Ignacio A. Cerda

The Osteology of Chubutisaurus insignis Del Corro, 1975 (Dinosauria: Neosauropoda) from the ‘Middle’ Cretaceous of Central Patagonia, Argentina

ABSTRACT Titanosauriform sauropods were one of the most widely distributed groups of dinosaurs during the Cretaceous. In contrast to most derived forms from the Upper Cretaceous, the most basal taxa of the group are poorly known. Thus, studies on these forms are of special interest for understanding the origin and early evolution of Titanosauria. Chubutisaurus insignis del Corro, 1975, is known from postcranial remains found in the Bayo Overo Member of the Cerro Barcino Formation (Chubut Group), which is commonly regarded as Aptian—Cenomanian in age. Phylogenetic analyses that include Chubutisaurus recovered this taxon as the sister group to Titanosauria. Nevertheless, most published studies have not included this taxon, probably due to its brief description and fragmentary remains. Fieldwork conducted in the quarry where the holotype was found yielded new materials that are regarded as part of the same specimen. These new materials, together with additional undescribed, and briefly described elements, originally collected by G. del Corro, are described here. The new information allows the recognition of a more extensive diagnosis of this taxon. The phylogenetic analysis presented here resolves Chubutisaurus as the most basal somphospondylian.

A New Sauropodomorph Dinosaur from the Early Jurassic of Patagonia and the Origin and Evolution of the Sauropod-type Sacrum

Background The origin of sauropod dinosaurs is one of the major landmarks of dinosaur evolution but is still poorly understood. This drastic transformation involved major skeletal modifications, including a shift from the small and gracile condition of primitive sauropodomorphs to the gigantic and quadrupedal condition of sauropods. Recent findings in the Late Triassic–Early Jurassic of Gondwana provide critical evidence to understand the origin and early evolution of sauropods. Methodology/Principal Findings A new sauropodomorph dinosaur, Leonerasaurus taquetrensis gen. et sp. nov., is described from the Las Leoneras Formation of Central Patagonia (Argentina). The new taxon is diagnosed by the presence of anterior unserrated teeth with a low spoon-shaped crown, amphicoelous and acamerate vertebral centra, four sacral vertebrae, and humeral deltopectoral crest low and medially deflected along its distal half. The phylogenetic analysis depicts Leonerasaurus as one of the closest outgroups of Sauropoda, being the sister taxon of a clade of large bodied taxa composed of Melanorosaurus and Sauropoda. Conclusions/Significance The dental and postcranial anatomy of Leonerasaurus supports its close affinities with basal sauropods. Despite the small size and plesiomorphic skeletal anatomy of Leonerasaurus, the four vertebrae that compose its sacrum resemble that of the large-bodied primitive sauropods. This shows that the appearance of the sauropod-type of sacrum predated the marked increase in body size that characterizes the origins of sauropods, rejecting a causal explanation and evolutionary linkage between this sacral configuration and body size. Alternative phylogenetic placements of Leonerasaurus as a basal anchisaurian imply a convergent acquisition of the sauropod-type sacrum in the new small-bodied taxon, also rejecting an evolutionary dependence of sacral configuration and body size in sauropodomorphs. This and other recent discoveries are showing that the characteristic sauropod body plan evolved gradually, with a step-wise pattern of character appearance.

A new sauropod titanosaur from the Plottier Formation (Upper Cretaceous) of Patagonia (Argentina)

This paper presents a new titanosaur sauropod, collected from levels of reddish clays assigned to the Plottier Formation (Coniacian-Santonian). The holotype of Petrobrasaurus puestohernandezi gen. et. sp. nov. is a disarticulated specimen, from which teeth, cervical, dorsal and caudal vertebrae, sternal plates, metacarpals, femora, tibia, a fragment of ilium, pubis, haemal arches, and cervical and dorsal ribs have been preserved. This period is of particular interest because it saw the definitive isolation of the vertebrate faunas of Patagonia, with the separation of South America from the rest of Gondwana, a process that had begun during the Early Cretaceous. Although some of the characters observed in Petrobrasaurus gen. nov. suggest a relationship with the South American clade Lognkosauria, this new sauropod is regarded as Titanosauria incertae sedis until a more profound analysis of the Titanosauria that in which it is included is undertaken.

