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(A) Satellite map of the La Buitrera locality, with inset providing geographic context within South America. (B) Stratigraphy of the Upper Cretaceous Neuquén Group calibrated against the geologic timescale, and showing which formations yield alvarezsaurid remains. The silhouettes approximate relative size of taxa. Specific specimen and coordinate data for La Buitrera specimens are on file with the second author. Map sourced from Google Earth.

(A) Satellite map of the La Buitrera locality, with inset providing geographic context within South America. (B) Stratigraphy of the Upper Cretaceous Neuquén Group calibrated against the geologic timescale, and showing which formations yield alvarezsaurid remains. The silhouettes approximate relative size of taxa. Specific specimen and coordinate data for La Buitrera specimens are on file with the second author. Map sourced from Google Earth.

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A new coelurosaurian theropod, Alnashetri cerropoliciensis, is reported here based on articulated hind limbs of a single individual discovered at the locality of La Buitrera (Candeleros Formation, Cenomanian–Turonian), Rı´o Negro Province, Argentina. The new taxon differs from other coelurosaurs in the possession of a low ridge that separates the r...

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... Candeleros Formation, which has produced a rich fauna of both large and small dinosaurs and other vertebrates ( Leanza et al., 2004). The bulk of the known small-to medium-sized vertebrates derive from a large tract of exposures of the upper Candeleros Formation on the Río Negro shore of the Ezequiel Ramos Mexía reservoir known as La Buitrera (Fig. 1), which were discovered by the second author in ...
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... specimen was found at the ''Hoyada de los esfeno- dontes'' sublocality, part of the main fossiliferous locality of La Buitrera, about 30 km south of the village of El Chocón (Fig. 1). It was recovered from massive red sandstones that form the upper part of the Candeleros Formation, close to the contact with the Huincul Formation. However, the specimen comes from the lower levels of the outcrops in this region, where the lowermost section of the Candeleros Formation is not exposed. This unit produces a rich fauna of ...
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... distal end of the tibia is only slightly wider than the tibial shaft and does not flare broadly as in, e.g., ornithomimosaurs, oviraptorosaurs, and tyranno- sauroids. The tibia is trapezoidal and block-like in distal view, as in some enantiornithine birds and the parvicursorine taxa Shuvuuia and Mononykus, but unlike the more rostrocaudally flattened distal tibiae of most other maniraptorans (e.g., Norell & Makovicky, 1999, figure 11). The caudal surface of the distal end is marked by low medial and lateral ridges extending towards the malleolli and defining a shallow sulcus between them. ...

Citations

... A similar phylogenetic position for Linhenykus was recovered by In our tree, the clade Linhenykus þ (Ceratonykus þ Parvicursor) is sister to the clade (Mononykus þ Shuvuuia) þ (Albinykus þ Xixianykus) (Fig. 23). The grouping of Xixianykus and Albinykus was recovered also in other analyses based primarily on the TWiG data matrix (Agnolin et al. 2012;Makovicky et al. 2012;Xu et al. 2018;Lee et al. 2019;Qin et al. 2019). This clade seems to be the best-supported grouping within Parvicursorinae, having the largest GC value on our tree (Fig. 23). ...
... This clade seems to be the best-supported grouping within Parvicursorinae, having the largest GC value on our tree (Fig. 23). The clade Mononykus þ Shuvuuia is recovered in the analysis based on the second data matrix (Longrich & Currie 2009;Xu et al. 2010Xu et al. , 2011aL€ u et al. 2018) and in the analysis presented by Makovicky et al. (2012). In our tree, this clade has a low branch support (Fig. 23). ...
