Browsing by Subject "Triassic"

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Diversity, ecology and response to climate change of Triassic temnospondyls: an integrative approach on global and regional scales
(2025) Moreno, Raphael; Schoch, Rainer
Temnospondyls are relatives of modern amphibians and represent a significant part of the fossil record of Triassic ecosystems. The Triassic was a period characterised by pronounced climatic and environmental changes. Due to their widespread occurrence temnospondyls offer unique insights into ecologically dynamic environments. In this dissertation, I apply an integrative approach on diverse geographic extents, including studies of global, regional and local measures and different stratigraphic scopes. Through a holistic framework of several methodologies, I aim to study the diversity and ecology of Triassic temnospondyls and their response to the changing Triassic climate. First, I present an extensive review of the global geographic and stratigraphic distribution of Triassic temnospondyls, before engaging in a detailed investigation of temnospondyl diversity within the German Triassic. Herein we identify 20 genera and 29 species of Triassic temnospondyls and advance the taxonomic identification through re-evaluations and identification of a new species occurring in the regional context of the German Triassic. Furthermore, we recognise three pronounced peaks of temnospondyl diversity coinciding with periods of enhanced ecological stability. In the second project, I employ species distribution modelling (SDM) to investigate the palaeogeographic distribution and potential dispersal routes of the temnospondyl fauna of the Central European basin and Central Pangea. I model the group response to changing environmental conditions during the Middle–Late Triassic transition, a period characterised by climatic fluctuations. Notably, this study is the first application of SDM on temnospondyls and highlights the dependency of temnospondyls on suitable abiotic conditions for their biogeographic distribution. Moreover, I quantify the changes in suitable habitat across various time slices from the Middle to Late Triassic period. Crucially, ecological resilience becomes evident as multiple clades persist through (1) phases of habitat reduction and (2) significant environmental and climatic changes. The utilisation of computational simulations on the deep time fossil record enhances our understanding of the interplay between dynamically changing climates and palaeobiological responses. The third project documents the ecological plasticity and adaptability of temnospondyls through new discoveries in depositional environments that have been previously deemed unsuitable for temnospondyl habitation. I assess and identify fragmentary remains of an unexpectedly diverse assemblage of temnospondyls in the sabkha and playa depositional environment of the Grabfeld Formation of southern Germany. The dolomitic banks that yielded some of the temnospondyl remains were deposited during brief marine ingressions from the Tethys Ocean into the Central European basin. The occurrence of sauropterygians and ostracods indicate euryhaline conditions. The identification of Metoposaurus in these layers challenges previous assumptions on the physiological tolerances of the group and further provides the stratigraphically oldest occurrence of this taxon in a global context. Furthermore, the occurrence of Plagiosternum in the same environment supports the general notion for the preferred palaeoenvironmental habitat of Plagiosternum while presenting the stratigraphically youngest occurrence of this taxon. In the last chapter, I investigate the palaeoenvironmental differences in the geographically close and coeval Middle Triassic fossil sites of Kupferzell and Vellberg-Eschenau in Baden-Württemberg, Germany. I investigate the geochemical properties in an attempt to characterise the degree of diagenetic alteration. Subsequent carbon and oxygen isotope analyses of tooth enamel of the temnospondyl Mastodonsaurus giganteus, as well as subsequent analyses of dental and skeletal bioapatite of associated fauna, reveal a substantial variation in the palaeoenvironments of both fossil localities. While both palaeoenvironments are characterised as lacustrine ecosystems, the observed isotopic differences portray Kupferzell as a more stable depositional environment with less episodic fluctuations, while the lacustrine system of Vellberg-Eschenau, especially layer E6, is depicted as more dynamic with greater seasonal and hydrological variabilities. Furthermore, the investigation of intra-tooth sample series fits the interpretation of a seasonally more dynamic setting in Vellberg-Eschenau E6. Overall, this dissertation demonstrates the effectiveness of eclectic approaches to elucidate complex ecological signals in Triassic temnospondyls. Additionally, the integrative framework applied in this dissertation accentuates and refines traditional views of temnospondyl palaeobiology and expands our perspective on the ecology, biogeography and plasticity of these taxa, underscoring their crucial role in Triassic ecosystems. The data presented in this thesis offers a multitude of future research endeavours. By combining the results of this dissertation with other comprehensive data sets the potential for continued advances in broader Triassic vertebrate palaeontology will be greatly enhanced, enabling significant insights into biodiversity patterns, evolutionary processes and ecological responses to environmental fluctuations.
Ontogenetic variation in the cranium of Mixosaurus cornalianus, with implications for the evolution of ichthyosaurian cranial development
(2023) Miedema, Feiko; Bindellini, Gabriele; Dal Sasso, Cristiano; Scheyer, Torsten M.; Maxwell, Erin E.
Relatively complete ontogenetic series are comparatively rare in the vertebrate fossil record. This can create biases in our understanding of morphology and evolution, since immaturity can represent a source of unrecognized intraspecific variation in both skeletal anatomy and ecology. In the extinct marine reptile clade Ichthyopterygia, ontogenetic series were widely studied only in some Jurassic genera, while the ontogeny of the oldest and most basal members of the clade is very poorly understood. Here, we investigate cranial ontogeny in Mixosaurus cornalianus , from the Middle Triassic Besano Formation of the Swiss and Italian Alps. This small-bodied taxon is represented by a wealth of material from multiple size classes, including fetal material. This allows us to assess ontogenetic changes in cranial morphology, and identify stages in the ontogenetic trajectory where divergence with more derived ichthyosaurs has occurred. Early ontogenetic stages of Mixosaurus show developmental patterns that are reminiscent of the presumed ancestral (early diverging sauropsid) condition. This is prominently visible in the late fetal stage in both the basioccipital, which shows morphology akin to basal tubera, and in the postorbital, which has a triradiate head. The ontogenetic trajectory of at least some of the cranial elements of Mixosaurus is therefore likely still very akin to the ancestral condition, even though the adult cranium diverges from the standard diapsid morphology.