A NEW SPECIES OF RETISPIRA KNIGHT (GASTROPODA, BELLEROPHONTOIDEA) FROM THE LOWER PERMIAN OF CHUBUT PROVINCE, ARGENTINA. A new species of Retispira Knight (Gastropoda, Bellerophontoidea) from the lower Permian of the Tepuel-Genoa Basin, Chubut Province, Argentina, is described. The specimens come from the Cisuralian Euphemites chubutensis - Palaeoneilo aff. concentrica Zone. Retispira patagoniensis sp. nov. is a small, subglobose, phaneronphalus bellerophontid characterized by having a broad selenizone with fine lunulae and spiral lirae. Spiral and colabral elements generate a reticulate pattern. The new species developed in both shallow marine and deltaic facies and its distribution was mainly affected by water turbidity, depth and temperature. Its feeding habit may have been herbivorous, probably as an algal foliage dweller.

TAPHONOMY OF THE NEOSAUROPOD NESTING SITE FROM SANAGASTA (LA RIOJA, ARGENTINA): EXCEPTIONAL PRESERVATION IN A CRETACEOUS HYDROTHERMAL PALEOENVIRONMENT. The Cretaceous Sanagasta nesting site, La Rioja Province, Argentina, has shed insights on the reproductive behavior of neosauropods, documenting colonial behavior, phylopatry, and an opportunistic environment-dependent-reproduction relationship with their paleoenvironment. The taphonomy of this monotypic nesting site is described in order to assess its biostratinomy and fossil diagenesis. The 3D spatial egg-clutch arrangement is well preserved and suggests the presence of autochthonous associations with in-situ ovipositions, without nesting trace. The egg-bearing level presents a matrix-supported packed biofabric and an “intrinsic” biogenic accumulation that implies a gregarious behavior through their preferential colonization of a specific paleohydrothermal nesting site. The biocenosis of biogenically deposited eggs, with eggshell mineralization is altered by hydrothermal activity, and extremophile microorganisms. The thanatocenosis and time-averaging were virtually null because the eggs buried in the substrate immediately after being laid. In contrast, the taphocenosis represents the most important taphonomic feature. The eggshells display several synchronous taphonomic alterations produced by acidic hot spring solutions, while re-calcification and silicification are the most common eggshell recrystallizations. The presence of microchert, chalcedony, ∼10 μm-diamteer opal-A microspheres, epidote aggregates, several macro-structures, and fibrous clay minerals replacing parts of the eggshell and egg membranes, indicates an extreme hydrothermal alteration under exceptional conditions. The presence of fossil stromatolites, cyanobacterians, and diatoms, coupled with sedimentary structures (microfacies and hydrothermal microfabrics), and with eggs taphonomy imply that the Sanagasta nesting site represents a particular instance of taphocenosis and a Lagerstätte. The Sanagasta dinosaur nesting site is the first documented case of environment-dependent reproduction amongst neosauropods.

THE YANGTZEPLACOGNATHUS CRASSUS (CONODONTA) ZONE, DARRIWILIAN OF THE CENTRAL PRECORDILLERA, SAN JUAN, ARGENTINA. Elements of Yangtzeplacognathus crassus (Chen and Zhang) were recovered from samples collected in the San Juan Formation at three section in the Central Precordillera, San Juan Province, Argentina. The last meters of the San Juan Formation are exposed at the Quebrada del río de Las Chacritas, Cerro La Chilca and Quebrada Del Aluvión where these gray limestone strata are represented by grainstone, packstone-wackestone y dolopackstone. These limestone outcrops correspond to different carbonate ramp facies, from distal ramp, middle ramp, and lagoon. The key conodont Yangtzeplacognathus crassus documents the Yangtzeplacognathus crassus Zone in these sections, pointing towards a middle Darriwilian age for the conodont-bearing strata in the San Juan Formation and allowing correlation among these sections. The middle Darriwilian biostratigraphic frame of Baltica and central-south China is verified for the argentine Precordillera.

The brachiopod fauna from the San Benito Formation of Bolivia, of late Sandbian—Katian age, is re-studied on the basis of material collected in the Cordillera del Tunari. The new heterorthid genus Tunaria is erected to include the species Orthis berthoisi? var. erratica Davidson, 1869 (formerly attributed to Drabovinella) from England, France and Spain, and the new species Tunaria cocksi from Bolivia. The fauna also includes the first record in South America of Rafinesquina pseudoloricata (Barrande), and Hirnantia cf. transgrediens (Havlíček). Overall, the low diversity San Benito fauna corroborates the Mediterranean biogeographic signature of Central Andean brachiopod assemblages.

