Lucas E. Fiorelli

The oldest known communal latrines provide evidence of gregarism in Triassic megaherbivores

Defecation in communal latrines is a common behaviour of extant mammals widely distributed among megaherbivores. This behaviour has key social functions with important biological and ecological implications. Herbivore communal latrines are only documented among mammals and their fossil record is exceptionally restricted to the late Cenozoic. Here we report the discovery of several massive coprolite associations in the Middle-Late Triassic of the Chañares Formation, Argentina, which represent fossil communal latrines based on a high areal density, small areal extension and taphonomic attributes. Several lines of evidence (size, morphology, abundance and coprofabrics) and their association with kannemeyeriiform dicynodonts indicate that these large synapsids produced the communal latrines and had a gregarious behaviour comparable to that of extant megaherbivores. This is the first evidence of megaherbivore communal latrines in non-mammal vertebrates, indicating that this mammal-type behaviour was present in distant relatives of mammals, and predates its previous oldest record by 220 Mya.

A new Argentinean nesting site showing neosauropod dinosaur reproduction in a Cretaceous hydrothermal environment

Although several late Cretaceous sauropod colonial nesting sites have been discovered nearly on every continent during the last few decades, no studies have been performed to determine the factors that underpinned the choice of these specific sites. Here, we report the first definitive evidence of a group of sauropods that nested repetitively and purposely at a Cretaceous hydrothermal site at Sanagasta, La Rioja Province, Argentina. The discovery of this new colonial nesting locality shows nest fidelity over a long time, and a symbiotic relationship between egg clutches and a peculiar hydrothermal environment that favoured their incubation. Sedimentary and geochemical analyses of 80 clutches and their large eggs with thick eggshells substantiate that the Sanagasta sauropods were specifically using the soil moisture and thermoradiance to incubate their eggs, similar to a few extant species, namely, the megapode, Megapodius pritchardii, which is known to lay its egg clutches in burrows at volcanically heated nesting grounds.

Water Vapor Conductance of the Lower Cretaceous Dinosaurian Eggs from Sanagasta, La Rioja, Argentina: Paleobiological and Paleoecological Implications for South American Faveoloolithid and Megaloolithid Eggs

ABSTRACT The water vapor conductance (GH2O) of the neosauropod eggs from the Lower Cretaceous Sanagasta nesting site in La Rioja Province, Argentina, was examined and compared with other Cretaceous Argentinean oological material. The 2900 mgH2O/day·Torr GH2O of the Sanagasta eggshells confirms an extremely moist nesting environment and supports field observations of dug-out nests in a geothermal setting. The observed thinning of the outer eggshell surface during incubation increases gas conductance and concomitantly decreases eggshell mechanical resistance during the late ontogenetic stages, thus facilitating embryonic development and hatching. The Sanagasta and Entre Ríos Province faveoloolithid eggs display the highest and comparable GH2O values and share several morphological and diagenetic characters, indicating comparable nesting strategy in geothermal settings. However, the faveoloolithid Yaminué and La Pampa Province specimens cluster together with lower GH2O values closer to the megaloolithid eggs. The GH2O of the megaloolithid egg Megaloolithus patagonicus was reconsidered and new results are now congruent with other reported megaloolithid GH2O values. Additionally, we hypothesize that Y-shaped pore canals of M. patagonicus, which upper sections reach only the top third or half eggshell thickness and, a wider section in the middle would not compromise the overall egg mechanical resistance like vertical pores connecting directly the outer to the inner eggshell surfaces. Such pore spatial arrangement and geometry would enhance, as the eggshell thins during incubation, a greater GH2O, GO2 and GCO2 and facilitate embryonic development in high moisture nesting contents. Overall, data suggests that neosauropod nesting and brooding behaviors were dependent on elevated moisture nesting environments.

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.

