Silvio Casadío

The Oyster Crassostrea? hatcheri (Ortmann, 1897), a Physical Ecosystem Engineer from the Upper Oligocene – Lower Miocene of Patagonia, Southern Argentina

Abstract The oyster Crassostrea? hatcheri (Ortmann) is one of the most common fossils in Oligocene–Miocene marine rocks in Patagonia, southern Argentina. This oyster is distinguished by its large size and the great thickness of its valves. It built framework reefs in shallow-shelf environments, and its valves form large biogenic and sedimentologic concentrations exposed in many areas of Patagonia. This paper focuses on the community of boring and encrusting organisms living on the valves of C.? hatcheri, in both the biogenic and sedimentologic concentrations. This community includes fungi, algae, sponges, arthropods, bryozoans, phoronids, polychaetes, brachiopods, and mollusks. The recorded diversity is comparable to that observed in Recent oyster reefs, suggesting that C.? hatcheri was a physical ecosystem engineer in shallow-shelf environments during the late Oligocene–early Miocene. Primary factors in their role as facilitating organisms were, besides the size of the valves, the age of adult specimens (average = 25 years), high population densities, wide geographical range (more than 10° latitude), and long temporal range (more than 5 My), in addition to the framework of the reefs and the sedimentologic concentrations of the valves.

Marine reptiles from the Late Cretaceous of northern Patagonia

Abstract During the Campanian–Maastrichtian, Patagonia was flooded by the Atlantic and reduced to an archipelago. Several localities of northern Patagonia have yielded marine reptiles. Analysis of several assemblages suggests that the diversity and abundance of pelagic marine reptiles in northern Patagonia was higher by the end of the Cretaceous than previously thought. Several plesiosaurids, including Aristonectes parvidens and the polycotylid Sulcusuchus , and the first remains of mosasaurinae have been found. The Cretaceous marine reptile record from South America is scanty. Nevertheless, materials described here suggest that Tethyan and Weddelian forms converged in northern Patagonia, as seen with invertebrates.

MIOCENE FOSSIL DECAPODA (CRUSTACEA: BRACHYURA) FROM PATAGONIA, ARGENTINA, AND THEIR PALEOECOLOGICAL SETTING

ABSTRACT Five previously undescribed decapod taxa have been collected from lower upper Miocene rocks of the Puerto Madryn Formation, Península Valdés region, Chubut Province, Patagonia, Argentina. New species include Osachila valdesensis, Rochinia boschii, Romaleon parspinosus, Panopeus piramidensis, and Ocypode vericoncava. Chaceon peruvianus and Proterocarcinus latus are also reported from the unit, in addition to two indeterminate xanthoid species. Assignment of fossil taxa to genera within the Panopeidae Ortmann, 1893, is difficult due to the marked similarity in dorsal carapace characters among several genera. Panopeus whittenensis Glaessner, 1980, is herein referred to Pakicarcinus Schweitzer et al., 2004. The Puerto Madryn Formation exposed near Puerto Pirámide contains three distinct Facies Associations (1–3), each associated with specific paleoecological and paleoenvironmental conditions, and which recur throughout the section and represent trangressive systems tract (TST) deposits and highstand systems tract (HST) deposits. Within Facies Association 1, near the base of the section at Puerto Pirámide, three paleosurfaces containing invertebrate fossils in life position are exposed and have been carefully mapped in plan view. Because of their sedimentologic, stratigraphic, taphonomic, and paleoecologic features, these three paleosurfaces are considered to be obrution deposits, each preserving a slightly different paleoenvironmental regime in terms of water depth and position with respect to wave base. Paleosurfaces were formed during the waning stages of the transgressive systems tract.

40Ar/39Ar age and oxygen isotope temperature of the Centinela Formation, southwestern Argentina: An Eocene age for crustacean-rich “Patagonian” beds

Abstract The presence of a prominent volcanic ash enclosed within sediments of the Centinela Formation, southwestern Argentina, permits establishment of an 40Ar/39Ar age of approximately 46 Ma for these rocks. Oxygen isotopic analysis of shell material from the oyster Crassostrea? hatcheri Ortmann, 1897 , suggests seasonal fluctuation of temperature from about 15°C to about 21°C. In concordance with this, a diverse crustacean fauna, including nine families within the order Decapoda and one within Isopoda, bears strong affinities with temperate and subtropical faunas of the Atlantic Ocean basin and documents the southernmost extension of low latitude oceanographic influence on this region during the Paleogene. Establishment of an Eocene age for the rocks in the Centinela Formation provides the first definitive documentation of rocks of that age in the region of Calafate, permits correlation of these rocks with Eocene strata southward to the vicinity of Rio Turbio, and suggests that these rocks, assigned to the Patagonian sequence, may be substantially older than those in eastern Argentina.

