Thèses sur le sujet « Marine reptile »

Jurassic marine ecosystems (ca. 201-145 million years ago) were dominated by three different lineages of reptiles - plesiosaurians, ichthyosaurs and thalattosuchian crocodylomorphs. Stratigraphic and fossil evidence indicates that these animals, like their modern counterparts, were able to coexist in the same environment for over ~50 million years from the Early Jurassic (~180 million years ago) to the Early Cretaceous (~130 million years ago). Marine reptile ecosystems were often very diverse, and included animals from different lineages, of disparate body-size and inferred ecology living alongside each other in the same environment. This unusual diversity suggests that marine reptiles formed complex ecosystems, and may have occupied analogous ecological roles today held by large fish, sharks, crocodiles, sirenians, and cetaceans. However, these comparisons are essentially qualitative, as they are based on the recurring convergent morphologies of skulls, mandibles and dentitions in aquatic tetrapods. Yet, they have never been quantitatively tested. Furthermore, although we have a comprehensive understanding of the anatomy, systematics, phylogenetic relationships, physiology and feeding ecology of these extinct animals, little is still known about the structure and evolution of their ecosystems. Thus, we do not understand what enabled marine reptiles to form complex assemblages, how their fauna changed through time, and more importantly how climatic and environmental changes shaped their long-term evolution. Answering these questions is essential because understanding past marine ecosystems may inform on whether and how modern ones can adjust to changes in the ocean temperature, chemistry and sea-level. In order to establish the reliability of these comparisons, in this project, I consider the evolution of the diverse marine reptile fossil assemblage of the Jurassic Sub-Boreal Seaway (JSBS) of the UK. The fossil record of the JSBS is an ideal case-study for many reasons. Firstly, it is a well-documented, high-diversity ecosystem, represented by hundreds of well-preserved specimens collected from the world-famous Oxford Clay Formations (OCF Callovian-early Oxfordian, late Middle to early Late Jurassic) and Kimmeridge Clay Formation (KCF - Kimmeridgian to Tithonian, Late Jurassic). These specimens have been intensively collected since the XIX century, and are available in museum collections. Secondly, the fossil record of the JSBS covers a continuous interval of ~18 million years (middle Callovian-early Tithonian ~166-148 million years ago) of marine reptile evolution, in a single seaway, during a time of well-documented environmental changes. These changes in sea-level, temperature and chemistry happened in concert with drastic changes in the composition between the OCF and KCF marine reptile faunas across the Middle-Late Jurassic boundary. Unfortunately, to date, the attempts to understand whether there is a correlation between these events have been hampered by the scarcity of fossils material from the intermediate layers of the Oxfordian 'Corallian Gap'. After a brief introduction (Chapter I), this project articulates in two parts. In the first descriptive section (Chapters II, III and IV), I set the bases for the second part by reviewing the fossil record of ichthyosaurs, plesiosaur and thalattosuchians of the JSBS. Particular emphasis was put on the systematics of thalattosuchian crocodylomorphs, and the fossil assemblage of the 'Corallian Gap'. The second part of this thesis is an analytical section (Chapters V and VI), in which, using a suite of numerical techniques, I investigate the ecology, evolution and feeding ecology of marine reptiles through time. A summary of the main conclusions and future directions are presented in Chapter VII. Chapter II is a description of a new genus and species, Ieldraan melkshamensis, a metriorhynchid thalattosuchian from the Callovian of England. The stratigraphic occurrence of this new taxon demonstrates that all the macrophagous lineages of Late Jurassic metriorhynchids originated in the Middle Jurassic, earlier than previously supposed. This also has important implications for the evolution of macropredatory features (particularly the dentition) in this group. In Chapters III and IV, I review the scarce fossil record of the Oxfordian 'Corallian Gap', the least studied stage of the considered ~18 million-year interval. The results show that despite the scarcity and poor preservation of materials compared to the underlying and overlying fossil-rich OCF and KCF, a large variety of marine reptiles lived in the JSBS during the 'Corallian Gap' (middle-late Oxfordian). The study confirms a drop in marine reptile diversity in the Oxfordian, exemplified by the demise of several OCF taxa, but partially counterbalanced by the contemporaneous radiation of some KCF lineages. This review confirms that a faunal turnover severely affected the composition of the JSBS across the Middle-Late Jurassic boundary, and I hypothesise that these faunal changes may have been driven by environmental perturbations during the Oxfordian. In Chapter V, I use the most common marine reptile fossils - teeth - and the revised stratigraphic occurrences of the JSBS (from the previous Chapters), to investigate the evolution of marine reptile groups, through time. Using a multivariate approach I established a quantitative system to assign species to dietary guilds based on dentition features that together with the availability of teeth, allowed examination of diversity and disparity patterns at unprecedented time, and systematic resolutions. The results show that different taxonomic/dietary groups did not overlap, suggesting partitioning of resources based on diet/feeding strategy. The analyses show a decline of shallow-water specialists, the diversification of macrophagous species, deep-diving taxa, and increasing body-size in concert with a deepening of sea-level across the Middle-Late Jurassic boundary. These trends are not accompanied by drops in disparity, but by a selective decline/increase of specific ecological guilds, that mimic the transition from shallow/nearshore to deeper/offshore habitats in modern cetacean coastal assemblages. In Chapter VI, I use a variety of multivariate techniques to present a quantitative assessment of the feeding behaviour of marine reptiles. The aim of this study is investigating the morphological and functional variation of ichthyosaur, plesiosaur and thalattosuchian lower jaws. This is done using a variety of multivariate techniques, and a biomechanical comparative approach. The analyses confirm previous qualitative observations that the ecosystems in the OCF and KCF were markedly distinct in faunal composition and structure. Phylogenetically closely related taxa preferentially cluster together, with minimal overlaps amongst groups in the morphospace. Focus examinations of key morphofunctional complexes reveals that marine reptile subclades are characterised by different combinations that are consistent with their inferred feeding ecologies (based on tooth morphology). Overall, the present quantitative results validate previous qualitative hypothetical feeding ecologies, and reveal multiple instances of morphofunctional convergent evolution. Overall my results also show that, like in modern ocean ecosystems, complex mechanisms of niche and habitat partitioning may have facilitated the coexistence of diverse marine reptile assemblages over tens of millions of years of evolutionary time.