Article
Parvicursor remotus Karhu & Rautian, 1996 Karhu, A. A. & Rautian, A. S. 1996. A new family of Maniraptora (Dinosauria: Saurischia) from the Late Cretaceous of Mongolia. Paleontological Journal, 30, 583–592. [Google Scholar], based on a fragmentary skeleton from the Campanian Barungoyot Formation at Khulsan, in the Gobi Desert of Mongolia, is re-described in detail. Contrary to the original description, we find no evidence that the last dorsal vertebra is opisthocoelous. A biconvex last dorsal vertebra could be present in Parvicursor as in other parvicursorines. The transversely compressed sacral centrum with a sharp ventral keel is the last sacral, not the first sacral as originally alleged. The pelvic bones are not fused at the acetabulum. The holotype of P. remotus, the smallest known alvarezsaurid specimen, is a juvenile individual far from skeletal maturity. New morphological details of Parvicursor that are revealed include a ventral ridge on the posterior dorsal vertebrae; a horizontal supraacetabular crest of the ilium whose anterior end is placed anterior to the most ventrally projecting part of the pubic peduncle; the possible presence of a pubic obturator foramen; an entocondylar tuber on the femur; internal flexor flanges on metatarsals II and IV; a lateral flexor ridge on metatarsal IV; and a proximoventral notch on pedal phalanx IV-1. The Tugriken Shireh alvarezsaurid is not referable to Parvicursor because of its much larger ungual phalanx on the second pedal digit. Kol ghuva is excluded from Alzarezsauridae. The two successive sister taxa for Parvicursor are Ceratonykus and Linhenykus. Ceratonykus differs little from Parvicursor and might be a synonym of the latter. Linhenykus is very similar to Parvicursor in all overlapping skeletal elements. The Parvicursorinae includes all Asian Late Cretaceous alvarezsaurids except Qiupanykus and Nemegtonykus.
... Años más tarde, Agnolín y Novas (2011) cuestionaron su inclusión entre los dromeosáuridos. Alnashetri cerropoliciensis (Fig. 6.2), un pequeño terópodo hallado en rocas de la Formación Candeleros en la zona del Cerro Policía, constituye el más antiguo de los alvarezsáuridos registrado en Sudamérica (Makovicky et al., 2012). Gualicho shinyae Apesteguía et al., 2016 (Fig. 6.4), hallado en rocas de la Formación Huincul (Apesteguía et al., 2016a), representa el primer terópodo afín a los neovenatóridos para esta unidad geológica, un grupo estudiado también en otros lugares del mundo (e.g., Smith et al., 2008). ...
... Specimens here analysed come from different sites of La Buitrera Palaeontological Area ( Fig. 1), Río Negro Province (Northern Patagonia, Argentina), composed of five different fossil localities in a sedimentary succession of at least three intervals of the contraction and expansion of an erg-margin system, the Kokorkom desert, as the result of longterm climate changes (Candia Halupczok et al. 2018). La Buitrera Palaeontological Area has provided along two decades of collection a rich fauna of small-to medium-sized vertebrates (Apesteguía et al. 2001) including rhynchocephalians (Apesteguía & Novas 2003), limbed snakes (Apesteguía & Zaher 2006), terrestrial crocodylian (Pol & Apesteguía 2005), dromaeosaurid (Makovicky et al. 2005) and alvarezsaurid theropods (Makovicky et al. 2012), dryolestoid mammals (Rougier et al. 2011), lungfishes (Apesteguía et al. 2007), pterosaurs and turtles (Maniel et al. 2020). ...
Article
Notosuchian crocodyliforms represent an intriguing group since they are mainly terrestrial forms and therefore with completely different lifestyles than extant crocodylian, which is reflected in their particular skeletal anatomy. Although there are some inferences in the literature related to the palaeoecology of notosuchian, little is known about their biology (e.g. metabolism, growth dynamics). The palaeohistology allows us to perform interpretations about the growth dynamics and strategies of growth in these extinct forms. Here, we worked on specimens of Araripesuchus Price, 1959 (Notosuchia, Uruguaysuchidae), coming from La Buitrera Palaeontological Area, Río Negro Province (northern Patagonia, Argentina). We described for the first time the osteohistology of this taxon, based on thin sections of the stylopodium shaft (femur and humerus) of four specimens, providing an assumption of its growth dynamics. A general slow growth rate is inferred for Araripesuchus, based on the poorly vascularized parallel‐fibred/lamellar bone matrix. An unusual pattern of bone deposition was observed in two specimens; we consider this tissue as evidence of a rapid growth event at some point in the ontogeny of these individuals. Finally, it can be interpreted that in Araripesuchus, sexual maturity could be reached at least between eight to thirteen years old. This study is a first step to provide insight into the life history of these terrestrial notosuchids and to provide new empirical evidence for the osteohistological variability and palaeoecology of this peculiar group of extinct crocodyliforms.
