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= Limaysaurus = Limaysaurus (“Limay lizard”) was a genus represented by a single species of rebbachisaurid sauropod dinosaurs, which lived during the mid-Cretaceous period, about 99.6 and 97 million years ago, in the Cenomanian, in what is now South America.

Description
Limaysaurus was a medium-size sauropod that reached 18 meters in length, 6 m in height, and 18 tonnes in weight. The neural spine in cervical and dorsal vertebrae is not V- shaped but it has a simple and straight form like an I. Its teeth were curved, unlike those teeth of Diplodocus which were flatter. Another distinct characteristic of this sauropod is its close relationship to Rebbachisaurus from Morocco. This discovery supports the theory that there was a possible land bridge connection between South America and Africa 100 million years ago. It shared its habitat with Andesaurus and Giganotosaurus, characterized by plains with shallow lagoons. The climate was mild and humid. In fossil remains of Limaysaurs gastroliths were found, which were used to help the stomach to grind food.

History and classification
Limaysaurus was found 15 km southwest of Villa El Chocón, Picún Leufú Department, in Neuquén, Argentina. The sediments belong to the Subgroup Río Limay, in Lohan Cura Formation, at Cerro Aguada del León. It was originally named Rebbachisaurus tessonei, a species of the African dinosaur, but in 2004 Salgado et al. used different genera. This discovery shed some light on the distribution of Gondwanan dinosaurs in the mid-Cretaceous period. Several specimens of Limaysaurus are known, one of which is 80% complete.

Limaysaurus is a sauropod of the family Rebbachisauridae, with a close affinity with the African genera Rebbachisaurus and Nigersaurus, and the south American genera Rayososaurus and Cathartesaura. The name of this species comes from Río Limay which borders the region and from the most complete specimen first discovered by Lieto Tessone.

= El Juncal Lagoon = El Juncal Lagoon was an important body of water located near the city of Viedma. It was approximately 60 km long and 4 km wide, running parallel to Río Negro with a separation of between 6 and 7 km. Being a supply of animal and vegetable food, it was an area which was inhabited by different populations. The vestiges of those civilizations are important archaeological sites that have been analyzed by many researchers since the 19th century.

Recent history
After a severe flood in 1899 causing havoc in Viedma and surrounding areas, several projects were analyzed to control the course of the river and overflowing of the lagoon.

During the 1930's, the lagoon was drained in order to prevent flooding in the area, improve the way people from neighboring towns communicated, and use the land for agricultural production.

Settlements
The shores of the lagoon were settled by people approximately 3,000 years ago. The vestiges of those settlements drew the first naturalists' attention who visited the region on expeditions during the 19th century. Mass graves (cemeteries) explain the exploitation of the lagoon by different populations.

After the lagoon was drained, while the land was prepared for crop production, many human corpses were discovered. In 1970 a team lead by Rodolfo Casamiquela made plaster casts out of skeletons. Those burials were replicated in order to be exhibited in different local museums of Río Negro, meeting the museological standards of that time. One of them was sent to Museo Provincial Carlos Ameghino in Cipolletti, and it was later lent to Museo Estación Cultural, in Fernández Oro.

Lithology
In its type locality, the Roca Formation is divided into three sections. The first section, that is, the base, is approximately 20 m thick (66 ft). It consists of intercalated bioclastic limestones and green claystones. The calcareous materials are highly fossiliferous with textures like wackestone and packstone without an obvious orientation of the shells. The claystones are composed of montmorillonite with calcite and quartz. The second section (middle) is not over 8 m thick (26 ft) and consists mainly of limestones. Such section has very thin strata of varied yellow limestones and siltstones, interbedded with yellow porous and coarse-grained limestones. The limestones of the middle section are almost devoid of fossil invertebrates. The third section (upper) is 25-30 m thick (82-98 ft). It is mainly composed of white gypsum in large crystals. It has lenticular intercalations of greenish siltstones with wave-formed ripples and fragments of gypsum.

The faunal data on the fossils of marine invertebrates in the Roca Formation suggests a transgression from the Atlantic Ocean. By contrast, the marine invasions in Argentina and Chile during the Jurassic and Early Cretaceous were caused by an ingression from the Pacific Ocean.

Discovery of fossils
The first section of the Roca Formation has abundant fossiliferous content, including bivalves, gastropods, bryozoans, echinoderms, crustaceans, ostracods, foraminifera, and calcareous nanoplankton, as well as remains of fish.