This study has looked at an assemblage of fossilised teeth from Mesozoic marine amniotes from the Kristianstad basin in southern Sweden in order to make an estimate of the ecomorph diversity within said assemblage through looking at the morphology of the teeth. This was done as a pilot study to see if further studies would be able to produce worthwhile results. The assemblage consists largely of isolated tooth crowns, mostly from small- to medium sized mosasaurs such as Clidastes and Eonatator, but also contains larger mosasaurs, as well as a couple of plesiosaurs and one species of a marine crocodile. The analysis was performed on images of teeth using software developed for use in morphometrics. The resulting graphs imply a division into three guilds; the first represented by the short and blunt teeth of the crocodilian, the second by the elongated teeth of the plesiosaurs, and the third by the knife-like teeth of the mosasaurs. Since the mosasaurs overlap to a high degree in tooth shape, but also show quite diversity in size, it is possible the main dividing factor would have been size rather than type of prey. Further studies would be able to get a more accurate image of the ecology of this fauna by increasing the number of specimen in the analysis as well as taking into consideration more factors from other studies of similar taxa, such as jaw sizes, bite marks and gut contents.
Det här arbetet har studerat fossila tänder tillhörande Mesozoiska marina amnioter från Kristianstadsbassängen i södra Sverige, med avsikt att göra en uppskattning av den ekomorfa spridningen inom gruppen genom att studera tändernas form. Detta är enbart en pilotstudie för att se om fortsatta studier kan ge givande resultat. Det studerade materialet är en del av en samling till stor del bestående av enbart lösa tandkronor, mest från små till medelstora mosasaurier, såsom Clidastes och Eonatator, men även från större mosasaurier, så väl som ett par plesiosaurier och en marin krokodil-art. För analysen användes en programvara specifikt utvecklad för morfometri. De resulterande graferna antyder en indelning i tre “gillen”; det första representeras av de korta och trubbiga tänderna tillhörande krokodilen, det andra av de långsmala tänderna hos plesiosaurierna, och det tredje av de knivlika mosasaurietänderna. Eftersom mosasaurierna överlappar till stor grad gällande formen på tänderna, men skiljer sig mycket åt i storlek, så är det troligt att det snarare var storleken på bytesdjuren, och inte vilken typ, som skiljde dem åt. Framtida studier skulle kunna ge en bättre bild av den här faunans ekosystem dels genom att inkludera fler exemplar i analysen, och dels genom att inkludera andra faktorer från studier av liknande taxa, såsom käkstorlek, bitmärken och maginnehåll.

Le climat affecte entre autre la phénologie, l’aire de distribution, le comportement et la physiologie des espèces. Le changement climatique a donc des répercussions sur chacun de ces facteurs. L’augmentation globale des températures prévue d’ici 2100 pourrait profondément modifier la biodiversité de l’échelle des espèces jusqu’à celle des écosystèmes. Les ectothermes, et en particulier les reptiles ovipares à détermination du sexe sensible à la température, font partie des organismes susceptibles d’être les plus vulnérables au réchauffement du climat puisque quasiment tous leurs traits d’histoire de vie dépendent de la température. L’origine et le maintien de ce mécanisme de détermination du sexe, pouvant conduire à un sex ratio fortement biaisé à l’échelle d’une population, reste une énigme pour les écologues. Parmi les nombreuses questions soulevées par la présence de ce mécanisme de détermination du sexe, la signification adaptative, s’il y en a une, de ce mécanisme est cruciale.Ce mécanisme de détermination du sexe rend-il les espèces plus vulnérables dans le contexte actuel du changement du climat ? Plusieurs hypothèses évolutives ont été proposées et des modèles de dynamique des populations sont disponibles pour répondre à ces questions. Cependant, prédire le sex ratio primaire en conditions naturelles, c’est-à-dire le sex ratio des nouveaux nés, reste un défi majeur à l’heure actuel. Ce manuscrit vise à apporter de nouveaux outils méthodologiques afin de correctement prédire le sex ratio d’une ponte en fonction de la température ressentie par les embryons au cours de l’incubation. Les tortues marines,quasiment toutes menacées, sont des espèces migratrices présentant toute ce mécanisme de détermination du sexe.Chez ces espèces, la phénologie des pontes est aussi sensible à la température du milieu. Ce type de plasticité phénotypique est probablement la stratégie la plus efficace pour pallier à un changement rapide du climat. Ce manuscrit apporte quelques éléments de réponse quant au potentiel adaptatif des tortues marines face au réchauffement climatique avec l’exemple de plusieurs populations de tortues Caouanne (Caretta caretta)
Climate affects, among other things, species’phenology, distribution range, behavior and physiology.Climate change thus impacts each of these factors. Global warming expected by 2100 might profoundly modify biodiversity from species to ecosystems. Ectotherms, and in particular oviparous reptiles with temperature dependent sex determination, are thought to be among the most vulnerable in the face of global warming because virtually all their life history traits depend on temperature.The origin and the persistence of temperature-dependent sex determination, which could lead to heavily biased population sex ratios, is still an enigma for ecologists. Among numerous issues related to this sex determining mechanism, understanding its adaptive significance, if there is one, is crucial. At another level, does this sex determining mechanism make species more vulnerable in the context of contemporary climate change ? Several evolutionary hypotheses have been proposed and population dynamic models are available to address these issues. However, predicting primary sex ratio, i.e., the sex ratio of hatchlings, in natural conditions currently remainsa challenge. This manuscript aims to bring new methodological tools to properly predict sex ratio of aclutch depending on temperature experienced by embryosthroughout incubation. Marine turtles, almost all being threatened, are migratory species that all exhibit this sex determining mechanism. For those species, nesting phenology is also sensitive to environmental temperature.This type of phenotypic plasticity is probably the most efficient strategy to keep up with rapid climate change.This manuscript provides some elements for understanding the adaptive potential of sea turtles in the face of global warming with the example of several)

