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The sauropod record of Salitral Ojo del Agua: An Upper Cretaceous (Allen Formation) fossiliferous locality from northern Patagonia, Argentina

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Abstract

The record of sauropods in the Upper Cretaceous of Patagonia is rich. However, there are still several blanks on this record. Here it is described a new sauropod assemblage coming from the Salitral Ojo de Agua Area, Río Negro province, northern Patagonia, Argentina (Allen Formation; Maastrichtian). Remains of indeterminate saltasaurines, aeolosaurines, as well as new specimens of the small saltasaurine Rocasaurus muniozi and the new eutitanosaur Menucocelsior arriagadai gen. et sp. nov., are described.. The new eutitanosaur is represented by an incomplete caudal series and some appendicular bones that indicate that it does not belong to any previously recognized eutitanosaur clade (e.g, Colossosauria, Saltasaurinae, Aeolosaurini). The co-occurrence of several roughly coeval titanosaurs in a restricted area (as occur in Bajo de Santa Rosa, Salitral Moreno and Salitral Ojo de Agua sites) with different body plans, indicates that they probably occupied particular ecological niches and that probably competition for resources was limited, allowing the connivance of several taxa in a single locality and age. This pattern is not observed in other sites of the world. Based on these records and on the high diversity of osteoderm morphotypes recovered, it appears to be certain that palaeoecological conditions in the area were able to sustain and promote the flourishing of many species of titanosaurs.

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... Alternative hypotheses concerning the small size of South American ankylosaurs (and within the struthiosaurines) include competitive exclusion against hadrosaurids and the endemic diversity of Late Cretaceous sauropods (Salgado & Azpilicueta 2000), which includes small-sized forms (de Jesus Faria et al. 2014;Aranciaga-Rolando et al. 2021, and references therein). Paedomorphic dwarfism has also been discussed previously (Pereda-Suberbiola & Galton 2009). ...
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SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP; CT data are available as Morphobank project P2093 at http://www.morphobank.org.
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The neck posture and function in sauropods have been widely studied during the last decades. The cartilaginous neutral pose (CNP) method is commonly used in biomechanical reconstructions by positioning the vertebrae with the joint surfaces aligned to obtain the ‘neutral pose’. However, few studies have analysed the posture and function of the tail of sauropods. The published data suggest that most sauropods maintained their tails in a horizontal position. We test the neutral pose hypothesis in the anterior caudal vertebrae (C4 to C9) of Aeolosaurus maximus (Titanosauria, Sauropoda), a member of Aeolosaurini endemic of South America, by using the following methodologies: CNP, and range of movement (RoM). The results show that the tail of A. maximus possibly presented in a sigmoidal format which differs from the horizontal position commonly inferred to other sauropods. A. maximus is the first sauropod with caudal vertebrae presenting in situ protonic posture, which corroborates the neutral pose hypothesis and demonstrates that this characteristic is possibly a feature of the Aeolosaurini clade.
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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.
Article
A new Late Cretaceous titanosaurian sauropod from the Sierra Barrosa locality (Anacleto Formation, Late Cretaceous, early Campanian) of Neuquén Province, Argentina, Barrosasaurus casamiquelai gen. et sp. nov., is described. The holotype of this species consists of three large and incomplete, although well-preserved, dorsal vertebrae (one probably the third, the next the seventh or eighth, and the last the ninth or tenth). The arrangement of neural arch laminae in the dorsal vertebrae of this titanosaur differs from that present in other genera in the following ways: the spinoprezygapophyseal laminae are well developed in the third vertebra, and relictual in the seventh or eighth vertebra; two spinodiapophyseal laminae are present in the seventh or eighth and in the ninth or tenth vertebrae, the anterior spinodiapophyseal lamina being more strongly developed than the posterior spinodiapophyseal lamina in the ninth or tenth vertebra. These characters, among others, allow the recognition of this individual as a new species of Titanosauria, which increases knowledge of the diversity of titanosaurs in the Late Cretaceous of Patagonia.