... Of the 13 currently recognized named alvarezsaurids (based on phylogenetic placement from the most recent analyses of Qin et al., 2019, and Fowler et al., 2020, 10 derive from the Upper Cretaceous of Mongolia and China. One alvarezsaurid, Alvarezsaurus, has been recovered from Argentina, though an additional four non-alvarezsaurid alvarezsaurians (Achillesaurus; Bonepartenykus; Patagonykus; Alnashetri) are likewise known from Argentina (Bonaparte, 1991;Novas, 1997;Martinelli and Vera, 2007;Agnolin et al., 2012;Makovicky et al., 2012). Five nonalvarezsaurid alvarezsaurians are known from China, including Aorun, Haplocheirus, Xiyunykus, Tugulusaurus, and Bannykus (Choiniere et al., 2010(Choiniere et al., , 2014Xu et al., 2018). ...
Article
The Alvarezsauridae comprise a clade of small-bodied theropod dinosaurs with highly-specialized skeletal adaptations, primarily reduced but proportionately robust forelimbs which have been hypothesized as relating to an insectivorous ecology. Alvarezsaurids are known predominantly from Mongolia, China, and South America, with a comparatively sparse North American record, where alvarezsaurid remains are among the most rarely recovered vertebrate fossils from the Upper Cretaceous Western Interior. North American alvarezsaurids include Albertonykus borealis from the lower Maastrichtian Horseshoe Canyon Formation of Alberta, Canada, known from a partial skeleton and additional isolated remains, and the recently named Trierarchuncus prairiensis from the upper Maastrichtian Hell Creek Formation of eastern Montana, USA, known previously from isolated specimens, including three manual D-I unguals, a partial radius, and a partial metatarsal III. Here we describe two new manual D-I unguals referable to the alvarezsaurid Trierarchuncus from the Hell Creek Formation of eastern Montana, USA. These new unguals contribute additional detail to the currently known ontogenetic series of Trierarchuncus manual D-I unguals and indicate the sequence and degree of change that occurred through growth within these alvarezsaurid hand claws. These changes appear to be modifications and reinforcement related to stresses induced from the hypothesized ecology of alvarezsaurids as insectivores which would tear apart substrates in search of insect prey, and as such can be characterized as ecologically-driven ontogenetic changes. Additionally, we demonstrate morphological indicators for determining whether isolated alvarezsaurid manual D-I unguals pertain to the right or left manus.
... Although the knowledge of the anatomy of alvarezsaurians has been greatly improved by many recently discovered alvarezsaurid species, the internal phylogenetic relationships of Alvarezsauria remain labile (Perle et al., 1993(Perle et al., , 1994Zhou, 1995;Chiappe et al., 1996Chiappe et al., , 1997Novas, 1997;Hutchinson and Chiappe, 1998;Sereno, 2001;Suzuki et al., 2002;Martinelli and Vera, 2007;Alifanov and Barsbold, 2009;Longrich and Currie, 2009;Choiniere et al., 2010;Xu et al., 2010Xu et al., , 2011Xu et al., , 2013Nesbitt et al., 2011;Agnolin et al., 2012;Makovicky et al., 2012;Turner et al., 2012;Choiniere et al., 2010Choiniere et al., , 2013Pittman and Stiegler, 2015;Gianechini et al., 2018;Lü et al., 2018;Xu et al., 2018, Qin et al., 2019Hartmann et al., 2019). Compared to other maniraptoran lineages, alvarezsaurians occupied only the lower ranges of the body size spectrum (Fig. 1), from the~0.43 m long Parvicursor remotus (Choiniere et al., 2010;Pittman and Stiegler, 2015) to the~2.3 m long Haplocheirus sollers (Choiniere et al., 2010;Pittman and Stiegler, 2015). ...