The Besano Formation consists of an alternation of laminated dolomitic banks and bituminous shales, and sparse cineritic tuffs that are dated as Late Anisian–Early Ladinian. It is one of the richest fossil-bearing formations from the Monte San Giorgio area; on the Italian side of Monte San Giorgio, the Sasso Caldo site is the one from which the greatest part of the Besano collection housed at the Museo di Storia Naturale di Milano is from. This Ph.D. thesis aims to the study of the Besano Formation macrofauna, through biochronostratigraphic zonation of the Sasso Caldo Site, revision of the large ichthyosaur Besanosaurus leptorhynchus), and study of the most important specimens, chosen for their preservation and rarity, but also to test the hypothesis of variations in the influence of open sea on the Besano basin. All the available ammonoids and bivalves from the Sasso Caldo site (Besano Formation), housed in the collections of the Museo di Storia Naturale di Milano, were examined and determined. The systematic study led to the recognition of 15 ammonoid taxa belonging to 10 genera, and five species belonging to the bivalve genus Daonella. The study of bed-by-bed collected specimens allowed the biochronostratigraphic classification of the Sasso Caldo section and the time-calibration of invertebrate and vertebrate bioevents. Results evidence that at Sasso Caldo site crops out almost the entire middle to upper Besano Formation. corresponding the Nevadites secedensis ammonoid zone. The trend of distribution of specimens reflects the establishment of an intraplatform basin with discontinuous open-marine influence in the middle Besano Formation, while the upper Besano Formation corresponds to a shallower subtidal restricted platform environment. Among the terrestrial taxa recovered at Sasso Caldo from the upper Besano Formation, a remarkably well-preserved fossil scorpion (BES SC 1973) is described in this thesis. This finding corroborates the hypothesized existence of a near shoreline during the deposition of the upper Besano Formation. BES SC 1973 is assigned to a new taxon gen. et sp. nov., included in the family Protobuthidae. This finding represents the first arachnid recorded from the Besano Formation, and the second genus attributed to the family Protobuthidae. This specimen is also the first reported Italian Mesozoic fossil scorpion. Regarding vertebrates, MSNM V927 and 928, a portion of the axial skeleton of a large diapsid, is attributed to Helveticosaurus zollingeri, a rare diapsid known only from the Besano Formation. This animal was recovered in association with the ammonoid Ticinites, at the base of the N. secedensis Zone, in coincidence with the establishment of the intraplatform basin of the middle Besano Formation. This specimen is the first record of skeletal remains and the second specimen assigned to the taxon in Italy. In this work the niche occupied by this animal in the Middle Triassic coastal ecosystems and its swimming style are also revised and discussed. MSNM V926, and SMNS 50010, respectively a portion of ribcage and an isolated partial forefin of a large ichthyosaur, were attributed to Cymbospondylus buchseri. MSNM V926 represents the first specimen attributed to this taxon and recovered on the Italian side of Monte San Giorgio. A great part of this thesis is dedicated to the revision of Besanosaurus leptorhynchus. The specimens studied and attributed to Besanosaurus leptorhynchus preserve a remarkably complete cranial and postcranial anatomy so that this taxon can be now accounted among the best-understood Middle Triassic ichthyosaur taxa. The revision of the skull morphology of this taxon clarified long-standing controversies regarding its cranial anatomy and the taxonomy of shastasaurids from Monte San Giorgio. The six specimens here described represent a potential ontogenetic series composed of an embryo (inside the maternal cavity of BES SC 999), likely two subadults, and four adults. They can be ordered by increasing size as follows: embryonic material of BES SC 999, PIMUZ T 4376, PIMUZ T 1895, BES SC 999, BES SC 1016, GPIT 1793/1, PIMUZ T 4847. Also, Besanosaurus resulted the largest Middle Triassic ichthyosaur taxon of the Western Tethys to date, since a full adult size is confidently estimated to be almost 8 m in PIMUZ T 4847. Besanosaurus is characterized by a long, slender, and gracile snout, representing an ecological specialization never seen before the Anisian in a large-sized diapsid. The study of the postcranial anatomy of Besanosaurus leptorhynchus is based on four specimens: PIMUZ T 4376, PIMUZ T 1895, BES SC 999, PIMUZ T 4847. The results suggest that this taxon possesses a peculiar bauplan, which in its proportions fits in between Cymbospondylus and the shastasaur-grade ichthyosaurs. Swimming capabilities of Besanosaurus leptorhynchus were tested and compared with Cymbospondylus and Mixosaurus. Among the ichthyosaurs from the Besano-Monte San Giorgio fauna (Cymbopondylus, mixosaurids, and Besanosaurus), different hunting strategies, demonstrated by different morphologies and dimensions of the rostra, as well as different body proportions and swimming styles, should have led to niche partitioning. The key phylogenetic position occupied by Besanosausurus leptorhynchus in the ichthyosaurian phylogeny was investigated: the analysis shows that this taxon represents the basalmost member of shastasaur-grade ichthyosaurs, recovered to be a paraphyletic group. Eventually is addressed a study of the embryonic material preserved in BES SC 999. We deem the material in the body cavity of BES SC 999 unambiguously embryonic and attributable to Besanosaurus leptorhynchus. Here the embryonic material is described in detail and qualitatively compared with the maternal specimen and to other known ichthyosaur prenatal specimens.

