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Last Titans: Titanosaurs From the Campanian–Maastrichtian Age
Abstract
After the extinction of rebbachisaurids during the Cenomanian–Turonian interval, titanosaurs were the only group of sauropods to face the K–Pg event. This same global pattern also holds for the end-Cretaceous (Campanian–Maastrichtian) titanosaur record in South America, where their remains can be found from southern Argentina to Ecuador, with more frequent findings in Argentina and Brazil. In this chapter, we review these fossil findings and the main aspects of the taxonomy, systematics, and paleogeographic implications of this record and briefly discuss the importance of these occurrences for the understanding of titanosaur evolution. The diversity and abundance of end-Cretaceous titanosaur taxa in South America represent about 25% of the known Titanosauria species in the world, which makes them the most common group of large terrestrial herbivores of that time. Cretaceous titanosaurs from South America also vary highly in morphology and size, comprising small to large-sized taxa, for example. Their record mainly consists of appendicular and axial remains, including rare skull material, but also comprises eggs, nests, footprints, and coprolites. In South America, by the end of the Late Cretaceous, titanosaurs were generally represented by more derived titanosaurians that are mainly taxonomically assigned to more derived species within Aeolosaurini and Saltasaurinae.
... Titanosaurian sauropods were diverse in the latest Cretaceous (Campanian -Maastrichtian) ecosystems of Patagonia (Santucci and Filippi 2022). The current fossil record is heavily biased towards the better sampled Neuquén Group in northern Patagonia, where two major titanosaur lineages are recorded, Colossosauria and Saltasauroidea. ...
... The composition of sauropod assemblages recorded in the Campanian -Maastrichtian of South America varies latitudinally, and several regions have been noted to contain distinct assemblages (Santucci and Filippi 2022). This includes the Brazilian assemblages (Marilia, Serra da Galga, and Adamantina formations), northern Patagonian (Allen, Anacleto, Los Alamitos and Angostura Colorada formations), central Patagonia (Lago Colhué Huapi and La Colonia formations) and southern Patagonian (Chorrillo, Dorotea, and Cerro Fortaleza formations). ...
... Other units from northern Patagonia with more limited exposure, such as the Los Alamitos Formation and Angostura Colorada Formation have also yielded sauropod materials that include records of the genus Aeolosaurus (Powell 1987;Salgado and Coria 1993) and the specimen MACB-RN-147 (Powell 1987). In sum, the sauropod fauna in northern Patagonia during the late Campanian and Maastrichtian has long been recognised as predominantly composed by saltasaurines and aeolosaurines (Santucci and Filippi 2022), as well as other titanosaurians with uncertain affinities (Leanza et al. 2004;Salgado and Bonaparte 2007;García and Salgado 2013;Aranciaga Rolando et al. 2022). This assemblage was recognised as unique within South America and distinct from the faunas of southern Patagonia and those from Brazil. ...
Titanosaurian sauropod dinosaurs were diverse and abundant throughout the Cretaceous, with a global distribution. However, few titanosaurian taxa are represented by multiple skeletons, let alone skulls. Diamantinasaurus matildae, from the lower Upper Cretaceous Winton Formation of Queensland, Australia, was heretofore represented by three specimens, including one that preserves a braincase and several other cranial elements. Herein, we describe a fourth specimen of Diamantinasaurus matildae that preserves a more complete skull—including numerous cranial elements not previously known for this taxon—as well as a partial postcranial skeleton. The skull of Diamantinasaurus matildae shows many similarities to that of the coeval Sarmientosaurus musacchioi from Argentina (e.g. quadratojugal with posterior tongue-like process; braincase with more than one ossified exit for cranial nerve V; compressed-cone–chisel-like teeth), providing further support for the inclusion of both taxa within the clade Diamantinasauria. The replacement teeth within the premaxilla of the new specimen are morphologically congruent with teeth previously attributed to Diamantinasaurus matildae, and Diamantinasauria more broadly, corroborating those referrals. Plesiomorphic characters of the new specimen include a sacrum comprising five vertebrae (also newly demonstrated in the holotype of Diamantinasaurus matildae), rather than the six or more that typify other titanosaurs. However, we demonstrate that there have been a number of independent acquisitions of a six-vertebrae sacrum among Somphospondyli and/or that there have been numerous reversals to a five-vertebrae sacrum, suggesting that sacral count is relatively plastic. Other newly identified plesiomorphic features include: the overall skull shape, which is more similar to brachiosaurids than ‘derived' titanosaurs; anterior caudal centra that are amphicoelous, rather than procoelous; and a pedal phalangeal formula estimated as 2-2-3-2-0. These features are consistent with either an early-branching position within Titanosauria, or a position just outside the titanosaurian radiation, for Diamantinasauria, as indicated by alternative character weighting approaches applied in our phylogenetic analyses, and help to shed light on the early assembly of titanosaurian anatomy that has until now been obscured by a poor fossil record.
A Bacia Bauru congrega um dos mais ricos conjuntos de somatofósseis de tetrá- podes do território brasileiro, sendo cerca de 70% dessa paleodiversidade procedente de seus depósitos em São Paulo. Com registros conhecidos desde o início do século XX, tais fósseis foram coletados em todas as unidades estratigrá cas da Bacia que a oram no estado, i.e., formações Santo Anastácio, Araçatuba, Adamantina (alterna- tivamente dividida em formações Vale do Rio do Peixe, Presidente Prudente e São José do Rio Preto) e Marília. Os grupos registrados incluem raros anuros, mamíferos e escamados, um importante conjunto de testudinos, dinossauros terópodes (incluindo aves) e saurópodes, além de uma das mais diversas faunas de crocodiliformes conhe- cidas para o registro fóssil global. Tal conjunto congrega mais de cinquenta entidades taxonômicas distintas, incluindo 42 espécies formalmente descritas. A partir de dados de cunho bioestratigrá co, incluindo correlação com base em tetrápodes, e poucas da- tações absolutas, a totalidade dos depósitos da Bacia Bauru em São Paulo parece estar cronologicamente restrita ao Neocretáceo, mas um maior detalhamento de tais inferên- cias se faz extremamente necessário. Por m, o histórico das pesquisas com tais fósseis evidencia a importância da interiorização do ensino universitário e do nanciamento público à pesquisa para o avanço da ciência.
The Bauru Basin bears one of the best sampled tetrapod paleofaunas of Brazil, with about 70% of this diversity collected from its deposits in São Paulo. Its fossils are known since the beginning of the 20th century, coming from all stratigraphic units of the Basin cropping-out in the state, i.e., Santo Anastácio, Araçatuba, Adamantina (alternatively divided into Vale do Rio do Peixe, Presidente Prudente, and São José do Rio Preto formations), and Marília formations. Identified taxa include rare anurans, mammals, and squamates, an important set of testudines, theropods (including birds), and sauropods, in addition to one of the most diverse crocodyliform faunas known worldwide. This congregates more than fifty unique taxonomic entities, including 42 formally described species. Based on biostratigraphic correlations (including tetrapods), on few absolute ages, and other sources of evidence, the Bauru Basin deposits in São Paulo seem to be chronologically restricted to the Late Cretaceous, but further investigation is much needed. Finally, the history of research with such fossils highlights the importance of public funding for research and decentralization of university education for the advancement of science.
Our understanding of sauropodomorph evolution is continually improved with the recognition of new species and their inclusion in phylogenetic data sets, along with the incorporation of novel characters. Whereas some subclades remain stable in terms of their original taxonomic content, the definitions of others have proven to be less easily applicable as increased taxon and character sampling has changed sauropodomorph interrelationships. Relatively minor differences in the position of clade specifiers between alternative phylogenies result in substantial differences in clade composition in several instances. Titanosauria is the most successful and diverse clade of sauropodomorph dinosaurs, but its interrelationships are poorly understood. With an ever-growing number of recognized species and increased taxon sampling in phylogenies, resulting in the recovery of newly identified, diverse subclades, the need to re-evaluate titanosaurian supra-specific taxonomy becomes increasingly important. Using fifteen phylogenetic data sets, we conducted a series of analyses to detect the most stable clades and taxa amongst Titanosauria. Based on this, we propose several changes to titanosaur systematics, including a newly defined node-stem triplet composed of Eutitanosauria and its constituent lineages, Colossosauria and Saltasauroidea, developing a new framework to improve stability and facilitate communication of phylogenetic results.