Article
The paleobiogeographic significance of continental Africa during the middle and Late Cretaceous is not well understood, in part due to incomplete sampling from large portions of the landmass during these intervals. Intensified field efforts in the Galula Formation exposed in southwestern Tanzania have revealed a diverse vertebrate fauna, including the novel titanosaurian Shingopana songwensis, gen. et sp. nov., described herein. Based on a left angular, cervical vertebrae, cervical and dorsal ribs, a left humerus, and a partial left pubis, Shingopana exhibits morphology indicating affinities with the Late Cretaceous aeolosaurine titanosaurians of South America. The bulbous expansion of the cervical vertebral neural spine is similar to the condition in Bonitasaura salgadoi, Overosaurus paradasorum, and Trigonosaurus pricei. The dorsal ribs of Shingopana also present proximal anterior and posterior flanges that previously were proposed to be unique to Overosaurus. Furthermore, Shingopana is diagnosed by a divided spinoprezygapophyseal lamina in the middle-to-posterior cervical vertebrae. Parsimony and both uncalibrated and tip-dated Bayesian phylogenetic approaches support Shingopana as the first African titanosaurian that is closely related to aeolosaurines. Comparisons with other African titanosaurians, such as the co-occurring Rukwatitan bisepultus and geographically proximate Malawisaurus dixeyi, suggest that southern African forms represent diverse taxa rather than forming a monophyletic group. Moreover, southern African forms exhibit stronger affinities with South American clades than with representative northern African form, suggesting that tectonically driven separation of the two landmasses may have influenced the development of progressively isolated southern African faunas throughout the Cretaceous. http://zoobank.org/urn:lsid:zoobank.org:pub:9F7B574F-C27C-4753-AFB6-51A053A05BC4 http://morphobank.org/permalink/?P2662 SUPPLEMENTAL DATA—Supplemental materials are available for this article for free at www.tandfonline.com/UJVP Citation for this article: Gorscak, E., P. M. O'Connor, E. M. Roberts, and N. J. Stevens. 2017. The second titanosaurian (Dinosauria: Sauropoda) from the middle Cretaceous Galula Formation, southwestern Tanzania, with remarks on African titanosaurian diversity. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2017.1343250.
Article
Saltasaurine titanosaurs are characterized by their relatively small size compared to other sauropods, extreme postcranial pneumaticity, and dermal armour covering the body. This group has been reported in the Upper Cretaceous of the Lecho, Allen, and Anacleto formations of Argentina. We describe here a new saltasaurine specimen (MACN-Pv RN 233) from the Campanian of the Angostura Colorada Formation (Río Negro Province) that is represented by eight caudal vertebrae and six osteoderms. This specimen is described in detail and its phylogenetic relationships with the other three known saltasaurines, as well as its implications to the knowledge of caudal vertebra and osteoderm anatomy, are discussed. Our results place MACN-Pv RN 233 more closely related to Saltasaurus loricatus and Rocasaurus muniozi than to Neuquensaurus australis. MACN-Pv RN 233 possesses a combination of features that differ from other saltasaurines, but because of the fragmentary nature of the specimen we decided for the sake of taxonomic stability to not erect a new taxon. This specimen shows the first unambiguous evidence of chevron pneumatisation for a sauropodomorph, implying a broader osteological invasion of the diver-ticula from the abdominal air sac than previously thought for this group of dinosaurs. MACN-Pv RN 233 preserves two osteoderm morphotypes, one similar to those reported for Neuquensaurus australis and Saltasaurus loricatus. This new specimen expands the distribution of the group to a new geological unit and increases the dinosaur diversity known for the Angostura Colorada Formation.
Article
Remains assigned to Aeolosaurus Powell, 1986 from the Allen Formation are described. The specimen differs from the holotype of Aeolosaurus rionegrinus Powell, 1986 in the length of the prezigapophyses, relative position of the postzigapophyses, and radius and ischium morphology. Considerations on a specimen tentatively assigned to the type species, and modified diagnosis of genus are included. Association of dermal plates to the specimen here described is commented. -English summary
Article
A new saltasaurine taxon based on a femur, pelvic bones and dorsal and caudal vertebrae is described. The closest relationships of the new taxon are with Saltasaurus loricatus Bonaparte and Powell from northwestern Argentina. These species share caudal vertebrae bearing a ventral depression divided by a longitudinal septum. The record of Saltasaurinae is thus limited to the Upper Cretaceous of Argentina, with three distinct taxa: Saltasaurus loricatus, Neuquensaurus australis Lyddeker and Rocasaurus muniozi n. gen., n. sp.
Article
Several bony plates referred to titanosaurs are reviewed. Two groups of plates, exhumated from two different localities, LagoPellegrini-Cinco Saltos and Salitral Moreno, in the province of Río Negro, are described. Several characters diferenciate the two groups, as the presence in one group of a shallow dorsal depression (Type I sensu Huene), a dorsal awn, a ventral ridge, and a cingulum. Generally, most of the plates are symmetrical, although a few present a marked asymmetry. The former apparently were located in the midline of the body over the neural spines, and the others laterally on both sides of the animal body. Histologically, the plates are composed ventrally by cancellous bone and externally by Haversian bone, and the Sharpey's fibers are present, mainly, in the periphery on the dorsal surface of the plates.
Article
The holotype of Pellegrinisaurus powelli nov. gen. et sp., recovered from levels of Alien Formation at lago Pellegrini (Province of Río Negro, Argentina) is described. Previous reference of this specimen to c. Epachthosaurus sp. is discarded, as it does not share derived features with the holotype of Epachthosaurus sciuttoi Powell. Probable autapomorphies of Pellegrinisaurus powelli are: (1) transverse width of the centrum of the posterior dorsal vertebrae approximately twice the maximum dorsoventral depth, and (2) mid-posterior and posterior caudal vertebrae with anteroposteriorly elongated and dorsoventrally depressed neural spines, the anterior ends of which are higher anteriorly than posteriorly. Pellegrinisaurus powelli is considered a probable sister taxon of the Saltasaurinae on account of low vertebral centra in the medial and posterior caudals, with dorso-ventrally convex lateral faces.
