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is a basal titanosaur from the early Late Cretaceous of central Patagonia, Argentina. Here, we present the reconstruction of the pelvic and hindlimb musculature of this titanosaur, based on the soft tissue data of extant archosaurs. The majority of the pelvic, hindlimb and pes muscles are within a decisive and positive level of inference. Comparison with a derived titanosaur such as Neuquensaurus, shows several morphological differences which are directly related with the muscular attachments, supporting differences about the musculature arrangement between these two sauropod dinosaurs. For example, the anterior projection of the preacetabular process of Neuquensaurus extends more laterally, whereas in Epachthosaurus the preacetabular process is laterally less extended. The fibular lateral tuberosity in Neuquensaurus is closer to the fibular head than it is in Epachthosaurus. The femoral fourth trochanter in Neuquensaurus is closer to the femoral head than it is in Epachthosaurus. Likewise, the caudofemoralis longus may have extended more distally in the tail in Epachthosaurus.These differences, among others, may have influenced the muscular arrangement and, therefore, the locomotor function abilities of these titanosaurs. Finally, this myological description of Epachthosaurus, where twenty one muscles were reconstructed, constitutes useful data for researches interested in functional anatomy. [ABSTRACT FROM AUTHOR]

In dinosaurs and other archosaurs, the presence of foramina connected with internal chambers in axial and appendicular bones is regarded as a robust indicator of postcranial skeletal pneumaticity (PSP). Here we analyze PSP and its paleobiological implications in rebbachisaurid diplodocoid sauropod dinosaurs based primarily on the dorsal vertebrae of Katepensaurus goicoecheai, a rebbachisaurid from the Cenomanian-Turonian (Upper Cretaceous) Bajo Barreal Formation of Patagonia, Argentina. We document a complex of interconnected pneumatic foramina and internal chambers within the dorsal vertebral transverse processes of Katepensaurus. Collectively, these structures constitute a form of PSP that has not previously been observed in sauropods, though it is closely comparable to morphologies seen in selected birds and non-avian theropods. Parts of the skeletons of Katepensaurus and other rebbachisaurid taxa such as Amazonsaurus maranhensis and Tataouinea hannibalis exhibit an elevated degree of pneumaticity relative to the conditions in many other sauropods. We interpret this extensive PSP as an adaptation for lowering the density of the skeleton, and tentatively propose that this reduced skeletal density may also have decreased the muscle energy required to move the body and the heat generated in so doing. Given that several rebbachisaurids inhabited tropical to subtropical paleolatitudes during the extreme warmth of the mid-Cretaceous, increased PSP may have better enabled these sauropods to cope with extraordinarily high temperatures. Extensive skeletal pneumaticity may have been an important innovation in Rebbachisauridae, and perhaps also in saltasaurine titanosaurs, which evolved an even greater degree of PSP. This may in turn have contributed to the evolutionary success of rebbachisaurids, which were the only diplodocoids to survive into the Late Cretaceous. [ABSTRACT FROM AUTHOR]

Here we report multiple lamniform shark teeth recovered from fluvial sediments in the (Campanian-Maastrichtian) Cerro Fortaleza Formation, Santa Cruz Province, Argentina. This small tooth assemblage is compared to various lamniform sharks possessing similar dental morphologies, including Archaeolamna, Cretalamna, Dwardius, Dallasiella, and Cretodus. Although the teeth share numerous morphological features with the genus Archaeolamna, including a developed neck that maintains a relatively consistent width along the base of the crown, the small sample size and incomplete nature of these specimens precludes definitive taxonomic assignment. Regardless, the discovery of selachian teeth unique from those previously described for the region broadens the known diversity of Late Cretaceous South American sharks. Additionally, the discovery of the teeth in fluvial sandstone may indicate a euryhaline paleobiology in the lamniform taxon or taxa represented by this tooth assemblage. [ABSTRACT FROM AUTHOR]