Sauropodomorph dinosaurs were the dominant medium to large-sized herbivores of most Mesozoic continental ecosystems, being characterized by their long necks and reaching a size unparalleled by other terrestrial animals (> 60 tonnes). Our study of morphological disparity across the entire skeleton shows that during the Late Triassic the oldest known sauropodomorphs occupied a small region of morphospace, subsequently diversifying both taxonomically and ecologically, and shifting to a different and broader region of the morphospace. After the Triassic–Jurassic boundary event, there are no substancial changes in sauropodomorph morphospace occupation. Almost all Jurassic sauropodomorph clades stem from ghost lineages that cross the Triassic–Jurassic boundary, indicating that variations after the extinction were more related to changes of pre-existing lineages (massospondylids, non-gravisaurian sauropodiforms) rather than the emergence of distinct clades or body plans. Modifications in the locomotion (bipedal to quadrupedal) and the successive increase in body mass seem to be the main attributes driving sauropodomorph morphospace distribution during the Late Triassic and earliest Jurassic. The extinction of all non-sauropod sauropodomorphs by the Toarcian and the subsequent diversification of gravisaurian sauropods represent a second expansion of the sauropodomorph morphospace, representing the onset of the flourishing of these megaherbivores that subsequently dominated in Middle and Late Jurassic terrestrial assemblages.
Reconstructions of movement in extinct animals are critical to our understanding of major transformations in vertebrate locomotor evolution. Estimates of joint range of motion (ROM) have long been used to exclude anatomically impossible joint poses from hypothesized gait cycles. Here we demonstrate how comparative ROM data can be harnessed in a different way to better constrain locomotor reconstructions. As a case study, we measured nearly 600,000 poses from the hindlimb joints of the Helmeted Guineafowl and American alligator, which represent an extant phylogenetic bracket for the archosaurian ancestor and its pseudosuchian (crocodilian line) and ornithodiran (bird line) descendants. We then used joint mobility mapping to search for a consistent relationship between full potential joint mobility and the subset of joint poses used during locomotion. We found that walking and running poses are predictably located within full mobility, revealing additional constraints for reconstructions of extinct archosaurs. The inferential framework that we develop here can be expanded to identify ROM-based constraints for other animals and, in turn, will help to unravel the history of vertebrate locomotor evolution.
Raman spectroscopy has facilitated rapid progress in the understanding of patterns and processes associated with biomolecule fossilization and revealed the preservation of biological and geological signatures in fossil organic matter. Nonetheless six large-scale statistical studies of Raman spectra of carbonaceous fossils, selected from a number of independent assessments producing similar trends, have been disputed. Alleon et al. applied a wavelet transform analysis in an unconventional way to identify frequency components contributing to two baselined spectra selected from these studies and claimed similarities with a downloaded edge filter transmission spectrum. On the basis of indirect comparisons and qualitative observations they argued that all spectral features detected, including significant mineral peaks, can be equated to edge filter ripples and are therefore artefactual. Alleon et al. extrapolated this conclusion to dispute not only the validity of n>200 spectra in the studies in question, but also the utility of Raman spectroscopy, a well established method, for analysing organic materials in general. Here we test the claims by Alleon et al. using direct spectral comparisons and statistical analyses. We present multiple independent lines of evidence that demonstrate the original, biologically and geologically informative nature of the Raman spectra in question. We demonstrate that the methodological approach introduced by Alleon et al. is unsuitable for assessing the quality of spectra and identifying noise within them. Statistical analyses of large Raman spectral data sets provide a powerful tool in the search for compositional patterns in biomaterials and yield invaluable insights into the history of life.
CT scans of the type braincase of Limaysaurus tessonei (MUCPv-205) allowed the first study of the endocranial cavities (brain and inner ear) for this South American taxon. Comparisons of the cranial endocast of L. tessonei with other sauropods indicate that 1) South American rebbachisaurids are more similar to each other than to Nigersaurus, and 2) certain association of traits are present in all known rebbachisaurid cranial endocasts, such as lack of an enlarged dorsal expansion, poorly laterally projected cerebral hemispheres, presence of a small flocculus of the cerebellum, markedly long passage for the facial nerve (CN VII), markedly inclined pituitary, and presence of a passage for the basilar artery communicating the floor of the endocranial cavity and the pituitary fossa. The relatively enlarged olfactory region indicates that smell was an important sense for this group of dinosaurs, suggesting different olfactory capabilities when compared to coeval titanosaurs.
Throughout their 250 Myr history, archosaurian reptiles have exhibited a wide array of body sizes, shapes, and locomotor habits, especially in regard to terrestriality. These features make Archosauria a useful clade with which to study the interplay between body size, shape, and locomotor behavior, and how this interplay may have influenced locomotor evolution. Here, digital volumetric models of 80 taxa are used to explore how mass properties and body proportions relate to each other and locomotor posture in archosaurs. One-way, nonparametric, multivariate analysis of variance, based on the results of principal components analysis, shows that bipedal and quadrupedal archosaurs are largely distinguished from each other on the basis of just four anatomical parameters ( p < 0.001): mass, center of mass position, and relative forelimb and hindlimb lengths. This facilitates the development of a quantitative predictive framework that can help assess gross locomotor posture in understudied or controversial taxa, such as the crocodile-line Batrachotomus (predicted quadruped) and Postosuchus (predicted biped). Compared with quadrupedal archosaurs, bipedal species tend to have relatively longer hindlimbs and a more caudally positioned whole-body center of mass, and collectively exhibit greater variance in forelimb lengths. These patterns are interpreted to reflect differing biomechanical constraints acting on the archosaurian Bauplan in bipedal versus quadrupedal groups, which may have shaped the evolutionary histories of their respective members.
A recent study by Norell et al. (2020) described new egg specimens for two dinosaur species, identified as the first soft-shelled dinosaur eggs. The authors used phylogenetic comparative methods to reconstruct eggshell type in a sample of reptiles, and identified the eggs of dinosaurs and archosaurs as ancestrally soft-shelled, with three independent acquisitions of a hard eggshell among dinosaurs. This result contradicts previous hypotheses of hard-shelled eggs as ancestral to archosaurs and dinosaurs. Here we estimate the ancestral condition for dinosaur and archosaur eggs by reanalyzing the original data from Norell et al. and that from a recent study on reptile eggshells (Legendre et al., 2020) with the addition of these new dinosaur specimens. We show that the recovery of dinosaur eggs as ancestrally soft-shelled is conditioned by the discretization of a continuous character (eggshell thickness), the exclusion of turtle outgroups from the original sample, and a lack of branch length information. When using a larger sample, calibrated trees, and a definition of hard-shelled eggs referencing their unique prismatic structure, we recover dinosaur and archosaur eggs as either hard-shelled or uncertain (i.e. equal probability for hard- and soft-shelled). This remaining ambiguity is due to uncertainty in the assessment of eggshell type in two dinosaur species, i.e. ~1% of the total sample. We conclude that more reptile egg specimens and a strict comparative framework are necessary to decipher the evolution of dinosaur eggs in a phylogenetic context.
Sauropods, the giant long-necked dinosaurs, became the dominant group of large herbivores in terrestrial ecosystems after multiple related lineages became extinct towards the end of the Early Jurassic (190-174 Ma). The causes and precise timing of this key faunal change, as well as the origin of eusauropods (true sauropods), have remained ambiguous mainly due to the scarce dinosaurian fossil record of this time. The terrestrial sedimentary successions of the Cañadón Asfalto Basin in central Patagonia (Argentina) document this critical interval of dinosaur evolution. Here, we report a new dinosaur with a nearly complete skull that is the oldest eusauropod known to date and provide high-precision U-Pb geochronology that constrains in time the rise of eusauropods in Patagonia. We show that eusauropod dominance was established after a massive magmatic event impacting southern Gondwana (180-184 Ma) and coincided with severe perturbations to the climate and a drastic decrease in the floral diversity characterized by the rise of conifers with small scaly leaves. Floral and faunal records from other regions suggest these were global changes that impacted the terrestrial ecosystems during the Toarcian warming event and formed part of a second-order mass extinction event.