Bivalves
Pycnodonte (Phygraea) burckhardti (Boehm),

Pycnodonte (Phygraea) sarmientoi Casadío 1998,

Gryphaeostrea callophyla (Ihering),

Ostrea wilckensi Ihering,

Ostrea neuquena Ihering,

Cubitostrea ameghinoi (Ihering),

Nucula (Leionucula) dynastes Ihering,

''Neilo cf. N. ornata'' (Sowerby),

Cucullaea rocana Ihering,

Chlamys patagonensis negroina Ihering,

Musculus rionegrensis (Ihering),

Arca ameghinorum Ihering (=Venericardia ameghinorum),

Venericardia iheringi (Boehm),

V. feruglioi Petersen,

Aphrodina burckhardti (Ihering),

Gastropods
“Aporrhais” spp.,

Turritella Turritella burckhardti Ihering,

''Turritella aff. T. malaspina'' Ihering,

Nautoloids
Hercoglossa romeroi (Ihering),

Cimomia camachoi Masiuk,

Decapods
Callianassa burckhardti Boehm,

Echinoida
Linthia joannisboehmi Oppenheim,

Nucleopygus salgadoi Parm

Area distribution
The main outcrops of the Jagüel Formation are found in the inner sectors of the Neuquén Basin, where the "Rocanense Sea" reached its maximum depth. In the Andean region, it crops out in the south of Mendoza, where its fossil content dates back to the age Maastrichtian. In the area of Huantraico (Neuquén), the Jagüel Formation crops out at Cerro Villegas, where it is 23 m thick (75 ft).

Moreover, its outcrops are partially covered in the eastern flank of Añelo low (sector Lomas Coloradas–sierras Blanca), in the surrounding area of Pelligrini Lake, in the hills to the north of Río Negro extending to General Roca. Having reduced outcrops, it can be observed in the surroundings of Casa de Piedra reservoir. Due to its fine and homogeneous lithology, its outcrops have few morphological features and they are often partially covered.

Lithology
The Jagüel Formation consists of monotonous olive green and yellowish mudrocks (claystones, siltstones, mudstones), traversed by thin veins of fibrous gypsum. These veins are found on the meteorized surface and they give distinct brightness to the outcrops. The claystones are plastic and friable, with waxy brightness. Some of them are laminated, while the siltstones are grayish.

With these distinct characteristics, it crops out in its type locality (Jagüel de Rosauer) and at Lomas Coloradas, where the unit is 18–26 m thick (59–85 ft). The outcrops around Pelligrini Lake keep the typical characteristics of the unit. Olive green calcareous mudrocks appear in the northern sector of the lake, which are solid and friable with fragmentary remains of molluscs (oysters). In this sector, there is also abundant fossil content composed of scallops and small brachiopods. Besides, there is an important microfaunal assemblage from the mid–Maastrichtian. In this area, it has a maximum thickness of 30 m (98 ft).

In the hills located in the north of General Roca (type locality of the Roca Formation), the outcrops of the Jagüel Formation are very friable, and they are covered by rock fragments from upper layers of the same unit. They are brown–olive. They make up the base of the hills and have the typical aspect of this unit. The boundary with the overlying Roca Formation is marked by yellowish resistant limestones.

Finally, the lower part of the Jagüel Formation crops out above the southern margin of Casa de Piedra reservoir. It is composed of brown–ochre mudrocks, with many veins of gypsum at the base, and a thin layer of highly fossiliferous limestones that lies 1 m (3 ft) above its contact with the Allen Formation. The outcropping thickness of the unit is 25 m (82 ft). Dark brown friable mudstones crop out above the northern shore of the reservoir, with remaining molluscs in the lower part, near the shore. In the upper section, there are ochre mudrocks which are gypseous, and its outcrops are partially covered; there, its thickness is 20 m (66 ft). In this sector, the Jagüel Formation is covered unconformably by the Vaca Mahuida Formation.

In the area of Huantraico, there are greenish calcareous mudstones, with thin intercalations of calcareous sandstones; the mudstones are solid or laminated. The lithofacies characteristics of the unit suggest an outer continental shelf environment, below the normal wave base.

Age and correlations
The micropaleontological content of the Jagüel Formation made it possible to classify it as Maastrichtian–Danian (Early and Late). This formation conformably overlies the Allen Formation and it also conformably underlies the Roca Formation. The Pircala–El Carrizo Formation lies above these formations. All of them belong to the Malargüe Group.