Marine upwelling occurs when surface currents diverge or are deflected. Deeper water, often nutrient-rich, rises and generates a cascade of biological effects including elevated productivity and a unique assemblage of organisms. Macrofaunal characteristics of upwelling provide key evidence for oxygen-minimum zones, upwelling of cool water, and high productivity and are potentially useful indicators of ancient upwelling. The Upper Triassic Luning Formation in Nevada contains abundant, large ichthyosaurs and was deposited in a back-arc basin that could have experienced upwelling conditions. Luning Formation rocks at West Union Canyon were analyzed for sedimentological, geochemical, and paleontological upwelling indicators. Abundant suspension feeders, lack of corals and calcareous algae, modest total organic carbon and minor element concentrations in deeper marine facies, abundant cosmopolitan molluscs but no taxa restricted to low latitudes, and abundant fecal pellets and clotted fabrics in most facies suggest that upwelling could have influenced Luning deposition. Moderate-scale upwelling likely contributed to eutrophic conditions and ichthyosaur abundance at West Union Canyon. Marine reptiles might have had ties to upwelling areas to provide food, as do modern whales. A relational database containing 817 locality records and 1365 taxon-localities was assembled for ichthyosaurs, plesiosaurs, and mosasaurs. Marine reptile localities were compared with model-predicted upwelling and with upwelling-related lithologies (organic-rich rock, biogenic silica, phosphorite, and glauconite). Marine reptile occurrences intersected predicted upwelling more often than expected by chance for the Upper Cretaceous, Callovian, and Norian stages, and for all of the data together (P = 0.05). For age-restricted data, occurrences of Mosasauridae, Pliosauridae, and Plesiosauria intersected upwelling more often than expected by chance (P = 0.05). Average shortest distances between reptile fossil and upwelling lithology occurrences were smallest (one grid cell adjacent or smaller) for the Pliensbachian and four of five Cretaceous stages. Analytical biases and other aspects of reptile ecology may have affected the results, but overall, upwelling could have influenced marine reptile distribution, particularly for the Upper Cretaceous. Multiple radiations into the high-productivity, top-predator niche over the Mesozoic are suggested by the dominance of different taxa in grid cells containing upwelling lithologies: ichthyosaurs (early Mesozoic), plesiosaurs (middle Mesozoic), and finally mosasaurs (late Mesozoic).

The primary goal of numerical palaeobiology is to understand the processes that generate and eliminate extinct and extant biodiversity. It is important to examine key clades and adaptive assemblages, whose evolution appears intrinsically related to major events in deep time. Mesozoic marine reptiles represent an excellent candidate for investigation, having ascended to ecological dominance in the aftermath of the Permo-Triassic mass extinction and passed through multiple biotic crises. Observations from the rich Triassic marine reptile fossil record highlight diverse ecologies, providing tentative evidence for an exceptional radiation driven by new trophic opportunities - but quantitative tests for this are scarce. Others have highlighted the potential long-term impacts of extinction, and revealed that ichthyosaur evolution was reset following an extinction interval in the Late Triassic. Although a recent body of research has provided new insights into marine reptile macroevolution, many questions remain unanswered. In this thesis, I present several diverse case studies exploring the impacts of ecological opportunity and biotic perturbations in Mesozoic marine reptile macroevolution. Throughout, focus is placed on examining temporal and group-wide patterns of morphological and functional diversity (disparity) and testing rates of phenotypic evolution. Chapters 2-4 focus on Sauropterygia, the most diverse and ecologically disparate Mesozoic marine reptiles, while chapter 5 incorporates all Mesozoic marine reptiles as an inclusive adaptive assemblage. In brief, results show that the Triassic was a time of unusual diversification and high disparity in marine reptile evolution. Multiple lines of evidence show the Triassic was a time of marked morphological, functional and ecological proliferation. Results herein also reveal that sauropterygians, and marine reptiles as a whole, passed through a macroevolutionary bottleneck during the Late Triassic, similar to that identified for ichthyosaurs previously. Overall, this thesis supports the idea that major extinction events can have disproportionate effects on macroevolution, by catalysing exceptional radiations in their aftermath.