This book documents analyses of the dinosaur nesting sites of the Lameta
Formation at Jabalpur, Districts Dhar and Jhabua, Madhya Pradesh; Districts Kheda
and Panchmahal (Gujarat); and the Pisdura, Dongargaon and Pavna sectors in
the Chandrapur Districts of Maharashtra, which are exposed in India along an east-west
and central axis. In this work, special emphasis has been given to the dinosaur nesting
sites of the east-central Narbada River region, including its regional geology. The work
was undertaken to provide detailed information concerning dinosaur eggs, eggshell
fragments, nests and clutches found in the Lameta Formation along the east-west
and the central Narbada River region of peninsular India. Prior to the present work
there had been no detailed review of systematic work on the taxonomy, micro- and
ultrastructural studies of dinosaur eggs and eggshells from the Lameta Formation.
The study documents the field and laboratory investigations that facilitated
the reconstruction of the morphotaxonomy, models for the burial pattern of eggs
and eggshells, taphonomic implications, and the palaeoenvironmental context and
palaeoecological conditions during the Late Cretaceous at the time of the extrusion
of the Deccan traps, which may have been partly responsible for the extinction
of the dinosaurs. The need to follow a parataxonomic classification for Indian
dinosaur eggs and eggshell types is very apparent, and this book addresses this aspect
in some detail. The emphasis on the application of parataxonomic schemes is based
on the description of new oospecies and their comparison with previously known
forms. The present work has led to the recovery of numerous nests, many collapsed
eggs and hundreds of dinosaur eggshell fragments from the localities situated near
the east, west and central Narbada River regions. It will be of interest to academics and
professional palaeontologists, and all students of dinosaurs.
For over a century, researchers have assumed that the plane of the lateral semicircular canal of the inner ear lies parallel to the horizon when the head is at rest, and used this assumption to reconstruct head posture in extinct species. Although this hypothesis has been repeatedly questioned, it has never been tested on a large sample size and at a broad taxonomic scale in mammals. This study presents a comprehensive test of this hypothesis in over one hundred “ungulate” species. Using CT scanning and manual segmentation, the orientation of the skull was reconstructed as if the lateral semicircular canal of the bony labyrinth was aligned horizontally. This reconstructed cranial orientation was statistically compared to the actual head posture of the corresponding species using a dataset of 10,000 photographs and phylogenetic regression analysis. A statistically significant correlation between the reconstructed cranial orientation and head posture is found, although the plane of the lateral semicircular canal departs significantly from horizontal. We thus caution against the use of the lateral semicircular canal as a proxy to infer precisely the horizontal plane on dry skulls and in extinct species. Diet (browsing or grazing) and head-butting behaviour are significantly correlated to the orientation of the lateral semicircular canal, but not to the actual head posture. Head posture and the orientation of the lateral semicircular canal are both strongly correlated with phylogenetic history.
The Late Jurassic was a period of great diversity for sauropod dinosaurs, with different lineages of Neosauropoda flourishing, including several camarasauromorph taxa. Efforts made in recent years have resulted in a great increase in our current knowledge of basal camarasauromorph evolution, including both the detailed description of new and previously poorly known sauropods and expanded phylogenetic analyses. Although most recent phylogenies converge in their results on early camarasauromorph diversification, the phylogenetic position of Europasaurus, from the Late Jurassic of Germany, remains controversial despite the completeness of the material representing this species. Although Europasaurus was recovered as a relatively basal camarasauromorph in all phylogenetic analyses to date, some of them retrieved this taxon in a slightly more derived position, among basal brachiosaurids. Europasaurus is not only one of the most complete camarasauromorphs but also the first unequivocal dwarf that evolved through paedomorphosis, retaining several plesiomorphic characters, especially in the cranium. Cranial and axial material of Europasaurus has been described in detail but the appendicular skeleton has not. The current paper rectifies this by providing detailed descriptions and illustrations of its appendicular skeleton. In addition, an extensive re-evaluation of the systematic position of Europasaurus was done based on the three most substantial data sets published in recent years. These analyses resolved Europasaurus as a basal camarasauromorph in all cases, but brachiosaurid affinities remain plausible, especially considering the heterochronic evolution of the taxon.
Our knowledge on the anatomy of the first dinosaurs (Late Triassic, 235–205 Ma) has drastically increased in the last years, mainly due to several new findings of exceptionally well-preserved specimens. Nevertheless, some structures such as the neurocranium and its associated structures (brain, labyrinth, cranial nerves, and vasculature) remain poorly known, especially due to the lack of specimens preserving a complete and articulated neurocranium. This study helps to fill this gap by investigating the endocranial cavity of one of the earliest sauropodomorphs, Buriolestes schultzi, from the Upper Triassic (Carnian—c. 233 Ma) of Brazil. The endocranial anatomy of this animal sheds light on the ancestral condition of the brain of sauropodomorphs, revealing an elongated olfactory tract combined to a relatively small pituitary gland and well-developed flocculus of the cerebellum. These traits change drastically across the evolutionary history of sauropodomorphs, reaching the opposite morphology in Jurassic times. Furthermore, we present here the first calculations of the Reptile Encephalization Quotient (REQ) for a Triassic dinosaur. The REQ of B. schultzi is lower than that of Jurassic theropods, but higher than that of later sauropodomorphs. The combination of cerebral, dental, and postcranial data suggest that B. schultzi was an active small predator, able to track moving prey.
The titanosaurian appendicular skeleton exhibits morphological similarities among different clades and its osteological information is usually less taxonomically meaningful than those of other regions of the skeleton. There is a probable morphological convergence due to morphofunctional similarities between members of different titanosaurian groups. In addition, higher intraspecific variability has hindered the assessment of similar forms such as the Late Cretaceous titanosaurians of the Ibero-Armorican domain. The use of 3D-geometric morphometrics and discriminant analyses on an abundant sample of titanosaurian limb elements from the Lo Hueco site and other titanosaurian taxa has been able to characterize the differences between several sauropod clades with the control of the intraspecific variability. Similar methods with the use of surface analyses of other titanosaurs enabled the recognition of morphological similarities congruent with morphofunctional convergences between one of the lithostrotian morphotypes identified in Lo Hueco (the Morphotype II) and some gracile colossosaurs such as Mendozasaurus neguyelap. In contrast, Morphotype I at Lo Hueco present a more typical titanosaurian morphology, resembling Jainosaurus cf. septentrionalis. The use of discriminant analyses allowed us to distinguish Colossosauria on the basis of limb morphology for the first time. We also observed that Colossosauria and Saltasauridae diverge from a more typical titanosaurian non-autopodial limb skeleton. Our results also suggest a highly different and specialized limb skeleton for the Saltasauridae in comparison with other sampled titanosaurians. The use of surface semilandmarks and discriminant analyses also allowed us to propose several new potential osteological characters for use in phylogenetic analyses through the maximization of differences between the sampled clades.
South American titanosaurians have been central to the study of the evolution of Cretaceous sauropod dinosaurs. Despite their remarkable diversity, the fragmentary condition of several taxa and the scarcity of records outside Patagonia and southwestern Brazil have hindered the study of continental-scale paleobiogeographic relationships. We describe two new Late Cretaceous titanosaurians from Quebrada de Santo Domingo (La Rioja, Argentina), which help to fill a gap between these main areas of the continent. Our phylogenetic analysis recovers both new species, and several Brazilian taxa, within Rinconsauria. The data suggest that, towards the end of the Cretaceous, this clade spread throughout southern South America. At the same locality, we discovered numerous accumulations of titanosaurian eggs, likely related to the new taxa. With eggs distributed in three levels along three kilometres, the new site is one of the largest ever found and provides further evidence of nesting site philopatry among Titanosauria.
Narambuenatitan palomoi is a titanosaurian sauropod from the Upper Cretaceous of North Patagonia. Considered initially as a basal titanosaur, this taxon has uncertain phylogenetic relationships within the clade. An X-ray Computed Tomography (CT) scan of the holotype braincase allowed the first reconstruction of the brain and inner ear of this taxon, making it possible to compare the neuroanatomy with that of closely related forms. Except for the slightly sigmodal shape of the endocast in lateral view—considered a basal condition—, the brain shows derived titanosaurian traits such as a poorly developed dorsal expansion and a single exit for Cranial Nerve (CN) XII. In contrast, the inner ear exhibits slender and long semicircular canals (the anterior semicircular canal is distinctly longer than the posterior semicircular canal), which is a character present in more basal representatives of the group, such as Sarmientosaurus. We consider, however, the morphology of the inner ear as an unreliable indicator of phylogenetic position. Furthermore, there is a remarkable similarity between the morphology of the endocast of Narambuenatitan and the possible saltasaurid from (FAM 03.064), from the Upper Cretaceous of Fox-Amphoux-Métisson, France, suggesting saltasaurine affinities for the Argentinean taxon.
