Sea surface temperature contributes to marine crocodylomorph evolution

During the Mesozoic and Cenozoic, four distinct crocodylomorph lineages colonized the marine environment. They were conspicuously absent from high latitudes, which in the Mesozoic were occupied by warm-blooded ichthyosaurs and plesiosaurs. Despite a relatively well-constrained stratigraphic distribution, the varying diversities of marine crocodylomorphs are poorly understood, because their extinctions neither coincided with any major biological crises nor with the advent of potential competitors. Here we test the potential link between their evolutionary history in terms of taxic diversity and two abiotic factors, sea level variations and sea surface temperatures (SST). Excluding Metriorhynchoidea, which may have had a peculiar ecology, significant correlations obtained between generic diversity and estimated Tethyan SST suggest that water temperature was a driver of marine crocodylomorph diversity. Being most probably ectothermic reptiles, these lineages colonized the marine realm and diversified during warm periods, then declined or became extinct during cold intervals

Dinosaur Fossils Predict Body Temperatures

Perhaps the greatest mystery surrounding dinosaurs concerns whether they were endotherms, ectotherms, or some unique intermediate form. Here we present a model that yields estimates of dinosaur body temperature based on ontogenetic growth trajectories obtained from fossil bones. The model predicts that dinosaur body temperatures increased with body mass from approximately 25 °C at 12 kg to approximately 41 °C at 13,000 kg. The model also successfully predicts observed increases in body temperature with body mass for extant crocodiles. These results provide direct evidence that dinosaurs were reptiles that exhibited inertial homeothermy

Mineral magnetic characterization of the Upper Pleniglacial Nussloch loess sequence (Germany): an insight into local environmental processes

Presently, most loess/palaeosol magnetic susceptibility records are interpreted as following either the wind-vigour model or the pedogenic enhancement model. However redoxomorphic processes induced by waterlogging, often referred to gleying in the loess literature, are also known to alter loess deposits but their impact on loess/palaeosol magnetic susceptibility records has received little attention. The reported rock magnetic study aims to characterize the mineral magnetic response of loess to waterlogging-induced redoxomorphic processes, thus improving our understanding of mineral magnetic changes within loess deposits with respect to environmental and climate conditions. The Nussloch loess-palaeosol deposit (Rhine Valley, Germany) was targeted because it is one of the best-studied Pleniglacial deposits for Western Europe in which numerous tundra gley intervals have been identified. Moreover, a comprehensive high-resolution environmental magnetism study has never been undertaken for this site. Various rock magnetism experiments were conducted at both room and low temperatures to characterise the composition, concentration and relative magnetic grain size of the mineral magnetic assemblage. The relative changes in magnetic parameters within the investigated loess interval are primarily controlled by (1) varying concentrations of coarse-grained ferrimagnetic particles of detrital (aeolian) origin and (2) dissolution of fine-grained ferrimagnetic particles related to in situ post-depositional alteration promoted by waterlogging-induced redoxomorphic processes. Goethite is found to be ubiquitous throughout the studied interval and is argued to have both a primary (aeolian) and secondary (in situ) origin. We conclude, that redoxomorphic processes induced by waterlogging, if present, will hinder the interpretation of magnetic susceptibility variations within loess and palaeosol deposits following the expected relationships dictated by the wind-vigour and the pedogenic enhancement magnetism models

Multi-isotopic analysis reveals the early stem turtle Odontochelys as a nearshore herbivorous forager

IntroductionAfter decades of debate on the origin of turtles, it is now widely accepted that they are diapsid reptiles originating in the Permian from a terrestrial ancestor. It seems that the initial development of the structures that will later form the unique turtle bony shell took place as a response to a fossorial lifestyle. However, the earliest stem turtle with a fully complete plastron, Odontochelys semitestacea from the Late Triassic (lower Carnian) of China, is somewhat controversially interpreted as an aquatic or even a marine form, raising the question of the environment in which the completion of the plastron happened.MethodsHere, we analyzed the stable carbon, oxygen and sulfur isotope compositions (δ13C, δ18O and δ34S) of bones from two specimens of Odontochelys along with bones and teeth of two associated specimens of the marine ichthyosaur Guizhouichthyosaurus tangae.Results and discussionWe first show that δ18O values of Odontochelys are incompatible with a terrestrial lifestyle and imply a semi-aquatic to aquatic lifestyle. Isotopic results also demonstrate that the aquatic environment of Odontochelys was submitted to a strong marine influence, therefore excluding the possibility of a strict freshwater aquatic environment. Additionally, an unusual carbon isotope composition shows that O. semitestacea was herbivorous, probably consuming macrophytic algae in coastal zones like the extant green sea turtle (Chelonia mydas) or the marine iguana (Amblyrhynchus cristatus) do

