humerus, identified as Rheidae indet., are also reported from the same locality and horizon. An isolated tarsometatarsus, coming from the Aisol Formation in Mendoza Province, is referred to Pterocnemia cf. P. mesopotamica sp. nov. If this record is confirmed, the biochron of the new taxon would extend back from the late Miocene (Huayquerian Age) to the middle Miocene (Friasian Age).

KIPUTZ IX: A UNIQUE ASSEMBLAGE OF STEPPE BISON (BISON PRISCUS BOJANUS, 1827) REMAINS FROM THE UPPER PLEISTOCENE OF THE IBERIAN PENINSULA. Kiputz IX is an upper Pleistocene site that has provided the richest set of steppe bison remains in the Iberian Peninsula. This paper provides a metric study of the postcranial skeleton of 18 individuals that conform this tafocenosis. The comparison with other European sets, near in space and time, allows the attribution of this material to the subspecies Bison priscus mediator Hilzheimer. The robustness index of the metacarpus diaphysis indicates the existence of a clear sexual dimorphism and a balance between sexes within the sample. The stage of dental substitution makes evident that the sample is dominated by juvenile and subadult specimens, with a low proportion of adult individuals. The absolute chronology of the remains and its association with an important sample of reindeer confirm that the preferential biotope of this species was the steppe. The bison sample from Kiputz IX constitutes a good basis for comparative studies of large bovid populations from middle and upper Pleistocene of Europe.