PHYTOLITH ANALYSIS OF TEZANOS PINTO FORMATION (LATE PLEISTOCENE-HOLOCENE) IN THE SOUTHWESTERN REGION OF ENTRE RÍOS PROVINCE (ARGENTINA). Loess deposits are the main component of the Late Quaternary sequences of the Pampa plains (South America). The Last Glacial Maximum loess represents a depositional unit of the Pampean Aeolian System that evidences the expansion of semiarid conditions to the northeast of the region. The Tezanos Pinto Formation is the typical loessic unit of the late Pleistocene—early Holocene of the northeastern Pampa region. Advances in the knowledge of the micropaleobotanical content of this geologic formation are presented in this work, especially the obtained results of the Southweastern area of Entre Ríos Province. The analyzed phytolith assemblages show a high homogeneity with some variations that allowed their quantitative differentiation across the analyzed sedimentary profiles. The presence of grass phytoliths jointly with palm, podostemoid and ciperoid elements allowed to make this characterization. The described phytolith assemblages, as previously observed in the northwestern part of the area covered by the loess in Entre Ríos, show high abundance of megathermic grasses, with a greater presence of xeric elements at lower levels, and with elements denoting warm-temperate episodes with major moisture principally in their middle and top sections. This is linked to the presence of a warm-temperate to temperate steppe with xeric conditions in the basal levels.

A description is provided for Wolfestheria smekali gen. and sp. nov., a new member of the family Fushunograptidae, from the “Estancia La Sin Rumbo” locality in the Puesto Almada Member of the Cañadón Asfalto Formation. Assignment to the family Fushunograptidae is supported by evidence from detailed scanning electron microscope studies of this species. An assessment of the complex carapace ornamentation is also provided, as W. smekali exhibits an array of ornamentations that cover the entire carapace surface. These consist of irregular, thick radial lirae with numerous thin cross-bars on the dorsal middle-upper third of the carapace, changing to straight, thick radial lirae with fewer cross-bars restricted to the upper half of the growth band in the ventral third of the carapace, with the interspaces between the radial lirae wider than the lirae themselves, and with the radial lirae terminating in the upper part of the growth bands, where they then enlarge to form a triangular shape upon contact with the following growth line. These characteristics allow us to compare W. smekali with the eosestheriid genera Yanjiestheria Chen and Abrestheria Wang, as well as with the other fushunograptids from the Upper Jurassic to Lower Cretaceous of China such as Cratostracus Huang and Qinghaiestheria Wang. W. smekali is also comparable to fushunograptids and related forms from the Jurassic system of Argentina. The occurrence of W. smekali correlates biostratigraphically with the “Eosestheriopsis dianzhongensis fauna” of China, as well as with other Jurassic faunas from Africa and Europe. This correlation supports a Late Jurassic age for these fossiliferous assemblages (Puesto Almada Member, Cañadón Asfalto Formation) from the province of Chubut, Argentina.

The non-mammalian therapsids dominated the terrestrial ecosystems during the Late Paleozoic—Early Mesozoic. The cynodonts have been studied from a taxonomic, osteologic and morphological perspective. However, taphonomy using chemometrics has been barely explored. This report includes a rib and an appendicular bone of cynodonts from the Puesto Viejo Group (Mendoza, Argentina). These fossils are studied for the first time using SEM-EDX. Semi-quantitative data derived from SEM-EDX spectra is evaluated by principal component analysis to gain new insights regarding the different diagenetic pathways of bone microstructure. The multivariate model supports the distinction of different sampled areas (bone, transition zone and rock matrix), in terms of chemical parameters. Differentiation is based mainly on varying contents of Ca, P, F, Si, Al, K, O, Mn and Fe. Variable concentrations of Fe and Mn could be related to different facies (floodplain and crevasse splay). These results along with thin section petrographical analysis confirm —in one of the cases— the substitution of hydroxyapatite by fluorapatite in the bone microstructure. Fossil-diagenetic processes observed herein include substitution, fracturing, brittle deformation and different permineralization events. Permineralization stages during burial history include infilling of vascular canals, trabeculae and fractures with hematite, manganite and calcite. The presence of calcite and iron enrichment indicates local reducing conditions below water-table during precipitation. This chemometric approach to the study of Triassic cynodont remains proved useful for assessing the chemical changes in bone microstructure.