Spatiotemporal changes in fossil specimen completeness can bias our understanding of a group's evolutionary history. The quality of the sauropodomorph fossil record was assessed a decade ago, but the number of valid species has since increased by 60%, and 17% of the taxa from that study have since undergone taxonomic revision. Here, we assess how 10 years of additional research has changed our outlook on the group's fossil record. We quantified the completeness of all 307 sauropodomorph species currently considered valid using the skeletal completeness metric, which calculates the proportion of a complete skeleton preserved for each taxon. Taxonomic and stratigraphic age revisions, rather than new species, are the drivers of the most significant differences between the current results and those of the previous assessment. No statistical differences appeared when we use our new dataset to generate temporal completeness curves based solely on taxa known in 2009 or 1999. We now observe a severe drop in mean completeness values across the Jurassic–Cretaceous boundary that never recovers to pre‐Cretaceous levels. Explaining this pattern is difficult, as we find no convincing evidence that it is related to environmental preferences or body size changes. Instead, it might result from: (1) reduction of terrestrial fossil preservation space due to sea level rise; (2) ecological specificities and relatively high diagnosability of Cretaceous species; and/or (3) increased sampling of newly explored sites with many previously unknown taxa. Revisiting patterns in this manner allows us to test the longevity of conclusions made in previous quantitative studies.
Sauropodomorpha were herbivorous saurischian dinosaurs that incorporate Sauropoda and early-diverging sauropodomorphs. The oldest sauropodomorph remains are known from Late Triassic deposits, most of them Gondwanan. The Laurasian record comprises some Triassic forms, but the bulk is Jurassic in age. Among the 14 Jurassic non-sauropodan sauropodomorphs from Laurasia described in the past, 8 are from China. Here we describe a new non-sauropodan sauropodomorph, Irisosaurus yimenensis gen. et sp. nov., from the Early Jurassic Fengjiahe Formation of China. Nearly all of the non-sauropodan sauropodomorph genera currently known from China were first reported from the Lufeng Formation. The Fengjiahe Formation is its Southern equivalent, bringing a fauna similar to that of the Lufeng Formation to light. The new genus is defined based on an incomplete but unique maxilla, with a premaxillary ramus higher than long prior to the nasal process, a large and deep neurovascular foramen within the perinarial fossa, and a deep perinarial fossa defined by a sharp rim. Phylogenetic analysis places Irisosaurus at the very base of Sauropodiformes, as the sister-taxon of the Argentinean genus Mussaurus. This specimen adds to a growing assemblage of Chinese Jurassic non-sauropodan sauropodomorphs that offers new insight into the Laurasian evolution of this clade.
Although sauropodomorph dinosaurs have been known for a long time from the Late Triassic of central Europe, sauropodomorph diversity and faunal composition has remained controversial until today. Here we review sauropodomorph material from the Canton Schaffhausen, Switzerland. The material comes from three different but geographically close localities and represents at least three different taxa. Apart from the common genus Plateosaurus, the material includes remains of two different large, robustly built sauropodomorphs. One of these is described as a new taxon, Schleitheimia schutzi n. gen. et sp., on the basis of an unusual ilium and associated axial and appendicular material. Schleitheimia represents a derived basal sauropodiform and possibly the immediate outgroup to Sauropoda, and thus is the most derived sauropodomorph known from the Late Triassic of Europe. These results thus highlight the diversity of sauropodomorphs in the Late Triassic of central Europe and further indicate widespread sauropodomorph survival across the Triassic-Jurassic boundary.
Rinconsaurus caudamirus, from the Bajo de la Carpa Formation (Santonian), Río Negro, Argentina, is represented by several axial and appendicular elements from, at least, four specimens. The axial skeleton of this taxon was described in detail in a recent contribution, pending a complete analysis and description of its appendicular skeleton. This contribution focuses on the description of the appendicular skeleton of Rinconsaurus and its phylogenetic relationships, considering the new information provided here. Rinconsaurus clearly differs from other titanosaurs for the presence of several autapomorphic characters and for a unique association of characters, some of which are also present in lognkosaurians, aeolosaurines and saltasaurines titanosaurs, and by having a scapula with a scapular blade angled 65° with respect to the coracoid articulation, similar to that of Bellusaurus, Dreadnoughtus and Muyelensaurus. Equations for estimating body mass in sauropods based on long bone circumference suggest a body mass of at least 3-5 tonnes for the largest individuals of Rinconsaurus, being lighter than saltasaurines, but heavier than aeolosaurines. Rinconsaurus was incorporated into an expanded version of a phylogenetic data matrix along with several ontemporary South American titanosaurs. The resulting data matrix comprises 102 taxa scored for 431 characters, and our phylogenetic analysis retrieves Rinconsaurus as a member of the clade Rinconsauria. For its part, the clade Rinconsauria, in which Aeolosaurini is nested, is recovered within a diverse Lognkosauria. When the resulting trees are time calibrated and taking into account the position of Ninjatitan within Rinconsauria, there results that the possible origin of the clades Lognkosauria and Rinconsauria (among other titanosaur clades) could have occurred towards the beginning of the Early Cretaceous.
We present a detailed histological study of long bones from an ontogenetic series of Mussaurus patagonicus, an early sauropodomorph from the Lower Jurassic of Argentina. Twenty long bones, including humeri, femora and fibulae, obtained from 13 individuals of different body sizes were sampled for histological analysis. In general terms, the cortical bone is formed by a well vascularized fibrolamellar and parallel fibred bone. Except for the smaller individuals, cyclical growth marks (CGMs) are well recorded in all the specimens but their number and relative position is highly variable. Mussaurus exhibits marked variation regarding relative growth rate, with some individuals growing much faster than others. Such variation affects the size of the adult individuals, which results in a poor correlation between the body size and the age/ontogenetic stage for this taxon. These discrepancies may be related to sexual dimorphism and/or developmental plasticity. Intraspecific variation is also recorded with regard to the growth strategies, which can vary from cyclical, as in other early sauropodomorphs, to continuous, as reported in sauropods. Sexual maturity appears to have been reached between 23 and 31 years, which is delayed in comparison to other early sauropodomorphs but more comparable with derived sauropods. The attainment of somatic maturity appears to have been reached at about 14 years after onset of sexual maturity. Mussaurus is a sauropodiform, phylogenetically closer to sauropods than most other Early Jurassic sauropodomorphs, and therefore provides critical information for understanding palaeobiological aspects of the origin of sauropods and the onset of gigantism in this lineage.
Early sauropodomorphs were diverse in Gondwana, being particularly well represented in South America. Mussaurus patagonicus is one of the best-known non-sauropod sauropodomorphs that inhabited the Southern Hemisphere. Its importance relies on its phylogenetic position close to Sauropoda and also because it is known from a well-represented ontogenetic series, including embryos, neonate and late immature skeletons, which are particularly scarce among sauropodomorphs. In this regard, Mussaurus represents an excellent opportunity to explore anatomical and palaeobiological constraints during the ontogeny of early stages of the evolution of the group. We present the osteology of the postcranial skeleton of immature specimens of Mussaurus, highlighting the main anatomical changes that occurred during its ontogeny. The phylogenetic position of this taxon based on mature specimens is evaluated through a parsimony analysis, corroborating its position as closer to Sauropoda than most other early sauropodomorphs. Immature stages of this taxon were also evaluated phylogenetically, showing an overall phylogenetic signal that positioned them closer to the root of Sauropodomorpha than the mature specimens. However, the cranial and some postcranial anatomical partitions of neonates and late immature specimens have different phylogenetic signals, showing derived traits present in Sauropoda and related taxa (and supporting the hypothesis of paedomorphic evolution in certain regions of the skeleton). Our analysis shows that most of the appendicular apomorphies in Mussaurus appear late in ontogeny, whereas axial characters (in particular for OS 1), including those of the skull and the presacral vertebrae, show derived character states early in ontogeny that are congruent with the phylogenetic position of mature specimens. Ontogenetic series of other sauropodomorph species, however, are required to test if this pattern applies to the entire group.