Un inventaire des reptiles marins connus du trias inferieur jusqu'au paleocene est presente: 46 familles, environ 200 genres et 400 especes ont ete recenses. Cette base de donnees inclut des commentaires sur la systematique, les extensions stratigraphiques et la distribution geographique des taxons. Les reptiles marins regroupent une mosaique de formes comprenant des groupes exclusivement marins (ichthyosaures, nothosaures, placodontes, thalattosaures, hupehsuchiens, plesiosaures, pliosaures) aussi bien que des groupes encore connus actuellement et qui incluent des representants continentaux (crocodiles, lezards, serpents, tortues). Le registre fossile des reptiles marins a ete ponctue par deux extinctions en masse: la transition ladinien-carnien (64% des familles) affecte preferentiellement les formes infeodees au milieu cotier. Cette extinction coincide avec une phase de regression importante. Durant le trias superieur, une reorganisation faunique aboutit a la disparition progressive des formes littorales et a la mise en place de groupes pelagiques. Durant la crise maastrichtien-danien (36% des familles), les formes pelagiques de grande taille, a savoir les mosasaures et les plesiosaures, sont les plus touchees et leur extinction s'inscrirait plutot dans un modele catastrophique que gradualiste. Au contraire, les pliosaures et les tortues protostegides s'eteignent alors qu'ils etaient deja sur le declin. Les survivants sont des groupes littoraux de taille moderee comme les crocodiles, serpents et certaines tortues qui auraient pu trouver refuge en milieu dulcaquicole. Une rupture de la chaine alimentaire tributaire du phytoplancton est proposee comme scenario d'extinction pour les formes pelagiques

Les trois groupes de reptiles marins du trias, ichthyopterygiens, sauropterygiens et placodontes, sont analyses globalement. Leur revision aboutit a reconnaitre 114 especes valides pour lesquelles une analyse phylogenetique est proposee. Les caracteristiques ecologiques (locomotion, regimes alimentaires) des trois groupes sont etudiees afin de determiner leurs potentialites de dispersion. La confrontation de leur distribution geographique et de ces potentialites de dispersion, aux reconstitutions paleogeographiques du trias conduisent a proposer plusieurs modeles de dispersion

L’étude de la composition isotopique de l’oxygène de l’émail des dents de vertébrésconstitue une méthode fiable de reconstitution des paléotempératures, grâce àl’interdépendance entre le δ18O de l’apatite des dents, le δ18O des fluides corporels, del’eau ingérée et la température du milieu. L’amélioration et la miniaturisation des techniquesanalytiques a permis d’augmenter la résolution du signal reconstitué, depuis les variations detempérature sur de grandes échelles de temps jusqu’aux variations saisonnières durant laformation de la dent. Cependant, ces variations du δ18O de la dent ne sont pas uniquementdépendantes des variations de température du milieu, mais peuvent également êtreaffectées par d’autres paramètres climatiques, comme la répartition des précipitations aucours de l’année, ou biologique, comme le mode de minéralisation de la dent, l’alimentation,la physiologie de l’animal ou des migrations.Les paramètres biologiques peuvent être estimés dans le cas de taxons possédantdes parents proches dans la faune actuelle. Par exemple, la connaissance des processus deformation et de minéralisation des dents de bovinés actuels permet d’interpréter le signalisotopique de l’oxygène enregistré dans les dents de bovinés fossiles. Ainsi, l’analyse dedents de Bison priscus provenant de l’aven de Coudoulous (Lot, France) a permis dereconstituer les variations saisonnières de température au cours de l’avant-dernier épisodeglaciaire (MIS 6) au Pléistocène moyen, lorsque la région servait de terrain de chasse àHomo neanderthalensis. Le climat était à cette époque plus froid de 4°C en moyenne, maisavec des saisons nettement plus contrastées. Ainsi, si les températures estivales étaientidentiques aux valeurs actuelles, les températures hivernales étaient plus basses de 6-7°C.En milieu marin, les variations saisonnières de température affectent uniquement leseaux de surface. Les plaques dentaires de myliobatidés, un groupe de raies pélagiquesvivant principalement entre 0 et 100 mètres de profondeur, sont un outil potentiel pourreconstituer la paléosaisonnalité. L’étude de plaques dentaires de Myliobatis et deRhinoptera actuels montre que la composition isotopique des dents de ces animauxenregistre des variations de température et de δ18O des eaux de surface. Ainsi, il est doncpossible de reconstituer les caractéristiques des masses d’eau traversées par l’animal. Cetoutil a également un intérêt paléoécologique car il permet de mettre en évidence d’éventuelscomportements migratoires, comme chez certains myliobatidés actuels. L’étude despécimens d’Aetomylaeus provenant du Pliocène de Montpellier (Hérault, France) montredes températures 5°C plus élevées par rapport aux v aleurs actuelles
The oxygen isotopic composition of the vertebrate tooth enamel is a reliable proxy toreconstruct paleotemperatures based on the dependence of the δ18O of the tooth apatite onthe δ18O of body fluids, on the δ18O of the drinking water, and on the environmentaltemperature. The improvement and the miniaturization of the analytical procedures allowedincreasing the resolution of the reconstructed signal, from paleotemperature variations overgeological times to seasonal variations during the tooth growth. However seasonal variationsof the enamel δ18O do not only depend on temperature variations but can also be influencedby other climatic parameters such as rainfall distribution over the year, or by biological andecological parameters such as tooth mineralization process, diet, physiology or migratorypatterns.Biological parameters can be estimated based on the study of extant relatives inmodern faunas. For example, data on tooth formation and mineralization processes inmodern bovids allow a better understanding of the oxygen isotopic signal recorded in fossilbovid teeth. Thus reconstruction of seasonal variations of temperature during the penultimateglacial episode (MIS 6) has been made possible from the analysis of Bison priscus teethfrom the aven of Coudoulous (Lot, France). Climate was 4°C colder during the middlePleistocene when Europe was still Homo neanderthalensis hunting ground, and seasonswere more contrasted than today. Summer temperatures were similar to modern values, butwinter temperatures were 6-7°C colder.In marine environments, seasonal variations of temperature only affect surfacewaters. Myliobatids are pelagic rays living mostly between 0 and 100 m depth, thus theoxygen isotopic composition of myliobatid dental plates is a potential proxy to reconstruct thepaleoseasonality. The isotopic analysis of modern Myliobatis and Rhinoptera samplesconfirmed that variations of the sea-surface temperature (SST) and the δ18O of seawater arerecorded in the δ18O of myliobatid teeth. Thus it is possible to reconstruct the variations ofseawater temperature during a part of the animal’s life, but it also allows pointing outmigratory patterns in some myliobatid species. Reconstructions of seasonal variations ofSST during the middle Pliocene in Montpellier (Hérault, France) from the δ18O of myliobatiddental plates yielded paleotemperatures 5°C higher than modern values