Article
The anatomy of the alvarezsaurian tail has received relatively little attention in the paleontological literature, even though it shows a peculiar combination of anatomical characteristics that are unique among theropod dinosaurs. Nearly complete, informative tails are known from early-branching, intermediate, and late-branching taxa, allowing for robust inferences about their evolution. The alvarezsaurian tail is notable in being the longest among maniraptoran theropods, both in number of caudal vertebrae and proportional length. We examined the comparative anatomy and myology of the tail, and performed a cladistic analysis on a tail-character-based data matrix that provided a general framework for reconstructing alvarezsaurian tail evolution. Our results show that caudal vertebrae of alvarezsaurians have a combination of derived osteological features, intervertebral joint morphology, and inferred musculature, which together suggest that the tail possessed a unique function among theropods. We interpret these features as indicators of an exceptional capacity to change rotational inertia. The form and function of the tail, in combination with the fossorial forelimb, suggests that alvarezsaurians had an ecological niche similar to today's aardvark, pangolins and anteaters.
... The Candeleros Formation provided an extended list of well-known dinosaurs: among sauropods, the titanosaur Andesaurus delgadoi (Calvo and Bonaparte 1991) and some rare titanosaurs (Calvo 1999;Simón and Calvo 2002), the rebbachisauroid Nopcsaspondylus alarconensis (Apesteguía 2007), Limaysaurus tessonei (= Rebbachisaurus tessonei;Calvo and Salgado 1995;Salgado et al. 2004), and the closely related Rayososaurus agrioensis (Bonaparte 1996a). Among theropods, one of the largest worldwide predators, the giant carcharodontosaurid Giganotosaurus carolinii (Coria and Salgado 1995), the abelisaurid Ekrixinatosaurus novasi (Calvo et al. 2004), the alvarezsaurid Alnashetri cerropoliciensis (Makovicky et al. 2012), the unenlagiid Buitreraptor gonzalezorum (Makovicky et al. 2005), and the coelurosaurian Bicentenaria argentina (Novas et al. 2012a) have been found there. Ornithopod remains have been described by Coria et al. (2007). ...
Chapter
Non-mammaliaform cynodonts, formerly called “mammal-like reptiles,” illustrate earlier states of the morphological architecture in the mammalian lineage. These mammalian forerunners show unique character combinations without direct counterparts among living vertebrates reflecting adaptations long lost along the millions of years of cynodont history. The fossil record from South America, originating mostly from the Middle to Late Triassic of Argentina and Brazil, is one of the most prolific worldwide. SA non-mammalian cynodonts are systematically diverse, including approximately 40 species that present great morphological disparity in skull shape, tooth morphology, pattern of tooth replacement, masticatory mechanisms, and locomotory architectures. In this chapter, we summarize the record of SA non-mammaliaform cynodonts.
... The Candeleros Formation provided an extended list of well-known dinosaurs: among sauropods, the titanosaur Andesaurus delgadoi (Calvo and Bonaparte 1991) and some rare titanosaurs (Calvo 1999;Simón and Calvo 2002), the rebbachisauroid Nopcsaspondylus alarconensis (Apesteguía 2007), Limaysaurus tessonei (= Rebbachisaurus tessonei;Calvo and Salgado 1995;Salgado et al. 2004), and the closely related Rayososaurus agrioensis (Bonaparte 1996a). Among theropods, one of the largest worldwide predators, the giant carcharodontosaurid Giganotosaurus carolinii (Coria and Salgado 1995), the abelisaurid Ekrixinatosaurus novasi (Calvo et al. 2004), the alvarezsaurid Alnashetri cerropoliciensis (Makovicky et al. 2012), the unenlagiid Buitreraptor gonzalezorum (Makovicky et al. 2005), and the coelurosaurian Bicentenaria argentina (Novas et al. 2012a) have been found there. Ornithopod remains have been described by Coria et al. (2007). ...
Chapter
Dryolestoids are iconic members of the Mesozoic mammalian associations in South America. They achieved a large taxonomic diversity in this region with disparate dental and cranial morphotypes ranging from the classical role of sharp-toothed insectivores to bunodont, complex dentitions reflecting omnivore/herbivore adaptations. The South American radiation of dryolestoids, the meridiolestidans, are among the most abundant Cretaceous mammals, surviving the K/Pg mass extinction and continuing until the Miocene as minor members of the South American biotas. New specimens have been recently discovered, some of them including associated upper and lower jaws, and exceptionally preserved skulls. These high-quality fossils provide crucial intraspecific dental variation, both along the tooth row and from upper to lower, allowing critical re-interpretation of some taxa originally named on the basis of isolated teeth or very incomplete material. The Cretaceous diversity of meridiolestidans has been grossly overestimated, with taxa based on different dental positions of what was later determinied to be a single taxon. One relatively poorly known Late Cretaceous taxon, Groebertherium, shares many features with the classical Holartic dryolestoids and may represent a Late Jurassic/Early Cretaceous foundational morphology expected for meridiolestidans.