Article
We present new remains from the Campanian-Maastrichtian beds of the Allen Formation, in Salitral Ojo de Agua (Río Negro, Argentina), which are assignable to Alvarezsauridae indet. This clade of small coelurosaurian theropods is known from strata of similar age in Mongolia, and from older sediments (Turonian and Coniacian in age) in Argentina. Thus, the material presented here extends the temporal record of the alvarezsaurids from the Southern Hemisphere up to the Latest Cretaceous. The fossil bones reported were associated to eggshells of the oofamily Elongatoolithidae, which are actually attributed to Theropoda.
Chapter
The description of mass extinctions, one of the unique gifts of palaeontology to evolutionary and ecological theory, is a rich source of opportunities for generating and testing hypotheses about the regulation of speciation, faunal diversification, and the fate of clades. The two best-known mass extinctions are those at the Permian–Triassic boundary and at the Cretaceous–Tertiary boundary. For terrestrial vertebrates, the most discussed extinctions are those at the end of the Pleistocene and at the Cretaceous–Tertiary boundary. Most proposed explanations are ad hoc—search is made for a climatic or other environmental change during the extinction event, and when evidence for such change is found, the change itself is indicted as the agent, which directly or indirectly caused the extinctions. Community composition patterns are thus drawn for the Early Permian of North America, the Late Permian and Triassic of South Africa, and the Early Cretaceous and Late Jurassic of North America.
Article
The dinosaur record of the Salitral Moreno locality (Rio Negro Province, Argentina) is characterized by a high diversity of herbivore taxa, among them hadrosaurs, ankylosaurs, and titanosaur sauropods, but carnivores are rare, consisting of only a few fragmentary bones of small forms. Titanosaurs are represented by Rocasaurus muniozi and Aeolosaurus sp., and at least four other taxa, represented by fragmentary material. The elements preserved include a cervical, dorsal and caudal vertebrae, chevron, humerii, ulnae, radii, metacarpal, femora, tibiae, metatarsal, ischia, pubis, and ilium. The Allen Formation is thought to be correlated with the Marilia Formation in Brazil, and their faunas have certain elements in common such as aeolosaurines, but saltasaurines and hadrosaurs, are known exclusively from the Allen Formation. These absences, and particularly that of the saltasaurines, may be because those sauropods originated late in the Cretaceous, probably in southern South America (Northern Patagonia?), and they did not have time to disperse to northern South America.
Article
Titanosaurs are the only group of sauropodomorph dinosaurs that possesses osteoderms. The Anacleto and Allen formations (Upper Cretaceous) from northern Patagonia (Argentina) have provided an abundance of these elements, isolated or associated with more or less complete skeletons. Here, we study the morphology, microanatomy, and histology of titanosaur osteoderms found in these stratigraphic units. The size and gross anatomy of the osteoderms are strongly variable, as well as their microanatomy, which ranges from compact structures to those with strong development of cancellous bone. The primary bone tissue is composed of structural fiber bundles that are ossified by dermal metaplasia. Bone pathologies were identified in at least two osteoderms. Bone histology suggests that the osteoderms were entirely imbedded in the stratum compactum of the dermis. Titanosaur osteoderms were probably employed for multiple functions, including mineral storage and defense.
Article
Titanosauriformes was a globally distributed, long-lived clade of dinosaurs that contains both the largest and smallest known sauropods. These common and diverse megaherbivores evolved a suite of cranial and locomotory specializations perhaps related to their near-ubiquity in Mesozoic ecosystems. In an effort to understand the phylogenetic relationships of their early (Late Jurassic–Early Cretaceous) members, this paper presents a lower-level cladistic analysis of basal titanosauriforms in which 25 ingroup and three outgroup taxa were scored for 119 characters. Analysis of these characters resulted in the recovery of three main clades: Brachiosauridae, a cosmopolitan mix of Late Jurassic and Early Cretaceous sauropods, Euhelopodidae, a clade of mid-Cretaceous East Asian sauropods, and Titanosauria, a large Cretaceous clade made up of mostly Gondwanan genera. Several putative brachiosaurids were instead found to represent non-titanosauriforms or more derived taxa, and no support for a Laurasia-wide clade of titanosauriforms was found. This analysis establishes robust synapomorphies for many titanosauriform subclades. A re-evaluation of the phylogenetic affinities of fragmentary taxa based on these synapomorphies found no body fossil evidence for titanosaurs before the middle Cretaceous (Aptian), in contrast to previous reports of Middle and Late Jurassic forms. Purported titanosaur track-ways from the Middle Jurassic either indicate a substantial ghost lineage for the group or – more likely – represent non-titanosaurs. Titanosauriform palaeobiogeographical history is the result of several factors including differential extinction and dispersal. This study provides a foundation for future study of basal titanosauriform phylogeny and the origins of Titanosauria. © 2012 The Linnean Society of London, Zoological Journal of the Linnean Society, 2012, 166, 624–671.