Mixosaurid ichthyosaurs (mixosaurs) are a dominant group of Middle Triassic marine reptiles that was widely distributed in both Tethyan and Panthalassic terranes. They are represented by many excellently preserved specimens from all around the world and have been studied for more than one hundred years. Even so, their morphology is not adequately known. The systematics of mixosaurs is not well understood and their phylogeny has been controversial. The nomination of several Chinese mixosaurs makes the situation even worse. This thesis aims to provide a comprehensive review of Chinese mixosaurs and discuss their phylogenetic relationships. The detailed anatomy of only valid Chinese mixosaurid species Mixosaurus panxianensis is well established in this thesis. Its ontogenetic changes are also noted and a better diagnosis is given. A new morphotype of mixosaurs from a recently discovered fossil Lagerst?tte, the Luoping biota, is described in detail. This morphotype is similar to M. panxianensis but consistent differences are also present. The ecological comparison to M. panxianensis demonstrates that this morphotype represents a new taxon that is different from M. panxianensis. A nearly complete and articulated specimen of Phalarodon atavus from the Middle Triassic Luoping biota, Yunnan, South China is described. This is the first specimen of P. atavus discovered outside the Germanic Basin. The discovery of this specimen demonstrates a cosmopolitan distribution of P. atavus across the whole Tethyan ocean. The new specimen is also the first one preserving the postcranial anatomy of this species, providing the potential to evaluate its swimming ability for the first time. Functional morphology shows that this species is well adapted for a pursuit attack of prey, consistent with the distribution pattern of the species. Tooth crown morphology suggests that P. atavus may prefer externally soft prey such as belemnoids. Mixosaurs are divided into three ontogenetic stages based on the humeral morphology. The juvenile stage is characterized by a textured dorsal humeral shaft surface. The subadult stage is characterized by a smooth humeral shaft in dorsal view with a rugose humeral head. The adult stage is characterized by a smooth humeral head. The consistent presence of the surface texture of ventral humeral shaft is most probably caused by the strong muscle insertion presumably related to the function of steering of the fore fins in mixosaurs. Five morphotypes of Chinese mixosaurs are recognized in this study. Twenty-five more or less new characters are introduced to evaluate the phylogenetic relationships of mixosaurian-like specimens from China. The monophyly of mixosaurs including all studied Chinese morphotypes is well corroborated. Further investigation on the mixosaurs from Monte San Giorgio is recommended to resolve the phylogenetic relationships of mixosaurs.
published_or_final_version
Earth Sciences
Doctoral
Doctor of Philosophy