An isolated vertebra from the Late Cretaceous of Uzbekistan (Asia), previously interpreted as a titanosaur anterior caudal, was recently assigned as the holotype and unique specimen of a new rebbachisaurid taxon, Dzharatitanis kingi. This record would drastically impact both biogeographical and chronological aspects of the group. As some of the characters identified for such systematic assignment seem to have been incorrectly scored and/or have a more widespread distribution amongst Neosauropoda, we revised and discussed them in depth to verify the putative rebbachisaurid affinities of this taxon. The phylogenetic analyses carried out recovered Dzharatitanis as a titanosaur sauropod, most probably related to Lognkosauria. The extra steps needed to force Dzharatitanis within Rebbachisauridae confirms that its titanosaur affinity is not solely the most parsimonious hypothesis but also is well supported when the incompleteness of the material is considered. Given this new phylogenetic position, a new modified diagnosis is provided here. Although more complete evidence is needed, the reinterpretation of Dzharatitanis as a titanosaur with lognkosaurian affinities suggests a wider biogeographic distribution of this group of colossosaurs during the Cretaceous. At present, there is no reliable evidence to assume that rebbachisaurid sauropods have inhabited Asia.
Pellegrinisaurus powelli is a large titanosaurian sauropod from the Upper Cretaceous of northern Patagonia (Río Negro Province, Argentina). The holotype of this species comprises an incomplete femur, four dorsal and 26 caudal vertebrae collected from the Lago Pellegrini locality. A single middle caudal vertebra from the nearby Cinco Saltos locality has been more recently referred to Pellegrinisaurus. With the purpose of increasing our knowledge about the titanosaur faunas of the Upper Cretaceous of Patagonia, here we provide a detailed redescription of the holotype and referred specimens of Pellegrinisaurus, reviewing its diagnosis and phylogenetic position. A histological analysis of the femur of the holotype is also carried out. The diagnostic characters originally proposed for Pellegrinisaurus are here considered invalid because they either correspond with diagenetic deformations of the specimen or are present in other titanosaurs. The new diagnostic features are related with the presence of large lateral blind fossae with distinct dorsal rims in the anterior caudal centra and with a low longitudinal ridge on the posterior side of the femur shaft originated from the trochanteric shelf and extending to the distal third of the shaft. The phylogenetic analysis recovers Pellegrinisaurus as a non-saltasaurid lithostrotian, closely related with Alamosaurus sanjuanensis. The bone histology indicates that the holotype corresponds to a subadult (i.e. sexually mature but still growing) individual. Finally, the caudal vertebra previously attributed to Pellegrinisaurus cannot be referred to this genus and is here assigned to Titanosauria indet.
Eggshells represent an important part of the fossil record of Titanosauria (Dinosauria – Neosauropoda) and their stable isotope compositions are valuable palaeoenvironmental proxies. A new set of conventional (δ¹⁸O and δ¹³C) and clumped (Δ47) stable isotope compositions of titanosaurian eggshells is presented, together with that of a bone and a single associated tooth, sampled in three Late Cretaceous nesting sites from La Rioja Province, NW Argentina. The preservation state of the fossils was first evaluated using optical and analytical techniques, such as transmitted light and optical cathodoluminescence (CL) microscopy, energy dispersive X-ray spectroscopy (EDX), and laser ablation-inductively coupled plasma-mass spectrometry (LA-ICP-MS). The isotopic compositions of the fossils were then compared to those of associated carbonate rocks and nodules, hydrothermal calcite and quartz, and those reported for eggshells from other nesting sites worldwide. This large, combined sample set allows us to define an isotopic hallmark (δ¹³CVPDB = −15 to −11‰; δ¹⁸OVSMOW = 27 to 33‰) typical for well-preserved mid-palaeolatitude titanosaurian eggshells. This hallmark is intended to identify the oological specimens best suited for palaeoenvironmental reconstructions, for instance in museum collection samples that may lack associated abiogenic materials such as host rocks. In addition, our isotopic data support that titanosaurians were animals with an elevated body temperature, mainly feeding on C3 plants, and reproducing under conditions more arid than the long-term average. The data are in excellent agreement with the isotopic data reported from other mid-palaeolatitude nesting sites around the world, indicating that titanosaurians needed similar environmental conditions to reproduce, regardless of the palaeogeographic location of their habitat. Finally, we raise the question whether titanosaurians experienced reproduction-related fasting, as noted for several extant vertebrates, and discuss the complexity of interpreting Δ47-derived temperatures, despite very consistent bulk isotopic data.
The ichnological Cretaceous sauropod record of South America is analyzed for the first time in relation with skeletal and paleoenvironmental data. The updated database includes 39 tracksites and 71 valid species (53 titanosaurs and 18 non-titanosaurs) from Colombia, Ecuador, Peru, Chile, Brazil and Argentina. The track and bone records analyzed evidence a relationship with continental environments, specifically with fluvial ones. This is observed in all Sauropoda records, indicating an ecological association of the Cretaceous sauropods for these environments. In addition, the paleogeographic reconstruction integrating these records does not evidence any correlation between the distribution of sauropods and the latitudinal range. During the late Campanian–Maastrichtian interval, when the Atlantic transgression event was established, the titanosaur record started to show a singular panorama. The tracksites are preserved not only in continental paleoenvironments but also in marginal-marine ones, being the only last records of titanosaurs associated with that environment in South America. Both the paleoecological aspects based on sauropod Cretaceous record and the paleoenvironmental data collected in this work support the hypothesis that these tracksites were used by titanosaurs as ‘transit areas’ to move among the environments they inhabited.
The holotype of the titanosaur sauropod Rinconsaurus caudamirus, from the Bajo de la Carpa Formation (Santonian, Upper Cretaceous, Neuquén Group), is based on an articulated series of 13 anterior-middle to middle posterior caudal vertebrae and two illia, in addition to cranial, axial and appendicular elements corresponding to several individuals. One of the skull elements originally identified as a prefrontal (MAU-Pv-CRS-102), is reinterpreted here as a mesoeucrocodylian right ilium, likely belonging to Pehuenchesuchus enderi, a crocodyliform found in the same quarry. Therefore, this element is excluded from the Rinconsaurus type materials, adding a new element to Pehuenchesuchus and increasing the knowledge of its anatomy.
The titanosaur sauropod record of Patagonia, mainly recovered from Upper Cretaceous strata, is probably the richest worldwide. Here
we present a new sauropod dinosaur, Ninjatitan zapatai gen. et sp. nov., from the Lower Cretaceous Bajada Colorada Formation (Berriasian–
Valanginian) of north Patagonia (Neuquén Province, Argentina), from which postcranial remains are preserved. The anatomical analysis and com-
parisons performed in this specimen evidence strong affinity with titanosaur sauropods. This assumption is corroborated with the inclusion of
the new taxon in an updated phylogenetic data matrix. The cladistic analyses indicate that Ninjatitan could be considered the earliest known
titanosaur sauropod. The combination of features such as the presence of procoelous anterior caudal centra, the pneumatized neural arch of
anterior caudal vertebrae, and the posterodorsal border of the scapular acromion near the glenoid level supports its titanosaur affinities. The
presence of a basal titanosaurian sauropod in the lowermost Cretaceous of Patagonia supports the hypothesis that the group was established
in the Southern Hemisphere and reinforces the idea of a Gondwanan origin for Titanosauria. The Bajada Colorada sauropod fauna represents
one of the most diverse and unique associations from the lowermost Cretaceous worldwide recorded.
A new lithostrotian sauropod, Arackar licanantay gen. et sp. nov. is described based on a partial skeleton from the Upper Cretaceous (CampanianeMaastrichtian) beds of the Hornitos Formation, Atacama Region, northern Chile. The holotype consists of axial (cervical and dorsal vertebrae) and appendicular (humerus, femur and ischium) elements of a sub-adult specimen (ca. 6.3 m long). Autapomorphies
characterizing this new titanosaur include: middle neural arches with wide and tall centroprezygapophyseal fossa þ parapophyseal centroprezygapophyseal fossa (cprf þ pacprf) extending on
the entire anterior faces of the pedicles, but not above the neural canal, and reduced spinopostzygapophyseal laminae, shorter than the postzygapophyseal facet length. A phylogenetic analysis based on a
data matrix of 87 taxa and 405 characters recovered Arackar as a derived lithostrotian titanosaur, placing it in a clade that includes Rapetosaurus þ (Arackar þ Isisaurus). This is the third dinosaur named from Chile and the third titanosaur from the western side of the Andes in South America.