The oldest rhynchosaur from Argentina: a Middle Triassic rhynchosaurid from the Chanares Formation (Ischigualasto-Villa Union Basin, La Rioja Province)

Rhynchosaurs first appear in the Early Triassic fossil record and flourished during the late Carnian as the dominant members of several assemblages worldwide. In Argentina, the rhynchosaur record is currently restricted to the Ischigualasto Formation of late Carnian–earliest Norian age. Recent fieldwork in the new locality of Brazo del Puma, in the lowermost levels of the Chañares Formation, yielded three rhynchosaur tooth-bearing bones, which were collected five metres above the contact with the underlying Tarjados Formation. The most complete specimen is the posterior end of the alveolar region of a left dentary. The dentary possesses densely packed tooth rows on the lingual surface and medial half of the occlusal surface, showing longitudinal Zahnreihen. The teeth of the occlusal surface are worn flat and those of the lingual surface are organized in multiple rows, supporting the referral of the specimen to Rhynchosauridae. In addition, the dentary teeth are conical to mesiodistally compressed, resembling the condition observed in hyperodapedontines. The rhynchosaur remains reported here are the oldest collected in Argentina and among the oldest in South America, together with an unnamed form from Brazil. The new rhynchosaur specimens come from levels in which dicynodonts are numerically dominant, whereas cynodonts are considerably less abundant. Accordingly, the specimens reported here bolster faunal differences within the Chañares Formation and add a new faunal component to this already diverse vertebrate assemblage.KurzfassungRhynchosaurier sind erstmals für die Untere Trias im Fossilbericht nachgewiesen und erlebten ihre Blüte im Oberen Karnium, als eine dominierende Gruppe in merheren Fossilgesellschaften weltweit. In Argentinien sind Rhynchosauier bislang nur für die Ischigualasto Formation (Oberes Karnium-Unteres Norium) belegt. Kürzliche Grabungen in einer neuen Lokalität in Brazo del Puma, im unteresten Niveau der Chañares Formation, ergaben drei zahntragende Knochen von Rhynchosaurierern. Die Knochen wurden ungefähr fünf Meter über unterliegenden Tarjados Formation gefunden. Der vollständigste Knochen repräsentiert das posteriore Ende der Zahnregion in der linken Dentale. Die Dentale besitzt dichtgepackte Zahnreihen auf der lingualen Seite und längslaufenden Zahnreihen auf der medialen Hälfte der okklusalen Seite. Die abgeflachten Zähne der okklusalen Seite sowie die mehrreihige Anordnung der Zähne auf der lingualen Seite erlaubt eine Zuordnung zu den Rhynchosauriden. Die Zähne der Dentalen sind zusätzlich konisch bis mesiodistad zusammengedrückt, ähnlich den Zähnen von Hyperodapedontinen. Zusammen mit unbeschriebenen Resten aus Brasilien, repräsentieren die hier vorgestellten Reste den ältesten Nachweis von Rhynchosauriern aus Argentinien beziehungsweise Südamerika. Die Rhynchosaurierknochen stammen aus einem Niveau, dass vor allem durch Dicynodonten dominiert ist, während Cynodonten seltener vorkommen. Die hier vorgelstellten Reste erweitern daher die bekannte Fauna der Chañares Formation um eine weitere Gruppe und belegen zusätzlich zeitliche Unterschiede in der Faunenzusammensetzung innerhalb der Formation.

Deep faunistic turnovers preceded the rise of dinosaurs in southwestern Pangaea

The Triassic period documents the origin and diversification of modern amniote lineages and the Late Triassic fossil record of South America has been crucial to shed light on these early evolutionary histories. However, the faunistic changes that led to the establishment of Late Triassic ecosystems are largely ignored because of the global scarcity of fossils from assemblages a few million years older. Here we contribute to fill this gap with the description of a new tetrapod assemblage from the lowermost levels of the Chañares Formation (uppermost Middle–lower Late Triassic epochs) of Argentina, which is older than the other vertebrate assemblages of the same basin. The new assemblage is composed of therapsids, rhynchosaurids and archosaurs, and clearly differs from that of the immediately overlying and well-known historical Chañares vertebrate assemblage. The new tetrapod association is part of a phase of relatively rapidly changing vertebrate assemblage compositions, in a time span shorter than 6 million years, before the diversification of dinosaurs and other common Late Triassic tetrapods in southwestern Pangaea.A Middle–Late Triassic tetrapod assemblage from South America reveals a series of faunal turnovers prior to the rise of dinosaurs in the region.