En reflétant une image plus ou moins fidèle du cerveau, l’endocrâne permet d’accéder au système nerveux des espèces fossiles. A partir de spécimens exceptionnellement préservés de mosasaures (Squamata) et de plésiosaures (Sauropterygia), provenant des affleurements turoniens de Goulmima (sud du Maroc), ce travail a pour but de décrire, pour la première fois en détail l'anatomie endocrânienne de ces deux grands clades de reptiles marins du Mésozoïque. Cette étude a pour but d’inférer leurs capacités sensorielles permettant de comprendre leur cohabitation, leurs interactions et leur position au sein du réseau trophique. L'anatomie endocrânienne des squamates actuels, principalement des serpents mais aussi des varans et des amphisbènes, presque inconnus jusqu'à présent, a également été étudiée à des fins comparatives afin d’analyser les relations forme-fonction associées aux endocrânes. La variabilité morphologique de l’endocrâne chez les squamates actuel démontre un signal phylogénétique mais également écologique. De plus, la taille relative de chaque structure endocrânienne révèle des différences de vision et d'olfaction selon les espèces. Parmi les taxons fossiles, la microtomographie a été utilisée pour reconstituer en détail la morphologie crânienne de trois nouveaux spécimens de plésiosaures. Deux de ces spécimens ont été assignés à l’élasmosaure Libonectes morgani et le troisième à un polycotylidé indéterminé. La morphologie 3D de l'endocrâne a été reconstruite pour ces spécimens ainsi que pour le mosasaure basal Tethysaurus nopcsai. La morphologie endocrânienne des plésiosaures diffère de celles retrouvées chez les vertébrés éteints et actuels. En se basant sur la taille relative des structures composant leurs endocrânes, le mosasaure Tethysaurus et les plésiosaures semblent davantage utiliser la vision que l'olfaction pour interagir avec leur environnement. Ces nouvelles données endocrâniennes, ajoutées aux informations déjà disponibles dans la littérature, suggèrent différents modes de locomotion et techniques de chasse, ce qui leur a probablement permis de coexister à Goulmima en tant que prédateur
As windows into the deep history of neuroanatomy, endocasts may provide information about the central nervous system of fossil taxa. Based on exceptionally preserved specimens of coeval mosasauroids (Squamata) and plesiosaurians (Sauropterygia), from the Turonian outcrops of Goulmima (Southern Morocco), the aim of this work was to describe for the first time in detail the endocranial anatomy of these two major clades of Mesozoic marine reptiles to provide insights about their sensory abilities, and thus to understand their cohabitation, interactions and niche partitioning. The endocranial anatomy of related extant squamates, mainly snakes but also varanids and amphisbaenians, also almost unknown until now, has been performed for the first time and used for comparative purpose to analyze the form-function relationships associated to endocasts. The analysis of the endocranial variability in extant squamates pointed out that endocasts reflect both phylogenetic and ecological signals, and that the relative size of each endocranial structure can be used to reveal differences in vision and olfaction according to taxa. Among fossil taxa, computed tomography was used to reconstruct in detail the cranial morphology of three unpublished specimens of Plesiosauria. These specimens have been examined and described, two have been referred to the elasmosaurid Libonectes morgani and the third one is an indeterminate polycotylid. The 3D morphology of the endocast has been reconstructed for these plesiosaurian specimens and the basal mosasauroid Tethysaurus nopcsai. The results show that the endocranial morphology of Plesiosauria differs from that know in other extinct and extant vertebrates. Based on the relative size of the structures composing their endocasts, both the mosasauroid Tethysaurus and the plesiosaurians seem to rely more on vision than on olfaction to interact with their environment. However, these new endocast data, added to information already available in the literature suggest different modes of locomotion and hunting techniques, which probably allowed them to coexist in Goulmima as quaternary consumers

L'etude systematique, taphonomique, paleoecologique et paleobiogeographique des fossiles de vertebres marins turoniens de la vallee superieure du magdalena, colombie, est presentee. Cette etude correspond au premier travail realise sur l'ensemble des vertebres turoniens de colombie. Le materiel considere comprend 26 specimens d'apres lesquels on reconnait 6 taxons de chondrichthyes, 4 taxons d'osteichthyes, et 4 taxons de reptiles. De ces taxons, 9 etaient inconnus en colombie. Un nouveau genre et deux nouvelles especes de teleosteens sont reconnus. Bien que le registre lithologique indique que les conditions de depot du bassin turonien de colombie etaient essentiellement anoxiques, l'etude paleoecologique des vertebres permet de proposer que la tranche d'eau presentait de bonnes conditions d'oxygenation. Ces conditions ont permis le developpement d'une chaine trophique du necton bien structuree, certainement soutenue par de grandes masses de plancton. Une large connexion du bassin avec l'ocean permettait probablement l'entree de courants riches en nutriments, ainsi que de vertebres pelagiques. Les fossiles etudies presentent une excellente conservation en trois dimensions. L'analyse taphonomique permet de proposer que des evenements anoxiques ont pu provoquer des mortalites subites du necton et que les restes ont ete deposes et enfouis a proximite du lieu de mort des organismes. Ils ont subi une lente decomposition sur le fond du bassin, sous conditions anoxiques. Les vertebres etudies representent apparemment un ensemble faunique developpe isolement dans la region nord-ouest de l'amerique du sud. Au niveau supra-specifique on peut pourtant observer des affinites, d'une part avec les faunes de l'ouest de l'afrique et, d'autre part, avec les faunes du nord de l'afrique et du sud de l'europe centrale. Ces faunes apparemment nouvelles en colombie, et en partie aussi dans le monde, semblent etre des faunes de recouvrement liees a la crise cenomano-turonienne.

The sand lizard (Lacerta agilis) reaches the northern periphery of its distribution in south-central Sweden, where small, isolated relict populations occur in pine heath forests on sandy sediments. Modern forestry and fire suppression have reduced the amount of suitable open habitat for the species in this area and seem to be important for its decline. Main objectives of this thesis were to evaluate the efficiency of different management strategies, and if the sand lizard can function as an umbrella species for biodiversity conservation. Over a 16-year period, the estimated annual numbers of adult females in each of two study populations fluctuated between 23 and 3. Simulations of stochastic future population growth showed that the risk of extinction was highly dependent on population growth rate, which in turn was strongly affected by juvenile survival as indicated by elasticity analysis. Simulations of population growth for 50 years showed that the quasi-extinction risk (threshold ≤ 10 females) was > 56% for patches ≤ 1 ha; which is the observed average size of suitable habitat for inhabited patches during a 10-year period. In managed metapopulation networks with highly co-fluctuating local populations, among-population dispersal was not important to reduce extinction risks over a 50-year horizon. In the field the preferred microhabitat of sand lizards was successfully restored using tree felling and patch-soil scarification. The lizards gradually colonized the restored patches, and 16 years after restoration, sand lizards where mainly found there. Pine-heath area, and patch area within individual pine heaths, were of major importance for long-term population persistence at regional and landscape scales, respectively. Analyses of nested species subsets and an umbrella index suggest that the sand lizard can be a useful cross-taxonomic umbrella species on both scales for other red-listed species.