Microfossils
The Jagüel Formation, aged Maastrichtian and Danian, constitutes the peak of the transgression within the Malargüe Group, reaching maximum depths of a mid–outer shelf environment. It has abundant marine microfossils, such as planktonic and benthic foraminifera, calcareous ostracods and nannofossils, as well as dinoflagellates. Generally, they are well preserved. The micropaleontological record of the Jagüel Formation is of paramount importance since this unit contains the Cretaceous–Paleogene bounda ry in different localities, which marks the Cretaceous–Paleogene (K–Pg) extinction event.

Reptiles
The record of faunal marine reptiles include mosasaurs and the marine turtle Euclastes meridionalis.

Macroinvertebrates
As a result of a taxonomic revision of the Cretaceous–Paleogene (K–Pg) oysters in the Neuquén Basin, in the west of Argentina, it was mentioned that there were Pycnodonte (Phygraea) vesicularis, Amphidonte mendozana, Ostrea wilckensi, Gyrostrea lingua, Ambigostrea clarae, and Gryphaeostrea callophyla.

Moreover, it was observed that there were other specimens, like bivalves, gastropods, irregular echinoids, bryozoans, and decapods.

Environment
The Jagüel Formation contains marine deposits accumulated in inner positions of the basin, with depths that vary from a mid to an outer continental shelf. Sedimentological and paleontological evidence suggests a predominance of normal atmospheric conditions, below the normal wave base and with optimal circulation, away from the sources of detritus supply.

Discovery
This notosuchian was found in the locality of La Buitrera in the late 1990's, in the Candeleros Formation (Cenomanian–Turonian). These outcrops are located 30 km of Cerro Policía, Río Negro (northwest Patagonia). The faunal assemblage of this locality includes dryolestids, theropods, crocodyliforms, snakes, sphenodontians, and fragmentary remains of frogs and fish. The Candeleros Formation, in Neuquén, was characterized by a diverse fauna that included titanosaurian and diplodocoid sauropods, carcharodontosaurid theropods, chelid turtles, pipoid anurans, and the crocodyliform Araripesuchus patagonicus. However, the fauna of La Buitrera is different from other types of fauna, including abundant fossils of small vertebrates. The term Buitreraensis refers to the place where the specimen was found, that is, in the locality of La Buitrera.

Taxonomy
The species Araripesuchus buitreraensis shares phylogenetic characteristics with the clade Araripesuchus. The diagnostic characteristics that make this species different from others of the same genus are its pterygoid flanges, which are pneumatic and poorly expanded at its lateral end. Another characteristic is its transversely elongated depression on the ventral surface of the pterygoid flanges, which is close to the posterior margin of the suborbital fenestra. The specimen found in La Buitrera (MPCA-Pv 235), which belongs to the holotype of the species, is considerably different from all known specimens of Araripesuchus patagonicus. For example, in the species A. patagonicus, the frontal does not extend into the supratemporal fossa, and the parietal and postorbital come into contact extensively within this opening. In the specimen MPCA-Pv 235, however, the frontal extends widely into the supratemporal fossa, and reaches the margin of the supratemporal fenestra. Therefore, the parietal and postorbital do not come into contact. As regards the general form of the brain of Araripesuchus buitreraensis, it resembles closely that of the species Araripesuchus wegeneri, and differs significantly from that of Alligator and Anatosuchus. Although its cerebral hemispheres are less compressed dorsoventrally than in the African species, the sinus that separate them is well marked. This phylogenetic analysis shows that Araripesuchus is a basal clade of mesoeucrocodylians. The South American taxons are more similar to each other than the species Araripesuchus wegeneri which lived in Africa during the Early Cretaceous.

Age and stratigraphy
The Malargüe Group ranges in age between Campanian (Late Cretaceous) and Danian (Paleogene period). It spans approximately 20 million years. It includes various formations: Loncoche–Allen Formation, Jagüel Formation, Roca Formation, and Pircala–El Carrizo Formation.

The unit was discovered by Gerth in 1925, in the pathway of Loncoche, in the south of Mendoza under the term "Malargüe strata". There, this author described a sedimentary succession composed of three units: the first one is made up of limnic beds at the base and marsh at the top, the second one is merely marine, and the last one is made up of continental volcanic tuffs and conglomerates, which correspond to the Loncoche, Roca, and Pircala formations.

The Malargüe Group constitutes the upper series of the sedimentary Riográndico cycle, known originally as Malalhueyano (marine–continental), and later named Malargüe Group.

Area distribution
The Malargüe Group is covered in the eastern