Osteoderms (ossified dermal elements) are among the most distinctive features of Titanosauria, a spe-ciose clade of Cretaceous sauropods. Though osteoderms are often described as armor, hollow osteo-derms have also been interpreted as mineral storage sites. A new specimen (TMM 45888-1) from the Upper Cretaceous Javelina Formation, Big Bend National Park, Texas, provides insights into osteoderm structure and function. It is oval with a cusp at one end and grooved marginal ornamentation, resembling certain specimens from Argentina but without a keel. It is not divided into bulb and root regions. TMM 45888-1 is the first titanosaur osteoderm from Texas. It cannot be referred to a species but is similar to the osteoderms of Alamosaurus, the only known titanosaur from North America.
X-ray CT scans reveal that the interior of TMM 45888-1 is not hollow. Large neurovascular channels connect foramina on the deep, superficial, and marginal faces. The channels are concentrated along the deep face, at the ends, and passing through the center from deep to superficial. The osteoderm was potentially capable of providing mineral storage, localized defense, and display functions based on its vasculature, material properties, and shape. Whole-body defense, vertebral stabilization, and thermo-regulation are rejected as functions based on apparent osteoderm scarcity, lack of articulations, and limited superficial vasculature. Osteoderms vary in gross and interior morphology among lithostrotians, necessitating caution when generalizing functions across the clade.
Widespread preservation of fossilized biomolecules in many fossil animals has recently been reported in six studies, based on Raman microspectroscopy. Here, we show that the putative Raman signatures of organic compounds in these fossils are actually instrumental artefacts resulting from intense background luminescence. Raman spectroscopy is based on the detection of photons scattered inelastically by matter upon its interaction with a laser beam. For many natural materials, this interaction also generates a luminescence signal that is often orders of magnitude more intense than the light produced by Raman scattering. Such luminescence, coupled with the transmission properties of the spectrometer, induced quasi‐periodic ripples in the measured spectra that have been incorrectly interpreted as Raman signatures of organic molecules. Although several analytical strategies have been developed to overcome this common issue, Raman microspectroscopy as used in the studies questioned here cannot be used to identify fossil biomolecules.
The titanosaurian sauropod dinosaur Diamantinasaurus matildae is represented by two individuals from the Cenomanian-lower Turonian 'upper' Winton Formation of central Queensland, northeastern Australia. The type specimen has been described in detail, whereas the referred specimen, which includes several elements not present in the type series (partial skull, atlas, axis and postaxial cervical vertebrae), has only been described briefly. Herein, we provide a comprehensive description of this referred specimen, including a thorough assessment of the external and internal anatomy of the braincase, and identify several new autapomorphies of D. matildae. Via an expanded data matrix consisting of 125 taxa scored for 552 characters, we recover a close, well-supported relationship between Diamantinasaurus and its contemporary, Savannasaurus elliottorum. Unlike previous iterations of this data matrix, under a parsimony framework we consistently recover Diamantinasaurus and Savannasaurus as early-diverging members of Titanosauria using both equal weighting and extended implied weighting, with the overall topology largely consistent between analyses. We erect a new clade, named Diamantinasauria herein, that also includes the contemporaneous Sarmientosaurus musacchioi from southern Argentina, which shares several cranial features with the referred Diamantinasaurus specimen. Thus, Diamantinasauria is represented in the mid-Cretaceous of both South America and Australia, supporting the hypothesis that some titanosaurians, in addition to megaraptoran theropods and possibly some ornithopods, were able to disperse between these two continents via Antarctica. Conversely, there is no evidence for rebbachisaurids in Australia, which might indicate that they were unable to expand into high latitudes before their extinction in the Cenomanian-Turonian. Likewise, there is no evidence for titanosaurs with procoelous caudal vertebrae in the mid-Cretaceous Australian record, despite scarce but compelling evidence for their presence in both Antarctica and New Zealand during the Campanian-Maastrichtian. These later titanosaurs presumably dispersed into these landmasses from South America before the Campanian (~85 Mya), when seafloor spreading between Zealandia and Australia commenced. Although Australian mid-Cretaceous dinosaur faunas appear to be cosmopolitan at higher taxonomic levels, closer affinities with South America at finer scales are becoming better supported for sauropods, theropods and ornithopods.
A stegosaurian humerus from the Oxfordian–Tithonian(?) Cañadón Calcáreo Formation of Chubut, Argentina, extends the fossil record of this clade of thyreophoran ornithischian dinosaurs to the Upper Jurassic of South America. The element shares the derived character of an oblique ridge extending from the deltopectoral crest towards the medial distal condyle with taxa such as Kentrosaurus and Stegosaurus and thus represents a derived representative of the clade. The presence of stegosaurs in the Cañadón Calcáreo Formation underlines the similarities of its dinosaur fauna with other Late Jurassic dinosaur faunas, such as the Morrison Formation of North America or the Tendaguru Formation of Tanzania, in at least broad systematic terms.
Sauropodomorpha is the first major dinosaurian group that radiated during the Triassic. During this time the group underwent major changes in body plan, including the acquisition of features related to herbivory, large body size, and quadrupedality. By the end of the Late Triassic, approximately 30 million years after the origin of dinosaurs, sauropodomorphs predominated the niches of large herbivores in continental ecosystems throughout the world. The Triassic sauropodomorph diversity includes diverse lineages with great disparity in body size, feeding biomechanics, and locomotion types, ranging from small (∼10 kg) bipedal taxa to the large (>5 tons) quadrupedal lessemsaurids. The South American record has provided key information to understand certain stages of this evolutionary radiation. We review here the diversity and composition of sauropodomorph faunas throughout the Late Triassic of South America and highlight their contribution for understanding the evolution of this group.
One of the most fascinating research topics in the field of sauropod dinosaurs is the evolution of gigantism. In the particular case of Titanosauria, the record of multi-ton species (those exceeding 40 tons) comes mainly from Patagonia. The record of super-sized titanosaur sauropods has traditionally been extremely fragmentary, although recent discoveries of more complete taxa have revealed significant anatomical information previously unavailable due to preservation biases. In this contribution we present a giant titanosaur sauropod from the Candeleros Formation (Cenomanian, circa 98 Ma) of Neuquén Province, composed of an articulated sequence of 20 most anterior plus 4 posterior caudal vertebrae and several appendicular bones. This specimen clearly proves the presence of a second taxon from Candeleros Formation, in addition to Andesaurus, and is here considered one of the largest sauropods ever found, probably exceeding Patagotitan in size. While anatomical analysis does not currently allow us to regard it as a new species, the morphological disparity and the lack of equivalent elements with respect to coeval taxa also prevent us from assigning this new material to already known genera. A preliminary phylogenetic analysis places this new specimen at the base of the clade leading to Lognkosauria, in a polytomy with Bonitasaura. The specimen here reported strongly suggests the co-existence of the largest and middle-sized titanosaurs with small-sized rebbachisaurids at the beginning of the Late Cretaceous in Neuquén Province, indicating putative niche partitioning. This set of extremely large taxa from Patagonia has contributed to a better understanding of the phylogenetic relationships of titanosaurs, revealing the existence of a previously unknown lineage and shedding new light on body mass evolution.
An additional anterior caudal vertebra of a titanosaurian sauropod Tengrisaurus starkovi from the Lower Cretaceous (Barremian–Aptian) Murtoi Formation of Transbaikalia, Asiatic Russia, reveals new morphological details of this taxon. The new characters include dorsoventrally compressed cotyle and condyle of the centrum and a prominent ridge separating the condyle from the rest of the centrum with the ventral triangular plate (autapomorphy). Parsimony phylogenetic analysis places Tengrisaurus in the predominantly Gondwanan clade Colossosauria + Epachthosaurus on the strict consensus tree and as the sister taxon to the Colossosauria on 66% of the most parsimonious trees. Among Colossosauria, Tengrisaurus is similar with Normanniasaurus from the Albian of France by having a dorsoventrally compressed condyle circumscribed by a distinct ridge, a distinct depression anteroventral to the postzygapophysis, and a deep depression within the postspinal fossa. This discovery suggests that ancestors of the clade Colossosauria were widely distributed in Eurasia during the Early Cretaceous and the clade becomes restricted to the southern continents in the Late Cretaceous.