Extreme postcranial pneumaticity in sauropod dinosaurs from South America

Birds are unique among living tetrapods in possessing pneumaticity of the postcranial skeleton, with invasion of bone by the lung and air-sac system. Postcranial skeletal pneumaticity (PSP) has been reported in numerous extinct archosaurs including pterosaurs and non-avian dinosaurs. Here we report a case of extreme PSP in a group of small-bodied, armored sauropod dinosaurs from the Upper Cretaceous of South America. Based on osteological data, we report an extensive invasion of pneumatic diverticula along the vertebral column, reaching the distal portion of the tail. Also, we provide evidence of pneumaticity in both pectoral and pelvic girdles. Our study reveals that the extreme PSP in archosaurs is not restricted to pterosaurs and theropod dinosaurs.KurzfassungVögel sind einzigartig innerhalb der lebenden Tetrapoden, da sie eine Pneumatisierung des Postkranialskeletts aufweisen, welche die Invasion von Knochen durch die Lunge und Luftsack-Systeme einschließt. Diese postkraniale Skelettpneumatisierung (PSP) ist bereits in zahlreichen ausgestorbenen Archosauriern, einschließlich Pterosauriern und Dinosauriern, die nicht der Vogellinie angehören, beschrieben worden. Hier berichten wir über einen Fall von extremer PSP in einer Gruppe von kleinwüchsigen, gepanzerten sauropoden Dinosauriern aus der Oberkreide von Südamerika. Basierend auf osteologischen Daten lässt sich eine umfangreiche Invasion von pneumatischen Divertikeln entlang der Wirbelsäule nachweisen, welche sich bis in die distalen Bereiche des Schwanzes erstreckt. Darüber hinaus zeigen sich Hinweise auf Pneumatisierung in beiden Brust- und Beckengürteln. Unsere Studie zeigt, dass diese extreme Form von PSP in Archosauriern nicht auf Flugsaurier und theropode Dinosaurier beschränkt ist.

The first record of a sauropod dinosaur from Antarctica

Sauropoda is one of the most diverse and geographically widespread clades of herbivorous dinosaurs, and until now, their remains have now been recovered from all continental landmasses except Antarctica. We report the first record of a sauropod dinosaur from Antarctica, represented by an incomplete caudal vertebra from the Late Cretaceous of James Ross Island. The size and morphology of the specimen allows its identification as a lithostrotian titanosaur. Our finding indicates that advanced titanosaurs achieved a global distribution at least by the Late Cretaceous.

Dermal armor histology of Saltasaurus loricatus, an Upper Cretaceous sauropod dinosaur from Northwest Argentina

The first unambiguous evidence of the presence of osteoderms in sauropod dinosaurs came from the discovery of Saltasaurus loricatus, a titanosaur from the Upper Cretaceous of Argentina. The dermal armor of Saltasaurus is composed of bony plates and small dermal ossicles. Here, we analyze the bone microstructure of these elements and provide information regarding its origin and development. The bony plates are composed almost entirely of reconstructed cancellous bone. Remains of primary bone consist of coarse bundles of mineralized collagenous fibers towards the external surface. Also, woven fibered bone tissue appears in the basal and lateral regions. Dermal ossicles lack secondary remodeling, and their matrix is formed by three orthogonal systems of collagenous fiber bundles. Growth lines are present in both bony plates and ossicles. Bone histology reveals that osteoderms mainly originated through direct mineralization (metaplasia) of the dermis, although other mechanisms are also involved (at least in the origin of dermal plates). The common features of development and integumental location of the osteoderms of Saltasaurus and other non-related vertebrates (e.g., lepidosaurs, crocodylomorphs) are linked to the intrinsic skeletogenic properties of the dermis.

Paleobiology of Titanosaurs: Reproduction, Development, Histology, Pneumaticity, Locomotion and Neuroanatomy from the South American Fossil Record

Abstract. Much of the current paleobiological knowledge on titanosaur sauropods was attained in just the last fifteen years, in particular that related to reproductive and developmental biology. Recent years have also seen progress on other poorly explored topics, such as pneumaticity, muscle architecture and locomotion, and endocast reconstruction and associated structures. Some titanosaurs laid numerous, relatively small Megaloolithidae eggs (with diameters ranging from 12 to 14 cm) in nests dug In the ground and, as known from the South American records, probably eggs of the multispherulitic morphotype. During ontogeny, certain titanosaurs displayed some variations in cranial morphology, some of them likely associated with the differing feeding habits between hatchlings and adults. The bone tissue of some adult titanosaurs was rapidly and cyclically deposited and shows a greater degree of remodeling than in other sauropods. Saltasaurines in particular show evidence of postcranial skeletal pneumaticity in both axial and appendicular skeleton, providing clues about soft tissue anatomy and the structure of the respiratory system. Titanosaurs, like all sauropods, were characterized by being fully quadrupedal, although some appendicular features and putative trackways indicate that their stance was not as columnar as in other sauropods. These anatomical peculiarities are significantly developed In saltasaurines, a derived group of titanosaurs. Compared with other sauropods, some titanosaurs seem to have had very poor olfaction but would have been capable of capturing sounds In a relatively wide range of high frequencies, although not to the extent of living birds.

