Research projects

PD Dr. Torsten Scheyer
Sensory Palaeoecology in Secondary Aquatic Reptiles – The Radiation of Independent Triassic Marine Reptile Lineages following the Earth’s Largest Mass Extinction Event
April 2014 to March 2017
Funding sources
SNF (Personen- und Projektförderung)
Prof. Dr. Olivier Rieppel, Field Museum, Chicago (United States)
Prof. Dayong Jiang, Department of Geology and Geological Museum, Peking University, Beijing (China)
Prof. Chun Li, Institute of Vertebrate Paleontology and Paleoanthropology, Beijing (China)
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Interaction of organisms with their environment necessitates the use of sensory systems with which they perceive and respond to their surroundings. Palaeobiological investigations of evolutionary radiations would greatly benefit from a better understanding of sensory ecology features and their changes over geological time, especially in episodes of major habitat use innovation, as in the invasion of aquatic environments. As nervous and sensory organ systems adapt over time to the habitat, changes in the environment and habitat use entail, in cases, profound physiological and anatomical changes of the organism. Times of biotic crisis, i.e., global-scale mass extinction events usually followed by radiation phases with high evolutionary rates, have enormous significance both on the environmental and the organismal level. As such, following the catastrophic End-Permian mass extinction, the Early Triassic marked the start of several reptile lineages independently returning into marine environments. Herein I thus propose to study the palaeobiology and sensory palaeoecology of extinct vertebrates, by investigating the early evolution and secondary marine radiation of independent diapsid reptile lineages. The main lineage to be investigated are basal sauropterygians (including placodonts, nothosaurs, pachypleurosaurs and pistosauroids), whereas the fish-like ichthyosaurs (Ichthyopterygia) and thalattosaurs (Thalattosauria) are chosen as successive outgroups. These three lineages have the highest generic and specific diversity and broadest distribution of fossil marine reptiles from the Triassic. To date, the basal sauropterygians (with the exception of pistosaurs, the group most closely related to Plesiosauria) are known only from the Tethys Ocean, whereas thalattosaurs and ichthyosaurs were almost globally distributed. To various degrees, all three groups show modifications of their body plan in accordance with their aquatic lifestyle. This often leads to convergent evolution in their cranial and postcranial anatomy, hampering our understanding of the palaeobiology and evolutionary relationships of these animals. By increasing our knowledge of the changes involved in the secondary adaptation to an aquatic lifestyle in these groups, we achieve a better understanding of similar radiations in other times in Earth’s history as well, including today’s marine animals. The sensory organ systems of vertebrates include the five major senses (sight, hearing, smell, taste and touch), as well as some special senses such as echolocation and electroreception. Little is known however about the sensory array present in extinct marine reptiles, and in different groups some senses might be enhanced or reduced relative to others. But what are the osteological correlates of sensory organs preserved in the three lineages of extinct marine reptiles to be studied? How do these differ in comparison to modern aquatic animals? And how do ontogenetic changes provide information on changes in sensory ecology and phylogeny? The following hypotheses will be addressed: 1) Osteological correlates of sensory organ systems between fossil and extant reptiles are homologous. 2) New data gained from evidence-based reconstructions and interpretations of soft-tissue anatomy of fossils can refine phylogenetic interpretations of the extinct marine reptiles studied. 3) A better understanding of the radiation of secondary marine reptiles during the Triassic, the first of several of such radiations during the Mesozoic, sheds light on the complexity of ancient marine ecosystems. 4) Sensory organ systems and their osteological correlates are changing with increasing adaptation to the aquatic environment, i.e. from semi-aquatic forms to coastal dwellers to truly pelagic cruising forms.
Palaeoecology, micro-tomography, skull anatomy, marine reptiles, Ichthyopterygia, Sauropterygia, Thalattosauria, Triassic