Mariela Soledad Fernández

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.

Parataxonomic review of the Upper Cretaceous dinosaur eggshells belonging to the oofamily Megaloolithidae from India and Argentina

The eggshell oospecies from India and Argentina are compared and reviewed in detail. These eggshells resemble each other in having a nodular outer surface ornamentation and clearly arched growth lines of the shell units. Microstructurally, the eggshell oospecies belonging to the oofamily Megaloolithidae shows fan-like shell units, which are sharply separated from each other throughout the thickness of the eggshell and can be traced up to the surface of the eggshell. Comparisons between four oospecies from India and Argentina reveal three groupings, which show similarities between megaloolithids of both countries: (1) Megaloolithus jabalpurensis, M. matleyi and M. patagonicus; (2) M. cylindricus, M. rahioliensis and Tipo 1d; and (3) M.megadermus and Tipo 1e. The other two types of eggshell oospecies from India and Argentina show partially fused external nodes and shell units. As a result, growth lines enter into the adjacent shell units with a marked concavity. A new oogenus Fusioolithus have been erected due to fusion between shell units and tubospherulitic morphotype, which include two new oospecies F. baghensis and F. berthei. Till date, morphostructurally, a total of 15 eggshell oospecies belonging to different oofamilies have been recorded from India and seven oospecies from Argentina.

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.

Análisis de Cáscaras de Huevos de Dinosaurios de La Formación Allen, Cretácico Superior de Río Negro (Campaniano-Maastrichtiano): Utilidad de Los Macrocaracteres de Interés Parataxonómico

Abstract. ANALYSIS OF DINOSAUR EGGSSHELLS OF ALLEN FORMATION, UPPER CRETACEOUS OF THE RIO NEGRO PROVINCE (CAMPANIAN-MAASTRICHTIAN) : USEFULNESS OF MACRO CHARACTERS OF PARATAXONOMIC INTEREST. The present study is a further contribution to the parataxonomy knowledge of dinosaur eggshells from Salitral de Santa Rosa and Salitral Ojo de Agua, Río Negro province, Argentina. We studied 4469 fragments of dinosaur eggshells Allen Formation, Upper Cretaceous (Campanian-Maastrichtian). Twelve of these shells were subject to a principal component analysis (PCA) to classify and establish the relationships between characters commonly used in parataxonomic classifications. We studied under binocular scope 4264 eggshells (BL), 57 eggshells under transmitted light microscope (TLM) and polarized light microscope (PLM), 14 eggshells under scanning electron microscope (SEM). We identified two main groups, type 1 eggshells related to the oofamily Megaloolithidae with five subtypes and type 2 eggshells, with no subtypes assigned. Relevant traits found with the ACP study were: shell thickness, the width of the shell units, the diameter of the nodules, and the diameter of the mamila. Different types of eggshells found were compared with various ootaxa from South America and other regions of the world.

The youngest egg of avian affinities from the Cretaceous of Patagonia

ABSTRACT We report the youngest fossil egg of avian affinities from the Cretaceous (Allen Formation, Campanian-Maastrichtian) of Patagonia, Argentina. The fossil consists in most of the internal cast of a single egg, preserving some eggshell fragments on one of its poles. Its axes are 4.5 cm and 3.06 cm. The eggshell surface is smooth, and its thickness average is 400 µm. The eggshell has two layers, with an ornithoid basic type and a ratite morphotype. The well-developed mammillary layer is 154 µm thick, with petal-shaped mammillae, the continuous layer is 251 µm thick. Shell microstructure is consistent with Laevisoolithidae, an ootaxon traditionally associated with enantiornithid birds. The shape of fibers of the testaceous membrane (TM) is preserved; these are flattened, with a thickness of 1.1 µm and a width of 4.8 µm each. The arrangement of the fibers of the TM is random, similar to that observed in extant reptiles. EDAX analysis reported that fibers are enriched in traces of Mg, Al, Si, P, F, and K, elements that are also present in both extant and fossil shell membrane. Cladistic analysis performed is consistent with the avian affinities established on the basis of macro, micro and ultrastructural characteristics.