The last stage of activity of the Ischigualasto–Villa Unión Rift Basin in west-central Argentina is represented by the 1100-m-thick fluvial red-beds of the Los Colorados Formation (Norian). Facies and architectural-element analysis were applied and vertical stacking patterns evaluated in the Los Colorados Formation to develop a depositional model for the postrift stage of basin fill. The Los Colorados Formation is subdivided into eleven stratigraphic intervals, generally characterized by multistory and multilateral channelized bodies interspersed with thick floodplain deposits developed under seasonal semihumid to semiarid climate conditions. The evolution of the fluvial architectural style shows changes in the location of channel facies concentration, in paleocurrents, and sediment provenance from the sixth stratigraphic interval toward the upper part of the Los Colorados Formation. The fluvial architecture observed in the upper part exhibits a drift in paleocurrents from a SE to a NE mean direction, together with a radial pattern in paleocurrent directional data. Thus, the paleoenvironmental evolution of the Los Colorados Formation is interpreted in terms of axial vs. transverse drainage system fluvial architecture under ongoing postrift conditions. While the fluvial architecture of the lower part responds to an axial fluvial system, the upper part is compatible with the entrance of a fluvial transverse drainage system. The role of axial vs. transverse drainage systems is discussed in the Los Colorados Formation paleoenvironmental evolution. Despite the axial system being considered the main sediment feeder of the basin fill in most interpretations of the rock record, our results indicate that transverse drainage systems can play a central role in postrift basin filling, as is proposed in modern examples.
The holotypic materials of the sauropod ‘Morosaurus’ agilis—a partial skull, proatlases, and first three cervical vertebrae—have been a taxonomic and phylogenetic mystery since their initial description by O. C. Marsh in 1889 and redescription by C. W. Gilmore in 1907. Although most species of Morosaurus were subsumed into Camarasaurus in 1919, ‘M.’ agilis was left in the defunct genus without a proper taxonomic assignment. Similarities have been noted between ‘M.’ agilis and other Morrison Formation sauropod taxa, including Camarasaurus, Haplocanthosaurus, Diplodocus, and Brachiosauridae, but it had yet to be included in a phylogenetic analysis. Here we present new data following additional preparation and study that suggest ‘M.’ agilis is a basally diverging member of Dicraeosauridae, along with the recently described sauropod Kaatedocus. Based upon its recovery as a distinct taxon, we propose that ‘M.’ agilis receive the new generic name Smitanosaurus, yielding the new combination Smitanosaurus agilis.
http://zoobank.org/urn:lsid:zoobank.org:pub:6977D649-EE6B-42EE-9E1C-C043A38AC2AC
Remains of Garrigatitan meridionalis nov. gen. et sp. were found in two bonebeds of sequence 2 from the upper Campanian site of Velaux-La Bastide Neuve (Aix-en-Provence Basin, Bouches du Rhône department). The vertebrate assemblage is dominated by dinosaurs, including the titanosaur Atsinganosaurus velauciensis. Garrigatitan meridionalis presents three diagnostic characters: hourglass-shaped humeri (proximal and distal thirds of almost the same transversal width) in anterior and posterior views, ilium with a broad rounded hollow slightly posterior to the base of the pubic peduncle, proximolateral margin of the femur only slightly medially deflected. Garrigatitan was a small to medium-sized sauropod (sub/adult individuals between 4–6 metres and 2–2.5 tonnes), showing anatomical differences with Atsinganosaurus, and with the other Late Cretaceous Ibero-Armorican titanosaurs. Large titanosaurian specimens found at Velaux-La Bastide Neuve could belong to adult Garrigatitan individuals reaching a body length of at least 12 metres. Histological analysis of long bones shows features similar to other Late Cretaceous European titanosaurs, indicating that all individuals had reached skeletal maturity (presence of an EFS, heavy remodelling HOS 12 to 14). The new taxon is recovered within the clade Lirainosaurinae. Garrigatitan meridionalis increases the diversity of Late Cretaceous titanosaurs within the Ibero-Armorican Island.
The application of Fission-Track Thermochronology (FTT), and U-Pb and Lu-Hf isotope analyses on the same zircon grains revealed the provenance and thermal/tectonic events related to the build-up and evolution of the Bauru Basin filling in Minas Gerais, Brazil. The U-Pb on detrital zircon reveals that the potential source areas were dominated by Brasiliano outcrops and subordinately, Paleoproterozoic, Mesoproterozoic, and Carboniferous sources. Positive eHf(t) signatures can characterize the Goiás magmatic Arc and older adjacent terranes as the most probable region that supplied the Bauru Basin. The FTT data display five main age peaks at 569, 337, 235, 132, and 83 Ma. They record the exhumation and denudation processes of Brasiliano and Gondwanide orogens and later, the Serra Geral magmatism of the South American Platform. A younger subordinate age (100–80 Ma) is recorded, and it may be associated with intense alkaline magmatism that occurred during the initial stages of basin deposition.
We present an update and a review of the Late Cretaceous dinosaur tracksites of Bolivia. The Puca Group (Coniacian – Late Maastrichtian) records the tracks and trackways of two different titanosaurid sauropods, ankylosaurs, hadrosaurs and different theropod groups from the Central Andean lacustrine back arc basin. We review the sites from the Maragua syncline (Chuquisaca) and present new data on the famous Toro Toro site (Potosi).
Furthermore, the first complete map of the world’s largest dinosaur tracksite, Cal Orck’o (El Molino Formation, Sucre) gives an insight into behavior and movement patterns. Parallel trackways of subadult ankylosaurs provide the first unequivocal evidence of social behavior amongst these dinosaurs worldwide. The El Molino Formation and the coeval deposits of Southern Peru and Northern Argentina form a megatracksite with a size of around 100,000 km2. The paleogeographic position of the main sites within the basin suggests that they are part of a seasonal migration route along the shoreline and deltas of an ancient lake system.
The morphostructural diversity of Indian, French and Argentinean eggshells has been compared and reviewed in great detail and a serious attempt has been made to evaluate their parataxonomy. Indian and French eggshell oospecies show a close resemblance between five Indian and four French oospecies (Megaloolithus khempurensis = M. siruguei; Megaloolithus jabalpurensis = M. mamillare; M. cylindricus = M. siruguei and M. microtuberculata; Fusioolithus padiyalensis = M. microtuberculata; F. baghensis = M. pseudomamillare). Examination of four oospecies from India and Argentina uncovers three groupings, which show similarity between megaloolithids and fusioolithids of the two continents (Fusioolithus baghensis = Patagoolithus salitralensis; Megaloolithus megadermus = Tipo 1e; M. cylindricus = Tipo 1d; M. jabalpurensis = Tipo 1e). The biomineralization aspects of Indian eggshells or any calcified tissue with dental enamel have been compared and studied at four levels (crystallite, unit, morphostructural and megascopic levels). The dinosaur nests, eggs and eggshell fragments are found to be diagenetically altered by calcite recrystallization (herringbone pattern) and chertified silica, which has been commonly noticed in the pores and pore canals.
Sauropod tracks, particularly those attributable to the ichnogenus Brontopodus are becoming increasingly well known in the Jurassic and Cretaceous of China. Globally there are indications that wide gauge forms, attributable to titanosauriform sauropods increase in the Cretaceous. However, differentiating wide and narrow gauge, broadly categorized as large manus (low heteropody) Brontopodus or small manus (high heteropody) Parabrontopodus, respectively is complicated by the occurrence of intermediate forms with medium gauge and intermediate heteropody, and the unknown role played by size variation. We here describe two morphotypes from the Jurassic-Cretaceous boundary sequences of the Tuchengzi Formation of western Liaoning that are medium sized and mainly distinguished by striking variations in manus rotation angles. Currently Brontopodus birdi from the Lower Cretaceous of North America is typified by wide gauge and low manus rotation (~10°), whereas Brontopodus pentadactylus from the Lower Cretaceous of Korea is characterized by high outward rotation (~90°). We consider such large differences in footprint rotation could be useful in distinguishing morphotypes and diagnostic gaits in sauropod ichnology as they have proven to be in the case of some other dinosaurs. The trackways from the Tuchengzi Formation and their peculiar patterns are a useful basis and starting point for future discussions on the ichnotaxonomy of sauropod trackways.