Due to their abundance, taxonomic and morphological diversity, wide range of body sizes and broad geographical distribution, titanosaurian sauropods were one of the most important Cretaceous herbivorous dinosaur groups. Consequently, titanosaurs constitute one of the best samples in which to evaluate the relationship between bony structures and unpreserved soft-tissues within Sauropoda. We reconstruct the morphology and interpret the implications of selected soft-tissues associated with the titanosaurian caudal skeleton. These tissues, especially the M. caudofemoralis longus (CFL), exerted a considerable influence on the anatomy of the caudal vertebrae and haemal arches. In all studied titanosaurian taxa, the reconstructed caudofemoral musculature corresponds to one of three principal morphotypes that accord with previously recognised phylogenetic patterns within the clade. Basal titanosaurians had an elongate M. CFL that extended for much of the proximal half of the tail; in saltasaurines, this muscle was much shorter. Non-saltasaurine lithostrotians exhibited an intermediate condition. Furthermore, the differing position of the fourth trochanter, and therefore, the insertion of the caudofemoral muscles, among various titanosaurian taxa suggests distinctions in the locomotor function of these animals. [ABSTRACT FROM AUTHOR]

Background: Central Patagonia, Argentina, preserves an abundant and rich fossil record. Among vertebrate fossils from the Upper Cretaceous Bajo Barreal Formation of Patagonia, five individuals of the small, non-avian theropod dinosaur Aniksosaurus darwini were recovered. Group behavior is an important aspect of dinosaur paleoecology, but it is not well-documented and is poorly understood among non-avian Theropoda. Methods/Principal Findings: The taphonomic association of individuals from the Bajo Barreal Formation and aspects of their bone histology suggest gregarious behavior for Aniksosaurus, during at least a portion of the life history of this species. Histology indicates that the specimens were juvenile to sub-adult individuals. In addition, morphological differences between individuals, particularly proportions of the appendicular bones, are probably related to body-size dimorphism rather than ontogenetic stage. Conclusions/Significance: Gregarious behaviour may have conferred a selective advantage on Aniksosaurus individuals, contributing to their successful exploitation of the Cretaceous paleoenvironment preserved in the Bajo Barreal Formation. The monospecific assemblage of Aniksosaurus specimens constitutes only the second body fossil association of small, coelurosaurian theropods in South America and adds valuable information about the paleoecologies of non-avian theropod dinosaurs, particularly in the early Late Cretaceous of Patagonia. [ABSTRACT FROM AUTHOR]

We describe and incorporate fragmentary new cranial and postcranial materials of hadrosaurid ornithopods into the non-avian dinosaur assemblage of the Upper Cretaceous (Coniacian–Maastrichtian) Lago Colhué Huapi Formation of central Patagonia, south-central Chubut Province, Argentina. The fossils come from the upper part of the formation, probably from a stratigraphic interval close to the Cretaceous/Paleogene boundary. The materials belong to at least two ontogenetically distinct individuals that are assigned to Hadrosauridae due to their possession of anatomical features that characterize this derived ornithopod group. Sedimentological inferences reveal that the paleoenvironment of these hadrosaurids was characterized by high-sinuosity, meandering-type fluvial channels, whereas palynological data suggest the existence of low-energy freshwater bodies in the floodplains of these rivers and a warm and humid paleoclimate. The deposition of the upper part of the Lago Colhué Huapi Formation was probably influenced by the Patagonian Atlantic marine transgression, which may have played an important role in the distribution of this sedimentary unit. The new Lago Colhué Huapi Formation hadrosaurid specimens constitute the most stratigraphically recent records of this clade from Argentina. The materials contribute to the interpretation of Upper Cretaceous hadrosaurid paleobiogeography in Patagonian basins; moreover, sedimentological and palynological data suggest that paleoenvironmental conditions may have exerted an important influence on South American hadrosaur distribution, supporting hypotheses of ornithopod faunal turnover during the Late Cretaceous of central Patagonia. Finally, the new remains add to the generally depauperate record of Late Cretaceous ornithopods in the Southern Hemisphere. • New remains hadrosaurid ornithopods from the Latest Cretaceous of the Lago Colhué Huapi Formation (Chubut Group, Golfo San Jorge Basin) are reported. • The distribution of Late Cretaceous ornithopods in southern South America was directly related to paleoenvironmental conditions. • The proximity of the paleoshoreline, could have favored hadrosaurids over earlier-diverging ornithopods such as elasmarians. • The Atlantic marine transgression may have played an important role in the distribution of hadrosaurids. [ABSTRACT FROM AUTHOR]