What do giant titanosaur dinosaurs and modern Australasian megapodes have in common

Titanosauria is a globally distributed clade of sometimes extremely large Mesozoic herbivorous sauropod dinosaurs. On the basis of current evidence these giant dinosaurs seem to have reproduced in specific and localized nesting sites. However, no investigations have been performed to understand the possible ecological and geological biases that acted for the selection of these nesting sites worldwide. In this study, observations were performed on the best-known Cretaceous nesting sites around the world. Our observations strongly suggest their eggs were incubated with environmental sources of heat, in burial conditions. Taking into account the clutch composition and geometry, the nature and properties of the sediments, the eggshells’ structures and conductance, it would appear that titanosaurs adopted nesting behaviors comparable to the modern Australasian megapodes, using burrow-nesting in diverse media and mound-building strategies.

Tafonomía del Sitio de Nidificación de Neosaurópodos de Sanagasta (la Rioja, Argentina): Ejemplo de Preservación Excepcional en un Paleoambiente Hidrotermal del Cretácico

Abstract. TAPHONOMY OF THE NEOSAUROPOD NESTING SITE FROM SANAGASTA (LA RIOJA, ARGENTINA): EXCEPTIONAL PRESERVATION IN A CRETACEOUS HYDROTHERMAL PALEOENVIRONMENT. The Cretaceous Sanagasta nesting site, La Rioja Province, Argentina, has shed insights on the reproductive behavior of neosauropods, documenting colonial behavior, phylopatry, and an opportunistic environment-dependent-reproduction relationship with their paleoenvironment. The taphonomy of this monotypic nesting site is described in order to assess its biostratinomy and fossil diagenesis. The 3D spatial egg-clutch arrangement is well preserved and suggests the presence of autochthonous associations with in-situ ovipositions, without nesting trace. The egg-bearing level presents a matrix-supported packed biofabric and an “intrinsic” biogenic accumulation that implies a gregarious behavior through their preferential colonization of a specific paleohydrothermal nesting site. The biocenosis of biogenically deposited eggs, with eggshell mineralization is altered by hydrothermal activity, and extremophile microorganisms. The thanatocenosis and time-averaging were virtually null because the eggs buried in the substrate immediately after being laid. In contrast, the taphocenosis represents the most important taphonomic feature. The eggshells display several synchronous taphonomic alterations produced by acidic hot spring solutions, while re-calcification and silicification are the most common eggshell recrystallizations. The presence of microchert, chalcedony, ∼10 μm-diamteer opal-A microspheres, epidote aggregates, several macro-structures, and fibrous clay minerals replacing parts of the eggshell and egg membranes, indicates an extreme hydrothermal alteration under exceptional conditions. The presence of fossil stromatolites, cyanobacterians, and diatoms, coupled with sedimentary structures (microfacies and hydrothermal microfabrics), and with eggs taphonomy imply that the Sanagasta nesting site represents a particular instance of taphocenosis and a Lagerstätte. The Sanagasta dinosaur nesting site is the first documented case of environment-dependent reproduction amongst neosauropods.

Micro-CT scan reveals an unexpected high-volume and interconnected pore network in a Cretaceous Sanagasta dinosaur eggshell

The Cretaceous Sanagasta neosauropod nesting site (La Rioja, Argentina) was the first confirmed instance of extinct dinosaurs using geothermal-generated heat to incubate their eggs. The nesting strategy and hydrothermal activities at this site led to the conclusion that the surprisingly 7 mm thick-shelled eggs were adapted to harsh hydrothermal microenvironments. We used micro-CT scans in this study to obtain the first three-dimensional microcharacterization of these eggshells. Micro-CT-based analyses provide a robust assessment of gas conductance in fossil dinosaur eggshells with complex pore canal systems, allowing calculation, for the first time, of the shell conductance through its thickness. This novel approach suggests that the shell conductance could have risen during incubation to seven times more than previously estimated as the eggshell erodes. In addition, micro-CT observations reveal that the constant widening and branching of pore canals form a complex funnel-like pore canal system. Furthermore, the high density of pore canals and the presence of a lateral canal network in the shell reduce the risks of pore obstruction during the extended incubation of these eggs in a relatively highly humid and muddy nesting environment.