Bone Histology of Phytosaur, Aetosaur, and Other Archosauriform Osteoderms (Eureptilia, Archosauromorpha)

As in other archosauriforms, phytosaurs and aetosaurs are characterized by the presence of well‐developed osteoderms. Here we provide a comparative study on the microstructure of phytosaur (five taxa) and aetosaur (thirteen taxa) osteoderms. For outgroup comparison, we sampled osteoderms of the sister taxon to Aetosauria, Revueltosaurus callenderi, and the doswelliid Jaxtasuchus salomoni. Phytosaur, aetosaur, and Jaxtasuchus osteoderms are composed of a diploe structure, whereas the Revueltosaurus osteoderm microanatomy is more compact. The external cortex of phytosaurs, Revueltosaurus and Jaxtasuchus osteoderms is mainly composed of parallel‐fibered bone. In aetosaurs, the external cortex mainly consists of lamellar bone, with lines of resorption within the primary bone indicating successive cycles of bone erosion and deposition. The basal cortex in all the specimens is composed of parallel‐fibered bone, with the cancellous internal core being more strongly developed in aetosaurs than in phytosaurs. Woven or fibro‐lamellar bone was recorded in both phytosaurian and aetosaurian taxa, as well as in Jaxtasuchus. Structural fibers, which at least partly suggest metaplastic origin, were only recorded in the internal core of two phytosaurs and in the basal cortex of one aetosaur. Osteoderm thickness and cancellous to compact bone ratios appear to be subject to ontogenetic change. Minimum growth mark counts in osteoderms sampled indicate that some aetosaurs and phytosaurs lived for at least two decades. Bone microstructures are more uniform in phytosaur osteoderms and show a higher level of disparity among aetosaur osteoderms, and at least in the latter, histological features are potentially apomorphic for species/genus level. Anat Rec, 297:240–260, 2014.

Biological Implications of the Bone Microstructure of the Late Cretaceous Ornithopod Dinosaur Gasparinisaura cincosaltensis

ABSTRACT Here we present the bone histology of Gasparinisaura cincosaltensis, a basal ornithopod from the Late Cretaceous of Patagonia, and discuss its biological implications. The sample includes axial and appendicular elements from several specimens of different ontogenetic stages. The cortex of most bones consists of fibro-lamellar tissue, with mainly longitudinally oriented vascular spaces, which suggests rapid osteogenesis and fast growth. However, the fibro-lamellar bone is commonly interrupted by lines of arrested growth and/or annuli composed of parallel-fibered bone that indicates that the rapid growth was periodic. Although a true outer circumferential layer was not recorded in any of the sampled elements, in several of the larger samples the woven-fibered matrix of the inner and middle cortex grades into a parallel-fibered tissue, which suggests that the attainment of sexual maturity occurred before skeletal maturity. The growth dynamics of Gasparinisaura are similar to those reported in other basal ornithopods. Inter-elemental, as well as intraspecific, variations in histology were observed in Gasparinisaura. Such variation could be the result of sexual dimorphism, or the effect of localized conditions of growth, or perhaps plasticity in growth in response to local environmental conditions.

Dentición de titanosaurios (Dinosauria, Sauropoda) del Cretácico Superior de la provincia de Río Negro, Argentina: morfología, inserción y reemplazo

Abstract Dentition of titanosaurs (Dinosauria, Sauropoda) from the Upper Cretaceous of Río Negro Province, Argentina: morphology, implantation and replacement. A fragment of dentary of a titanosaur sauropod from the Anacleto Formation (Upper Cretaceous of the Río Negro Province) is described. Inside the alveoli, functional and replacement teeth in successive “premature” stages are observed. At least in the preserved portion, an alternate teeth replacement pattern is observed. The histological analysis of this specimen allowed identifying the attachment dental tissues (alveolar bone, cementum and periodontal ligament). Numerous isolated teeth from the same unit and from the overlying Allen Formation are described. Based on these, a classification of the wear facets is proposed: 1) Teeth with only one facet: on the labial side, on the lingual side, or on the lateral side. 2) Teeth with two facets: the bigger on the labial side and the smaller on the lingual side; the bigger on the lingual side and the smaller on the labial side; the bigger on the lingual side and the smaller on the mesial or distal edge. 3) Teeth with three facets: one on the lingual side, the others on the mesial and distal edges; one on the lingual side, the others on the labial and mesial or distal edges; one on the labial side, the others on the mesial and distal edges. 4) Teeth with four facets: the smaller on the labial side, the bigger on the lingual side, and two lateral facets, one on the mesial and the other on the distal edges. Finally, we propose a hypothesis about the origin of the wear facets.