Rodolfo A. García

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.

A new titanosaur sauropod dinosaur from the Upper Cretaceous of North Patagonia, Argentina

A new sauropod titanosaur from the Upper Cretaceous Anacleto Formation is described. Narambuenatitan palomoi gen. et sp. nov., is diagnosed by cranial and axial autapomorphies. The holotype, which represent a subadult individual, consists of the left premaxilla and maxilla, braincase, both quadrates, one cervical vertebrae, one dorsal vertebra, fragments of cervical and dorsal ribs, seventeen caudal vertebrae, caudal transverse processes, fragments of haemal arches, left sternal plate, right coracoid, left humerus, left ulnae, both pubes, iliac pedicel, proximal fragment of right ischia, and an incomplete left femur. The phylogenetic analysis indicates that Narambuenatitan is a non-eutitanosaurian lithostrotian, and that it shares with Epachthosaurus a neural spine in middle caudal vertebrae which are laminar and posteriorly elongated.

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.

A Large Accumulation of Avian Eggs from the Late Cretaceous of Patagonia (Argentina) Reveals a Novel Nesting Strategy in Mesozoic Birds

We report the first evidence for a nesting colony of Mesozoic birds on Gondwana: a fossil accumulation in Late Cretaceous rocks mapped and collected from within the campus of the National University of Comahue, Neuquén City, Patagonia (Argentina). Here, Cretaceous ornithothoracine birds, almost certainly Enanthiornithes, nested in an arid, shallow basinal environment among sand dunes close to an ephemeral water-course. We mapped and collected 65 complete, near-complete, and broken eggs across an area of more than 55 m2. These eggs were laid either singly, or occasionally in pairs, onto a sandy substrate. All eggs were found apparently in, or close to, their original nest site; they all occur within the same bedding plane and may represent the product of a single nesting season or a short series of nesting attempts. Although there is no evidence for nesting structures, all but one of the Comahue eggs were half-buried upright in the sand with their pointed end downwards, a position that would have exposed the pole containing the air cell and precluded egg turning. This egg position is not seen in living birds, with the exception of the basal galliform megapodes who place their eggs within mounds of vegetation or burrows. This accumulation reveals a novel nesting behaviour in Mesozoic Aves that was perhaps shared with the non-avian and phylogenetically more basal troodontid theropods.

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.

The Titanosaur Sauropods from the Late Campanian—Early Maastrichtian Allen Formation of Salitral Moreno, Río Negro, Argentina

The dinosaur record of the Salitral Moreno locality (Río Negro Province, Argentina) is characterized by a high diversity of herbivore taxa, among them hadrosaurs, ankylosaurs, and titanosaur sauropods, but carnivores are rare, consisting of only a few fragmentary bones of small forms. Titanosaurs are represented by Rocasaurus muniozi and Aeolosaurus sp., and at least four other taxa, represented by fragmentary material. The elements preserved include a cervical, dorsal and caudal vertebrae, chevron, humerii, ulnae, radii, metacarpal, femora, tibiae, metatarsal, ischia, pubis, and ilium. The Allen Formation is thought to be correlated with the Marília Formation in Brazil, and their faunas have certain elements in common such as aeolosaurines, but saltasaurines and hadrosaurs, are known exclusively from the Allen Formation. These absences, and particularly that of the saltasaurines, may be because those sauropods originated late in the Cretaceous, probably in southern South America (Northern Patagonia?), and they did not have time to disperse to northern South America.

Considerations on the neural laminae of the sauropod dinosaurs and their morpho-functional meaning

Considerations on the neural laminae of the sauropod dinosaurs and their morpho-functional meaning. The axial skeleton of sauropod dinosaurs is distinguished by the presence of vertebral laminae that connect different points between the neural arch and the centrum. Previous exhaustive studies have conferred phylogenetic value to the array and organization of these structures. These studies among others, have also explored the function of the laminae. Many authors suggested that the characteristic cross-shaped transverse section of the sauropod dorsal neural spine (resulting of the axial prespinal and postspinal laminae, and the lateral structures formed by the fusion of the spinodiapophyseal and spinopostzygapophyseal laminae) is a function of four large pneumatic grooves. In this study, we associate the pattern of the sauropod (specially of the titanosaur) neural laminae with soft anatomy structures, such as aerial diverticula and interneural and other epaxial muscles; we consider surfaces and spaces bounded by these laminae, and how they vary in the dorsal sequence. The inferred musculature, specially the transversospinalis group, is based on myology of extant lepidosauriomorphs and archosauriomorphs.