Record of Late Miocene glacial deposits on Isla Marambio (Seymour Island), Antarctic Peninsula

Abstract We report and describe two new small diamictite outcrops on Isla Marambio (Seymour Island), Antarctic Peninsula. These rocks rest on an erosional unconformity on top of the Eocene La Meseta Formation and are unconformably covered by glaciomarine rocks of the ?Pliocene–Pleistocene Weddell Sea Formation. The lithology, fossil content and isotopic ages obtained strongly suggest that the rocks belong to the Hobbs Glacier Formation and support a Late Miocene age for this unit. Additionally, the dated basalt clast provides the oldest age (12.4 Ma) for the James Ross Island Volcanic Group recorded up to now. The here described diamictite cannot be confidently correlated with a glaciomarine unit previously assigned to the Late Eocene–Lower Oligocene taken as proof that initial expansion of ice on Antarctica encompassed the entire continent synchronously in the earliest Oligocene. However, it is now evident that there are likely to be more, short but important, stratigraphic sequences of key regional and Antarctic wide interest preserved on the plateau of Isla Marambio.

West Antarctic Rift System: A Possible New Zealand-Patagonia Oligocene paleobiogeographic Link

merous shared taxa. Twenty two mollusk genera appearing in South American Late Oligocene–Miocene rocks are recorded also in New Zealand, but making their first appearance there in older rocks (Deminucula, Notolimopsis, Glycymeris (Glycymerula), Cyclochlamys, Gonimyrtea, Spissatella, Scalpomactra, Turia, Crosseola, Sigapatella, Trichosirius, Sassia zealta group, Ataxocerithium, Penion, Nassarius (Hima), Xymenella, Austromitra, Zeacuminia, Eoturris, Neoguraleus (Fusiguraleus), Oamaruia (Oamaruia), and Opimilda. At the same time, 16 taxa appear in South America in rocks older than those containing these taxa in New Zealand (Zygochlamys, Tiostrea, Aulacomya, Lucinoma, Antisolarium (from Valdesia), Xymene, ?Trophon, Provocator, Antimelatoma, Solemyarina, Anadara, Mytilus, Protothaca, Diloma, Argobuccinum, Fusitriton). At the same time (Late Oligocene–Early Miocene), eight genera appear in both areas (Neopanis, Austrovenus (from Ameghinomya), Cirsotrema (large species), Oamaruia (Zeadmete), Puyseguria, Cosa, Notolimea, Lamprodomina (Beu et al., 1997). Bryozoans recorded from around the Oligo

Un nuevo hadrosáurido (Dinosauria, Ornithopoda) de la Formación Allen, Provincia de La Pampa, Argentina

Abstract. A NEW HADROSAURID (DINOSAURIA, ORNITHOPODA) FROM ALLEN FORMATION, LA PAMPA PROVINCE, ARGENTINA. New studies of a Hadrosauridae specimen collected in the Allen Formation, Late Campanian/Early Maastrichthian from La Pampa Province, Argentina, allow recognizing a new taxon, Lapampasaurus cholinoi gen. et sp. nov., which is diagnosed by the following combination of characters: anterior cervical vertebrae with lateral foramina on the dorsal side of the diapophyses, scapula with laterally sharp deltoid crest and convex dorsal surface, pedal ungual phalanx longer than wide with superficial grooves and foramina, and shallow, longitudinal ventral ridge. The identification of Lapampasaurus as a member of Hadrosauridae is confirmed by the recognition of several synapomorphies, such as cervical neural arches with zygapophysial peduncles that elevate above the neural canal, long and dorsally arched postzygapophyses, coracoid relatively small when compared with the scapula, with concave anterior margin and well developed bicipital knob, and hoof-shaped pedal ungual phalanx. The record of Lapampasaurus in the Late Cretaceous of Patagonia suggests the presence of a more diverse hadrosaurid fauna than previously recorded.