... The Candeleros Formation provided an extended list of well-known dinosaurs: among sauropods, the titanosaur Andesaurus delgadoi (Calvo and Bonaparte 1991) and some rare titanosaurs (Calvo 1999;Simón and Calvo 2002), the rebbachisauroid Nopcsaspondylus alarconensis (Apesteguía 2007), Limaysaurus tessonei (= Rebbachisaurus tessonei;Calvo and Salgado 1995;Salgado et al. 2004), and the closely related Rayososaurus agrioensis (Bonaparte 1996a). Among theropods, one of the largest worldwide predators, the giant carcharodontosaurid Giganotosaurus carolinii (Coria and Salgado 1995), the abelisaurid Ekrixinatosaurus novasi (Calvo et al. 2004), the alvarezsaurid Alnashetri cerropoliciensis (Makovicky et al. 2012), the unenlagiid Buitreraptor gonzalezorum (Makovicky et al. 2005), and the coelurosaurian Bicentenaria argentina (Novas et al. 2012a) have been found there. Ornithopod remains have been described by Coria et al. (2007). ...
Chapter
The sparse record of archaic Mesozoic South American mammals extends from the latest Early Jurassic to the latest Cretaceous, involving about 115 Ma, which can be further extended to about 160 Ma, including the post-K/Pg evidence. We review here the distribution, predicted time of origin, and likely place of origin for the lineages covered in the preceding chapters during that span of time and against the evolving geological backdrop of continental drift and paleogeography. Size, dental diversity, and likely dietary specializations of the Mesozoic South American mammals are discussed in the context of Mesozoic mammals in general. A few of the many surprising advances in comparative genetic and molecular evolution are discussed as part of a holistic view of early mammalian evolution to which fossils can, and should, be integrated. Social, financial, and geographical issues affecting paleontological research in South America, early mammals, in particular, are highlighted. We recognize that we are still in the early stages of development and that much of what we know about Mesozoic South American mammals is likely to be drastically altered by finds in the continent or underrepresented areas from formely Gondwanan landmasses such as Antarctica or Africa. Their scarce mammalian fossil record has hampered their full incorporation into an integrated view of early mammalian evolution. The relatively robust paleontological community present in several South American countries, relatively inexpensive nature of the discipline, and extensive outcrops are likely to ensure continuity of a synergistic research agenda. The potential for novel data, regional strengths in systematics, and the global resurgent importance of time as integral to model-based phylogenies are auspicious signs for the future of Mesozoic mammal research in South America.
... Fossil discoveries within the past three decades have revealed an unexpected diversity of tetanuran theropod dinosaurs from Cretaceous localities in the Southern Hemisphere landmasses, especially South America (e.g., Bonaparte 1991;Coria and Salgado 1995;Kellner and Campos 1996;Martill et al. 1996;Novas 1997Novas , 1998Novas and Puerta 1997;Kellner 1999;Naish et al. 2004;Makovicky et al. 2005Makovicky et al. , 2012Novas and Pol 2005;Novas et al. 2005Novas et al. , 2008aNovas et al. , 2008bNovas et al. , 2012Coria andCurrie 2006, 2016;Martínez and Novas 2006;Martinelli and Vera 2007;Sereno et al. 2008;Kellner et al. 2011;Porfiri et al. 2011aPorfiri et al. , 2018Agnolín et al. 2012;Apesteguía et al. 2016;Motta et al. 2016Motta et al. , 2020Coria et al. 2020; see reviews in Novas et al. 2013;Ezcurra and Novas 2016). Among the most enigmatic of these predominantly Gondwanan tetanuran clades is Megaraptora, definitively represented in South America by the Argentinean Late Cretaceous species Aerosteon riocoloradensis (Sereno et al. 2008), Megaraptor namunhuaiquii (Novas 1998;Calvo et al. 2004;Porfiri et al. 2007aPorfiri et al. , 2007bPorfiri et al. , 2008Porfiri et al. , 2014Paulina-Carabajal and Porfiri 2018), Murusraptor barrosaensis (Coria and Currie 2016;Paulina-Carabajal and Currie 2017;Aranciaga Rolando et al. 2019), Orkoraptor burkei (Novas et al. 2008a), and Tratayenia rosalesi , as well as multiple taxonomically indeterminate (e.g., Aranciaga Rolando et al. 2015Novas et al. 2019;Ibiricu et al. 2020) or as-yet undescribed (e.g., Porfiri et al. 2011b;Casal et al. 2019;Méndez et al. 2019) specimens. ...