Osteología embrionaria de saurópodos titanosaurios de Neuquén (Argentina): aspectos ontogenéticos y evolutivos

Abstract Embryonic osteology of titanosaur sauropods from Neuquén (Argentina): ontogenetic and evolutionary considerations. Titanosaur embryonic remains are described from megaloolithid eggs collected in the Anacleto Formation (Late Cretaceous) at Auca Mahuevo in Neuquén province (Argentina). These remains include complete articulate and disarticulate skulls, and numerous cranial and appendicular isolated elements. The embryonic skull is short, high, and presents numerous fenestrae, most of which are known in adult titanosaurs. However, the morphology of the maxilla and jugal is very different from that of adult titanosaurs. These elements show a series of processes that arise from their central body, which seem to have become reduced and transformed during ontogeny. The dental formula (Pm4 M7-8 /D10?) is similar to that of known adult titanosaurs. Detailed osteological study of these remains shows features of taxonomic, phylogenetic, and evolutionary significance. Several of the characters, including the snout with “stepped” anterior margin and the infratemporal fenestra extending ventrally to the orbit support the identification of the embryos as eusauropods. Other characters, such as the absence of crown denticles and the presence of a preantorbital fenestra are considered to be synapomorphies of Neosauropoda. Finally, the posteriorly wide skull and a maxillary notch at the ventral margin of the skull are regarded as synapomorphies of Titanosauria. Characters such as relatively large orbit, short rostral portion of the skull, long alveolar rows, “egg tooth”, tooth crowns lacking wear facets, frontal occupying practically the entire dorsal margin of the orbit, and nonossified postcranial axial skeleton are typical characters of sauropod embryonic and juvenile stages.

An “egg-tooth”–like structure in titanosaurian sauropod embryos

Remains of dinosaur embryos and neonates are extremely rare (Carpenter and Alf, 1994; Schweitzer et al., 2002; Varricchio et al., 2002; Deeming and Unwin, 2004; Reisz et al., 2005), a fact that historically has limited our knowledge on the ontogeny of these animals (Weishampel and Horner, 1994; Horner, 2000). For this reason, osteological evidence in relation to their probable hatching strategies is practically nil; the only inferences on this subject were made by Carpenter (1999) and Mueller-Töwe and colleagues (2002), but based on eggs portraying hatching windows, not specifically on embryos. Carpenter (op. cit.) supposed that “the dinosaur hatchling pushed its way out of the egg much like a megapode bird” (Carpenter, 1999:214), thus assuming that dinosaurs were deprived of a special hatching structure, like an egg-tooth. On the contrary, Mueller-Töwe and colleagues (op. cit.) stated that the (unknown) hatching embryos from spherical eggs form China (referred to the oogenus Megaloolithus), and Mongolia (Faveoloolithus), as well as those from elongated eggs assignable to theropods from China, would have had an egg-tooth, ‘caruncle,’ or a similar structure (MuellerTöwe et al., 2002). The goal of this communication is to announce the identification of an ‘egg-tooth’–like structure in exceptionally preserved sauropod embryos in ovo (tiny skeletons inside eggs of the oofamily Megaloolithidae of parataxonomic classification [Chiappe et al., 1998, 2000; Grellet-Tinner et al., 2004]), from the Upper Cretaceous of Patagonia (Argentina), which reinforces the previous belief of Mueller-Töwe and colleagues. Unlike those eggs studied by Carpenter (1999), Mueller-Töwe and colleagues (2002), and Cousin and colleagues (1994), the megaloolithids from Patagonia were not hatched, and therefore, their eggshells do not exhibit hatching windows (Grellet-Tinner et al., 2004). This new evidence sheds some light on the hatching strategies of sauropods, illuminating aspects of their ontogeny and evolution (García, in prep.). The specimens herein reported come from Auca Mahuevo (Neuquén Province, Argentina), and from the Anacleto Formation, the uppermost stratigraphic unit of the Neuquén Group (Ramos, 1981; Chiappe et al., 1998, 2000; Dingus et al., 2000) (Fig. 1), whose age has been estimated as Campanian (Dingus et al., 2000). In the area of study, the 85 m-thick sequence is composed predominantly of sandstones, siltstones and mudstones (Chiappe et al., 2000, 2004). Four egg-layers have been identified, but the embryos here and elsewhere described come all from the egg-layer 3 (Chiappe et al., 1998, 2000, 2001; Chiappe and Dingus, 2001; Chiappe and Coria, 2004; Salgado et al., 2005). Institutional Abbreviations—MCF-PVPH, Museo “Carmen Funes”—Paleontología de Vertebrados, Plaza Huincul; MPCA, Museo Provincial Carlos Ameghino, Cipolletti; PVL, Paleontología de Vertebrados, Instituto Lillo, Tucumán. MORPHOLOGY OF THE EMBRYONIC PREMAXILLAE

Morphology, Microanatomy, and Histology of Titanosaur (Dinosauria, Sauropoda) Osteoderms from the Upper Cretaceous of Patagonia

ABSTRACT Titanosaurs are the only group of sauropodomorph dinosaurs that possesses osteoderms. The Anacleto and Allen formations (Upper Cretaceous) from northern Patagonia (Argentina) have provided an abundance of these elements, isolated or associated with more or less complete skeletons. Here, we study the morphology, microanatomy, and histology of titanosaur osteoderms found in these stratigraphic units. The size and gross anatomy of the osteoderms are strongly variable, as well as their microanatomy, which ranges from compact structures to those with strong development of cancellous bone. The primary bone tissue is composed of structural fiber bundles that are ossified by dermal metaplasia. Bone pathologies were identified in at least two osteoderms. Bone histology suggests that the osteoderms were entirely imbedded in the stratum compactum of the dermis. Titanosaur osteoderms were probably employed for multiple functions, including mineral storage and defense.