Climate and Diet Evolution During Ancient Egypt

The Egyptian civilization arose and developed during the Predynastic period (7300 to 5000 years before present or BP e.g. before 1950), synchronous with a large scale climatic event, the end of the African Humid Period. The decrease in the amount of precipitation associated with this climate change could have started earlier in Ethiopia (maybe as soon as 8000 BP), while other regions of tropical and subtropical Africa were affected between 6000 and 5000 BP. Several sources point to a maximum of aridity around 5200 BP. This event could have contributed to the concentration of population inside the Nile valley, and thus to the rise of the Egyptian civilization. After this event, the climate became generally arid but unstable, switching between aridity peaks (in particular at 4000 BP) and relative wetter conditions. Lastly, after 1500 BP, the amount of rainfall became very low but steady. Consequently, the climatic fluctuations could also have affected Egypt during the dynastic period (5000 to 2000 BP). Here, oxygen isotope composition (delta O-18 value) of phosphate was measured in bone and enamel of Egyptian mummies in order to track climate evolution between 5500 and 1500 BP. The delta O-18 values of mineralized tissues reflect the isotopic composition of the drinking water of studied individuals, i.e. the water from the Nile River for Egyptians. Estimated delta O-18 values of the past Nile river water increased at the end of the studied period. This marks a decrease in the amount of precipitation or an increase in local temperatures at the two source regions of the river, namely Ethiopia and the Equatorial Lake Plateau. These results confirm that the drying trend continued during the dynastic period and question its effect on the Egyptian prosperity

Evolution du climat et du régime alimentaire pendant l’Egypte ancienne

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[delta]18 O de l'apatite de vertébrés continentaux du Crétacé (implications paléoclimatiques et thermophysiologiques)

Ce travail s inscrit dans l optique globale de recherche et d établissement d un indicateur paléoclimatique terrestre pour le Mésozoïque à partir de l enregistrement isotopique des faunes de reptiles. L étude proprement dite s est concentrée exclusivement sur l isolation des signaux thermométriques enregistrés dans la composition isotopique de l oxygène (18O) des groupements phosphates contenus dans les bioapatites des dinosaures. La méconnaissance de leur statut métabolique, ainsi que la disparition brutale de l essentiel du groupe à la fin du Crétacé nous a toutefois contraints à comparer leur enregistrement isotopique avec celui des chéloniens et crocodiliens associés, reptiles encore représentés actuellement. Une équation de fractionnement phosphate eau a été établie pour les crocodiles actuels et sa similitude avec celle déjà établie pour les tortues aquatiques indique un fractionnement isotopique comparable chez ces deux reptiles. Des mesures réalisées sur les restes dentaires de divers taxons de dinosaures crétacés ainsi que sur les restes de crocodiles et tortues associées montrent une différence significative entre ces deux groupes, différence observée actuellement entre les mammifères (endothermes) et les reptiles (ectothermes). Interprétées en termes d écarts de températures, ces différences suggèrent que les dinosaures étaient endothermes et conservaient une température constante de l ordre de 37C quelle que soient celles de leur environnement. A partir de ces mêmes mesures, un gradient latitudinal de températures moyennes de l air a été calculé pour l intervalle Campanien supérieur Maastrichtien moyen. Ce gradient est relativement faible (0,4/Lat.) mais suggère l existence de glaces aux pôles. Il est par ailleurs en bon accord avec les estimations déjà publiées. La validité de cette méthode ouvre de nouvelles perspectives pour l étude des climats antérieurs au Crétacé terminal, ainsi que pour l approche de la thermophysiologie des vertébrés terrestres plus anciens.LYON1-BU.Sciences (692662101) / SudocLYON1 - UFR Sciences de la terre (692662208) / SudocSudocFranceF