L'étude de la composition isotopique de l'oxygène de l'émail des dents de vertébrésconstitue une méthode fiable de reconstitution des paléotempératures, grâce àl'interdépendance entre le δ18O de l'apatite des dents, le δ18O des fluides corporels, del'eau ingérée et la température du milieu. L'amélioration et la miniaturisation des techniquesanalytiques a permis d'augmenter la résolution du signal reconstitué, depuis les variations detempérature sur de grandes échelles de temps jusqu'aux variations saisonnières durant laformation de la dent. Cependant, ces variations du δ18O de la dent ne sont pas uniquementdépendantes des variations de température du milieu, mais peuvent également êtreaffectées par d'autres paramètres climatiques, comme la répartition des précipitations aucours de l'année, ou biologique, comme le mode de minéralisation de la dent, l'alimentation,la physiologie de l'animal ou des migrations.Les paramètres biologiques peuvent être estimés dans le cas de taxons possédantdes parents proches dans la faune actuelle. Par exemple, la connaissance des processus deformation et de minéralisation des dents de bovinés actuels permet d'interpréter le signalisotopique de l'oxygène enregistré dans les dents de bovinés fossiles. Ainsi, l'analyse dedents de Bison priscus provenant de l'aven de Coudoulous (Lot, France) a permis dereconstituer les variations saisonnières de température au cours de l'avant-dernier épisodeglaciaire (MIS 6) au Pléistocène moyen, lorsque la région servait de terrain de chasse àHomo neanderthalensis. Le climat était à cette époque plus froid de 4°C en moyenne, maisavec des saisons nettement plus contrastées. Ainsi, si les températures estivales étaientidentiques aux valeurs actuelles, les températures hivernales étaient plus basses de 6-7°C.En milieu marin, les variations saisonnières de température affectent uniquement leseaux de surface. Les plaques dentaires de myliobatidés, un groupe de raies pélagiquesvivant principalement entre 0 et 100 mètres de profondeur, sont un outil potentiel pourreconstituer la paléosaisonnalité. L'étude de plaques dentaires de Myliobatis et deRhinoptera actuels montre que la composition isotopique des dents de ces animauxenregistre des variations de température et de δ18O des eaux de surface. Ainsi, il est doncpossible de reconstituer les caractéristiques des masses d'eau traversées par l'animal. Cetoutil a également un intérêt paléoécologique car il permet de mettre en évidence d'éventuelscomportements migratoires, comme chez certains myliobatidés actuels. L'étude despécimens d'Aetomylaeus provenant du Pliocène de Montpellier (Hérault, France) montredes températures 5°C plus élevées par rapport aux v aleurs actuelles.

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The age of precious opal and the mechanisms that result in formation as opposed to the ubiquitous common opal are poorly understood. Until now, there has been no research on the replacement of biominerals in vertebrate bones by opal. As the microtexture, mineralogy and chemistry of bones are well-known, they provide a unique opportunity to study the mechanism of precious opal deposition. In this article chemical and textural features of Andamooka opalised plesiosaur bones were compared with those in non-opalised ichthyosaur bones from Moon Plain and a recent dolphin bone. Opalised wood samples from Nevada and White Cliffs were also studied to compare with bone opalisation and different depositional environments (sedimentary vs volcanogenic). The cellular form of a continuous irregular framework of silica was retained in the wood samples. The mineralogy of the wood samples reflects their depositional environment, where opal-CT and opal-C is dominant in volcanic deposits (Nevada) and opal-A in sedimentary deposits (White Cliffs). Comparison of the Nevada wood to Post-Archean average shale (PAAS) shows that it is rich in most trace elements with the exception of Y and U. The high amount of trace elements is a reflection of its volcanic origin. In contrast, the opalised wood from White Cliffs is depleted in most trace elements with the exception of Co. Cracks were observed in both the opalised wood and bone samples which allowed the void space required to form precious opal. The opalised wood from White Cliffs and the opalised plesiosaur bones from Andamooka are chemically very similar and reflect similar compositions for the opalising fluids. The Haversian system was preserved in the non-opalised ichthyosaur bone but not in the opalised bones. The ichthyosaur bone is comprised mostly of carbonate-hydroxylapatite but in the opalised bones the major mineral is quartz. Modern dolphin bone consists of bioapatite with water and organic material: its trace element composition is broadly similar to the ichthyosaur bone from Moon Plain but is richer in Sr, Zn and Co. When normalized to PAAS, the ichthyosaur bone is depleted in all trace elements with the exception of Sr, which is likely a product of the carbonate-rich mineralogy. Like the ichthyosaur bones, the opalised bones are also depleted in trace elements, with the exception of Co and Zn. There is no evidence of remnant bioapatite in the opalised bone, a finding consistent with the chemical analyses that show only trace amounts of Ca and no P. The level of microstructural preservation in the opalised bone suggests that opalisation is not a closely coupled dissolution-reprecipitation reaction and that there was a fluid filled space between the reaction fronts which allowed the opal silica spheres to form and settle within a comparatively small space (100 µm). An alternative interpretation is that the fibrous quartz filled the osteon canals before opalisation and that the bioapatite was then dissolved away leaving a hollow cast that filled slowly with opal.
Thesis (B.Sc.(Hons)) -- University of Adelaide, School of Physical Sciences, 2004