In this paper, we present an updated revision of fossil vertebrates from the Chubut Group, Golfo San Jorge Basin, while also describing some new remains. Extensive exposures of both Lower and Upper Cretaceous sedimentary sequences are present in central Patagonia. These outcrops have, over the past several decades, yielded a varied vertebrate fauna, including fishes, turtles, crocodyliforms, pterosaurs, and dinosaurs, currently herein characterized and described. Although vertebrate diversity in the Chubut Group in central Patagonia is remarkable, the most abundant vertebrates recovered are dinosaurs. The Matasiete Formation (Hauterivian?–Albian) is markedly less prolific in terms of fossils discoveries than either the Bajo Barreal Formation (Cenomanian–early Turonian) or the recently recognized Lago Colhué Huapi Formation (Coniacian–Maastrichtian). The Bajo Barreal fauna is, at a high level, typical of coeval Gondwanan faunas. However, interestingly, several taxa occupy a basal position within their respective groups. The Lago Colhué Huapi Formation has produced a more derived vertebrate fauna, again similar to those from other Gondwanan regions. Finally, in a broad context, the new materials described augment our understanding of Cretaceous terrestrial vertebrate assemblage of central Patagonia and add to the generally meager record of vertebrate in the Cretaceous of the Southern Hemisphere. • South-central Patagonia preserves a rich and important vertebrate fossil record. • New materials described augment our understanding of Cretaceous vertebrate. • The information mentioned constitutes an important source for future comparisons. [ABSTRACT FROM AUTHOR]

We present the first integrate paleoecological study which includes both previous and new sedimentological, paleoclimate, fauna and flora analyses in the Bajo Barreal Formation (Upper Cretaceous), Golfo San Jorge Basin, Patagonia, Argentina. The study was carried out principally at the Estancia (=Ranch) Ocho Hermanos Locality, although other significant paleontological localities of the Bajo Barreal Formation are included. In the Estancia Ocho Hermanos Locality, the paleoenvironment is characterized by low sinuosity single-channelized fluvial systems, with well-developed proximal floodplains. Paleoclimate was interpreted as warm and humid with marked seasonality. This locality was dominated by dinosaurs, including sauropods (titanosaurs and rebbachisaurids) and theropods (abelisaurids and megaraptorids), but other vertebrates, such as pterosaurs, crocodyliforms, turtles and fishes were also part of the paleoecosystem. In addition, the first stable isotope analysis on Mesozoic teeth (dinosaurs and crocodyliforms) from the Golfo San Jorge Basin was conducted. This new information revealed different sources of water utilized by theropod and sauropod dinosaurs, allowed to infer preliminary modes of life for crocodyliforms, and provided information about diet of these Mesozoic organisms. Ground-level and mid-height feeding are interpreted for rebbachisaurid and titanosaurid sauropods, respectively. Ferns are considered the main non-arboreal component of this ecosystem and possibly an important source of the diet of sauropods, whereas angiosperms (eudicots and monocots) would have been present as well. On the other hand, gymnosperms, mainly Araucariaceae, and in a minor proportion Podocarpaceae, and Cheirolepidiaceae, would encompass the arboreal component of this environment. Abelisaurids could be recognized as one of the top predators of this paleoecosystem, in part due to their relative abundance, in relation to other carnivores. Finally, in a broad context, this study augments our understanding of Cretaceous terrestrial ecosystems of south-central Patagonia and contributes for future comparisons with other chronologically equivalent localities, principally, from the Southern Hemisphere. • A reconstruction of the paleoecosystem of the Bajo Barreal Formation is proposed. • The paleoecosystem is dominated by dinosaurs, but other vertebrates are present. • Different height feeding levels are interpreted for titanosaurs and rebbachisaurids. • The paleoclimate is interpreted as warm and humid with marked seasonality. • First stable isotope analysis is conducted on fossils of the Golfo San Jorge Basin. [ABSTRACT FROM AUTHOR]