Article
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We describe two partial postcranial skeletons belonging to the enigmatic theropod dinosaur clade Megaraptoridae from the Upper Cretaceous (lower Cenomanian-upper Turonian) Bajo Barreal Formation of southern Chubut Province, central Patagonia, Argentina. The specimens are assigned to Megaraptoridae due to their possession of multiple anatomical features that are considered synapomorphies of that predatory dinosaur group, such as a greatly enlarged, laterally compressed ungual of manual digit I that possesses asymmetrical lateral and medial vascular grooves. Overlapping elements of the two skeletons are nearly identical in morphology, suggesting that they probably represent the same taxon, a large-bodied theropod that was previously unknown from the early Late Cretaceous of southern South America. The Bajo Barreal specimens constitute the most ancient unquestionable records of Megaraptoridae from that continent, and exhibit particularly strong osteological resemblances to penecontemporaneous megaraptorids from the Winton Formation of Australia. Phylogenetic analysis recovers the unnamed Bajo Barreal taxon as the earliest-diverging South American megaraptorid and the oldest-known representative of this clade that likely attained a body length of at least seven meters and a mass of at least one metric ton. Overall, the balance of the evidence suggests that megaraptorids originated in eastern Gondwana (Australia) during the Early Cretaceous, then subsequently dispersed to western Gondwana (South America) during the mid-Cretaceous, where they attained substantially larger body sizes, ultimately coming to occupy the apex predator niches in their respective habitats.
... As for the prolific paleontological record of the Candeleros Formation in the LBPA, the unit is wellknown for the variety of its vertebrate findings. These include a rich fauna in tetrapods, (Apesteguía, 2001), rhynchocephalian lepidosaurs, limbed snakes (Garberoglio et al., 2019), uruguaysuchid crocodyliforms (Pol and Apesteguía, 2005), a dromaeosaurid (Makovicky et al., 2005), an alvarezsaurid (Makovicky et al., 2012), theropod dinosaurs, fragmentary sauropods, dryolestoid mammals (Rougier et al., 2011), ceratodontiform dipnoans (Apesteguía et al., 2007) and more recently a new species of turtle (Maniel et al., 2020). Moreover, specifically in the studied location, dinosaur tracks have been recognized in the aeolian sandstones (Candia Halupczok et al., 2018). ...
Article
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Several studies have emphasized the complexity of the interaction between fluvial and aeolian processes at erg margin settings, and their importance in the resulting geological record. The Cretaceous Candeleros Formation in the "Cañadón de Las Tortugas" site which is located in "La Buitrera Paleontological Area" (Neuquén Basin, Argentina) provides excellent outcrops where the record of a variety of interactions between the aeolian and fluvial processes can be observed. Therefore, the aim of this project was to reconstruct the accumulation systems and the spatial and temporal relations of their associated sedimentary processes. The methodology included the logging of sedimentary sections, a facies and architectural analysis and the identification of the different hierarchies of unconformities. The different architectural elements identified are related both to aeolian and fluvial genesis as mentioned before. The first ones comprise aeolian dune deposits and wet interdune deposits, whilst the second ones are channelized deposits, non-channelized proximal fluvial deposits and non-channelized distal fluvial deposits. These architectural elements were identified in three different evolutive stages of the depositional model made. Hence, the studied interval has a complex pile of overlapping units that represents the contraction/expansion of an erg-margin system as a result of variations of the water table position to climatic conditions. Therefore, this study enhances current understanding of the stratigraphic record of erg margin systems at different time-space scales. This high-resolution study provides a detailed account of the processes that operated in the Kokorkom paleodesert and relevant information for the reconstruction of the accumulation systems in the southern part of the Neuquén Basin during the Late Cretaceous.