The titanosaurian sauropod dinosaur Savannasaurus elliottorum is represented by a partial postcranial skeleton from the lower Upper Cretaceous (Cenomanian-lowermost Turonian) Winton Formation of Queensland, northeast Australia. Here, we present a detailed description of this specimen, as well as an emended diagnosis for this titanosaur. Savannasaurus elliottorum displays numerous character states that are generally regarded as plesiomorphic for Titanosauria, as well as several traits that are often regarded as apomorphic of that clade or a less inclusive subset thereof. Several features of Savannasaurus support a close relationship with the coeval Diamantinasaurus matildae, and this clade appears to occupy an early-branching position within Titanosauria. Relative to body size, the thoracic and abdominal breadth of Savannasaurus is greater than that seen in giant titanosaurs such as the contemporaneous South American lognkosaurians; however, this relative breadth is not quite as extreme as that of the small-bodied latest Cretaceous saltasaurines, or Opisthocoelicaudia skarzynskii. The possible advantages engendered by the barrel-shaped thorax, robust limbs, wide-gauge gait, and lack of hyposphene-hypantrum articulations are explored, and it is hypothesized that these traits were positively selected by the wet, temperate floodplain environment in which Savannasaurus lived. Greater stability and flexibility might have reduced the risk of bogging, and/or facilitated more expedient self-extraction from muddy waterholes. Similar environmental pressures acting upon other titanosaurian taxa or clades elsewhere might have led to the repeated independent development, or accentuation, of the bauplan regarded as 'typical' for the clade Titanosauria. This would explain the many observed convergences between Savannasaurus and Diamantinasaurus, and Saltasauridae.. 2020. Osteology of the wide-hipped titanosaurian sauropod dinosaur Savannasaurus elliottorum from the Upper
Its huge size, excellent preservation, and completeness make Patagotitan mayorum a unique opportunity to explore the anatomy, paleobiological, and phylogenetic aspects linked to gigantism within Sauropoda. In this regard, we describe the appendicular skeleton of this titanosaurian species from the late Albian-aged Cerro Barcino Formation of Chubut Province, Argentina. The diagnosis of Patagotitan mayorum is revised, increasing the number of identified autapomorphies (i.e., lateral surface of the scapular blade with two divergent crests; anterior surface of proximal humerus with paired muscle scars; combined bulges on the deltopectoral area of the humerus; ischium with well-developed and sharp ridge projecting from the ischial tuberosity to the distal blade). Several diagnostic characters of this species correspond to osteological correlates associated to appendicular musculature (e.g., Mm. deltoideus scapularis, deltoideus clavicularis, and teres major; M. coracobrachialis; Mm. supracoracoideus/deltoideus clavicularis and latissimus dorsi; Mm. flexor tibialis 3 and adductor femoris 2), which we discuss in the context of sauropod evolution. In the light of a modification of the scaling equation previously proposed and adjusting the long bone circumference for the humeri of Patagotitan, a new body mass estimate of this species ranges between 42-71 tons, with a mean value of 57 tons. Although considerably less than the value obtained by the original linear equation, the corrected quadratic equation used here provides a mean body mass estimate that is more consistent with those derived from volumetric reconstructions of Patagotitan.
Inferring the body mass of fossil taxa, such as non‐avian dinosaurs, provides a powerful tool for interpreting physiological and ecological properties, as well as the ability to study these traits through deep time and within a macroevolutionary context. As a result, over the past 100 years a number of studies advanced methods for estimating mass in dinosaurs and other extinct taxa. These methods can be categorized into two major approaches: volumetric‐density (VD) and extant‐scaling (ES). The former receives the most attention in non‐avian dinosaurs and advanced appreciably over the last century: from initial physical scale models to three‐dimensional (3D) virtual techniques that utilize scanned data obtained from entire skeletons. The ES approach is most commonly applied to extinct members of crown clades but some equations are proposed and utilized in non‐avian dinosaurs. Because both approaches share a common goal, they are often viewed in opposition to one another. However, current palaeobiological research problems are often approach specific and, therefore, the decision to utilize a VD or ES approach is largely question dependent. In general, biomechanical and physiological studies benefit from the full‐body reconstruction provided through a VD approach, whereas large‐scale evolutionary and ecological studies require the extensive data sets afforded by an ES approach. This study summarizes both approaches to body mass estimation in stem‐group taxa, specifically non‐avian dinosaurs, and provides a comparative quantitative framework to reciprocally illuminate and corroborate VD and ES approaches. The results indicate that mass estimates are largely consistent between approaches: 73% of VD reconstructions occur within the expected 95% prediction intervals of the ES relationship. However, almost three quarters of outliers occur below the lower 95% prediction interval, indicating that VD mass estimates are, on average, lower than would be expected given their stylopodial circumferences. Inconsistencies (high residual and per cent prediction deviation values) are recovered to a varying degree among all major dinosaurian clades along with an overall tendency for larger deviations between approaches among small‐bodied taxa. Nonetheless, our results indicate a strong corroboration between recent iterations of the VD approach based on 3D specimen scans suggesting that our current understanding of size in dinosaurs, and hence its biological correlates, has improved over time. We advance that VD and ES approaches have fundamentally (metrically) different advantages and, hence, the comparative framework used and advocated here combines the accuracy afforded by ES with the precision provided by VD and permits the rapid identification of discrepancies with the potential to open new areas of discussion.
The first dinosaur embryos found inside megaloolithid eggs from Auca Mahuevo, Patagonia, were assigned to sauropod dinosaurs that lived approximately 80 million years ago. Discovered some 25 years ago, these considerably flattened specimens still remain the only unquestionable embryonic remains of a sauropod dinosaur providing an initial glimpse into titanosaurian in ovo ontogeny. Here we describe an almost intact embryonic skull, which indicates the early development of stereoscopic vision, and an unusual monocerotic face for a sauropod. The new fossil also reveals a neurovascular sensory system in the premaxilla and a partly calcified braincase, which potentially refines estimates of its prenatal stage. The embryo was found in an egg with thicker eggshell and a partly different geochemical signature than those from the egg-bearing layers described in Auca Mahuevo. The cranial bones are comparably ossified as in previously described specimens but differ in facial anatomy and size. The new specimen reveals significant heterochrony in cranial ossifications when compared with non-sauropod sauropodomorph embryos, and demonstrates that the specialized craniofacial morphology preceded the postnatal transformation of the skull anatomy in adults of related titanosaurians.
Despite continuous improvements, our knowledge of the palaeoneurology of sauropod dinosaurs is still deficient. This holds true even for Titanosauria, which is a particularly speciose clade of sauropods with representatives known from numerous Cretaceous sites in many countries on all continents. The data currently available regarding the palaeoneurology of titanosaurs is strongly biased towards Gondwanan forms (Argentina above all, but also India, Malawi and Australia). In contrast, the palaeoneurology of Laurasian titanosaurs is known only from a few taxa from Spain and Uzbekistan, despite the discovery in other countries of Laurasia of a number of neurocranial remains that would lend themselves well to investigations of this kind. To fill in this gap in our knowledge, we subjected a titanosaurian braincase from the uppermost Upper Cretaceous of southern France to X-ray computed tomographic scanning, allowing the generation of 3D renderings of the endocranial cavity enclosing the brain, cranial nerves and blood vessels, as well as the labyrinth of the inner ear. These reconstructions are used to clarify the phylogenetic position of the specimen from the Fox-Amphoux-Métisson site. A combination of characters, including the presence of two hypoglossal rami on the endocast, the average degree of development of the dorsal-head/caudal-middle-cerebral vein system and the relatively short and subequal lengths of the ipsilateral semicircular canals of the labyrinth, are particularly revealing in this respect. They suggest that, compared with the few other Laurasian titanosaurs for which in-depth palaeoneurological data are available, the French taxon is more derived than the distinctly more ancient, possibly non-lithostrotian titanosaur from the Uzbek site of Dzharakuduk but more basal than derived saltasaurids, such as the coeval or slightly more recent forms from the Spanish locality of Lo Hueco.