In the last two decades, the number of phylogenetically informative anatomical characters recognized in the appendicular skeleton of titanosaurian sauropod dinosaurs has increased dramatically with the discovery of new and comparatively complete specimens. Here we provide an overview of the appendicular skeletal morphology of South American titanosaurs and discuss its significance for phylogenetic reconstruction. The appendicular skeletal diversity of South American titanosaurs is substantially greater than was initially appreciated. Moreover, some regions of the appendicular skeleton, such as the pes, exhibit remarkable variability in form. Multiple synapomorphies of Titanosauria and the less inclusive clades Lithostrotia and Saltasauridae consist of characters of the girdles and limbs. Although the phylogenetic definitions of titanosaurian clades such as Saltasaurinae and Lognkosauria are stable, the taxonomic content of these clades has varied in recent analyses depending on the phylogenetic topology recovered. Within Titanosauria, the results of four recent, largely independent analyses support the existence of a derived titanosaurian lineage distinct from the 'Saltasaurinae line,' which is herein termed Colossosauria. At present, this clade is mainly comprised by taxa within Lognkosauria and Rinconsauria, and is useful in discussions of titanosaurian lower-level relationships.

Supraspinous ossified rods have been reported in the sacra of some derived sauropod dinosaurs. Although different hypotheses have been proposed to explain the origin of this structure, histological evidence has never been provided to support or reject any of them. In order to establish its origin, we analyse and characterize the microstructure of the supraspinous rod of two sauropod dinosaurs from the Upper Cretaceous of Argentina. The supraspinous ossified rod is almost entirely formed by dense Haversian bone. Remains of primary bone consist entirely of an avascular tissue composed of two types of fibre-like structures, which are coarse and longitudinally (parallel to the main axis of the element) oriented. These structures are differentiated on the basis of their optical properties under polarized light. Very thin fibrous strands are also observed in some regions. These small fibres are all oriented parallel to one another but perpendicular to the element main axis. Histological features of the primary bone tissue indicate that the sacral supraspinous rod corresponds to an ossified supraspinous ligament. The formation of this structure appears to have been a non-pathological metaplastic ossification, possibly induced by the continuous tensile forces applied to the element.

The Bajo Barreal Formation (Cenomanian, Late Cretaceous; central Patagonia, Argentina) preserves an important and rich fossil record. Among the dinosaurs described, a small ornithischian, Notohypsilophon comodorensis, was named in the 1990s. This small-bodied dinosaur, the most complete representative of the group discovered in that formation, was described as a "hypsilophodontid" ornithopod based on close morphological affinities with other members of that group, which is currently regarded as paraphyletic. Within this context, we present a restudy of Notohypsilophodon. This dinosaur is considered a basal ornithopod, probably more basal than Gasparinisaura. Likewise, this analysis emends and provides additional unique anatomical characters that support its taxonomic validity and position. On the basis of weak evidence, Notohypsilophodon might share the presence of gastroliths with other basal ornithopods (Gasparinisaura and Haya), which could suggest a specific behavior in response to its food ingestion. Finally, this study increases our knowledge of the evolutionary dynamics of South American Cretaceous ornithopods, and therefore broadens our knowledge of the early Late Cretaceous continental vertebrate assemblages of central Patagonia and of the Southern Hemisphere in general.