Mass Mortality Of Fossil Decapods Within the Monte LeóN Formation (Early Miocene), Southern Argentina: Victims Of Andean Volcanism

Abstract Four exposed planar surfaces within the type area of the Monte León Formation (early Miocene) of southern Patagonia, Argentina, enclose significantly different fossil assemblages positioned in close geographic and stratigraphic proximity to one another. The exposed paleosurfaces were mapped in planar view using a quadrat grid system. Precise fossil position and orientation data, stable isotope thermometry and petrographic analyses, and petrologic and taphonomic evidence suggest an inner-shelf, shallow water habitat, above storm wave base, with a well-oxygenated benthos and weak offshore bottom currents. The rate of sedimentation was generally low, interspersed with periods of non-deposition and sporadic, higher-energy pulses of sediment input. Stable isotope analyses of foraminiferans indicate bottom water temperatures consistent with a modern mid-latitude coastal setting. Two distinctly different assemblages were observed: 1) a relatively diverse, normal marine benthic fauna consisting of bivalves, gastropods, bryozoans, echinoids, and decapods; and 2) a unique assemblage consisting solely of numerous, exceptionally preserved, fully-articulated crabs. These assemblages occur in a one meter interval within the lower-most beds of the Monte León Formation. The occurrence and preservation of large numbers of decapods within the fossil record are rare, making these deposits remarkable. The crab-rich assemblage was stratigraphically positioned below the surfaces containing the normal marine assemblage. The crabs are contained within a slightly compacted, argillaceous volcanic tuff, consisting mostly of volcanic glass shards and euhedral plagioclase grains. Biogenic fragments are noticeably absent from the deposit, unlike sediments collected from the upper surfaces. Most of the crabs were preserved with their third maxillipeds in an open, gaping posture. This is consistent with postures observed in extant crabs suffering from respiratory distress. From the above evidence it is inferred that the fossil crabs were suffocated, killed, and rapidly buried. Supradjacent layers record the re-establishment of normal marine conditions. The apparent faunal disparity observed on the four paleosurfaces within the Monte León Formation is interpreted as representing the initial decimation and eventual re-establishment of the benthic marine fauna following a catastrophic volcanic event.

New Miocene Decapoda (Thalassinidea; Brachyura) from Tierra del Fuego, Argentina: Paleobiogeographic Implications

ABSTRACT A decapod crustacean fauna of Tierra del Fuego, Argentina, is documented from the middle Miocene Carmen Silva Formation and the early? Miocene Cerro Águila Conglomerate of the Cabo Domingo Group. Three new genera and five new species are named: Asthenognathus australensis, new species; Miotymolus quadratus, new genus and species; Mursia fuegiana, new species; Pharkidodes agele, new genus and species; and Tierrapilumnus edseli, new genus and species. Compilation of all described species of decapods from late Oligocene to early Pliocene exposures in 18 general localities in Patagonia, southern Argentina, and Chile documents two paleobiogeographic provinces, Argentine and Chilean. Coupled with evidence from the biogeographic patterns of associated mollusks, the faunas from Tierra del Fuego have been assigned to the Argentine Paleobiogeographic Province. Comparison of the distribution of Miocene decapods with that of extant decapods (Boschi 2000) leads to the conclusion that the thermal separation of South Atlantic and South Pacific water in the Miocene was more pronounced than today, so that there is no evidence of a discrete Magellanic Biogeographic Province characterizing the high southern latitude region during the Miocene.

Upper Cretaceous–Paleocene echinoids from northern Patagonia, Argentina

Abstract Echinoids are among the most conspicuous and diverse constituents of the Upper Cretaceous and Paleocene marine invertebrate fauna of Argentina. Nine species were collected from localities exposing the Jagüel (Maastrichtian), Roca (Maastrichtian– Danian), Salamanca (Danian), Arroyo Barbudo (Danian), El Fuerte (Danian), and Arroyo Salado (Danian) Formations in northern Patagonia, Argentina. Only one of these taxa, Paraster joannisboehmi (Oppenheim in Böhm, 1903), has been described previously from Argentina. Four taxa, Gauthieria menuthiae (Lambert and Savin in Lambert and Thiéry, 1911), Nucleopygus pullatus (Stoliczka, 1873), Diplodetus nutrix (Lambert in Boule, 1899), and Hemiaster hawkinsi Lambert, 1933, have been described previously from Madagascar. One species, Micropsis desori (Cotteau in Leymerie and Cotteau, 1856), has been described previously from France. One taxon, Pygopistes parrasae is a new species. Argentinian cassiduloids include the only two known Danian species of Nucleopygus and Pygopistes. The spatangoids were not strongly affected by the K-T extinction event. Comparisons of the Patagonian echinoids with those of the Northern Hemisphere indicate that they were strongly influenced by dispersal from Tethyan sources.