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Articulated fossil ophiuroids from South America were reported for the Devonian, Cretaceous, Eocene, and Miocene. Here we report the first Jurassic record of an articulated ophiuroid from the Sierra Chacaicó Formation (early Pliensbachian-Sinemurian) in Neuquén Basin, Argentina, and discuss the taphonomic processes that allowed its preservation. The Sierra Chacaicó Formation represents the onset of the Early Jurassic extensive marine transgression in the basin. The basal section comprises shoreface and offshore Gilbert-type delta system, which was affected by hyperpycnal discharges. The middle and upper sections are represented by offshore deposits, affected by storms and eroded by hyperpycnal channel-levee systems. The ophiuroid specimen was found in levels of massive, fine, tuffaceous sandstone beds and covered by coarse sandstone containing a large amount of plant debris and organic matter. It was preserved articulated, with a complete disc and almost complete arms. Based on the microstructure of the spine-bearing lateral arm plates, the ophiuroid is assigned to Sinosura, an extinct genus of the family Ophioleucidae, widespread in the Lower Jurassic deposits of Europe but previously unknown from other parts of the world. The posture of the ophiuroid, with one arm curved distally and extended in one direction and the other four arms symmetrically oriented in the opposite direction, suggests a walking or escape movement frozen in time. This implies that the ophiuroid was buried alive by sediment thick enough to prevent successful escape. The taphonomic and sedimentologic evidence indicates that the fossil material was found in hyperpycnal deposits accumulated in offshore positions, which carried a high concentration of sediment in suspension. [ABSTRACT FROM AUTHOR]

Three relatively complete elasmosaurid plesiosaurs were recently recovered from the north of Patagonia, Argentina. They were found in the uppermost levels of the Jagu¨el Formation (upper Maastrichtian). One of the specimens was found only 0.3 m below the Cretaceous/Paleogene boundary, this being the youngest record of a Mesozoic reptile in Patagonia. Two specimens are referred to cf. Mauisaurus sp. and the other to Tuarangisaurus? cabazai sp. nov. This study has revealed that some character states, previously regarded as mere ontogenetic variations, could be taxonomically valid. Comparison of the Upper Cretaceous elasmosaurids of Patagonia with those from the Upper Cretaceous of central Chile, the northeastern islands of the Antarctic Peninsula, and New Zealand reinforce the hypothesis of a south Gondwanan distribution for some pelagic reptiles. [Copyright &y& Elsevier]

The fossil record of chondrichthyans in Argentina is still poorly known. The aim of the present contribution is to describe teeth representing a chondrichthyan assemblage from Man Aike Formation (late Eocene) exposed in the Lago Argentino area, at Santa Cruz province, Argentina. This report includes Striatolamia macrota, Macrorhizodus praecursor, Carcharias sp., a possible member of the family Pristiophoridae, for the Argentine territory. Previous Eocene reports of Striatolamia macrota from Argentina are based on incorrect determination of specimens. The shark association, especially the abundance of lamniforms, may be indicative of litoral and shallow (less than 30 m depth) temperate to cold waters, as suggested by micropaleontological content. • For the first time a late Eocene chondrichthyan assemblage is described from Santa Cruz province, Argentina. • Striatolamia macrota , Macrorhizodus praecursor , Carcharias sp., and Pristiophoridae are reported. • Species here described are frequent in fish faunas from the North Atlantic seas. [ABSTRACT FROM AUTHOR]

Abstract: The San Julián and Monte León formations (“Patagonian”) are exposed along the Atlantic coast of Patagonia, whereas in the west equivalent rocks are known as Centinela Formation. Sixteen 87Sr/86Sr measurements on the oyster Crassostrea? hatcheri (Ortmann) from the San Julián and Centinela formations and an 40Ar/39Ar-date from a whole-rock sample from the Centinela Formation yielded ages that allow more precise correlation between the two areas. 87Sr/86Sr measurements from the San Julián Formation yielded ages between 23.83 and 25.93Ma, while for the Centinela Formation the ages ranged between 21.24 and 26.38Ma. The 40Ar/39Ar analysis of a sample of the Centinela Formation yielded an age of 20.48±0.27Ma. The age data suggest a late Oligocene (Chattian) age for the San Julián Formation and the lowermost beds of the Centinela Formation (northernmost exposures). The Monte León Formation along the East coast and the entire section of the Centinela Formation in the southern area – and the middle and upper beds of this same unit in the northernmost localities – were deposited at the end of the Oligocene and early Miocene (Chattian–Burdigalian). The invertebrate fauna present in these units shows diverse preservation patterns that makes these fossils, especially the mollusks, not useful – at this stage – for correlation purposes. [Copyright &y& Elsevier]