An isotopic investigation into the palaeoecology and niche partitioning of Thalattosuchia (Crocodylomorpha) in the Posidonia Shale, Germany

• Applicant: Dr. Michela Johnson
• Subject Area: Palaeontology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 542399601

Thalattosuchia is a clade of successful crocodylomorphs thatdominated the coastlines during the Early Jurassic, comprised of two groups, Teleosauroidea and Metriorhynchoidea. Thalattosuchians represent a key, diverse component of Early Jurassic ecosystems, and began experimenting with multiple ecomorphologically significant features early on in their evolution. Four teleosauroids and one metriorhynchoid appear to have lived sympatrically in the Early Jurassic Posidonia Shale Sea. These species display distinct morphological features, such as a heavily ornamented dorsal armour shield in Platysuchus, laterally-facing eyes in Pelagosaurus and Plagiophthalmosuchus, and more robust dentition in Mystriosaurus that clearly suggest some type of dietary or habitat partitioning. However, while recent studies have evaluated the anatomy and ontogeny of this group, the intricacies of how they partitioned food sources and habitats is poorly understood, which is surprising given the amount of fossils that are available. For this project, I aim to provide a comprehensive, in-depth evaluation of Early Jurassic thalattosuchian palaeoecology by using isotopic (geochemical element) samples from both dental and bone material, which has never been studied before in thalattosuchians. Isotopes are an important component of palaeontological research in that they offer insight into an animal’s diet, growth, palaeoenvironment and habitat preference. The main objectives of this project include: (1) evaluating the specifics of thalattosuchian diet(s) through ontogeny (juvenile vs. adult of an individual species) and species, using calcium (Ca), nitrogen and carbon (C); (2) investigating habitat preference(s) within thalattosuchians, using strontium (Sr) and oxygen (O); and (3) examining migratory patterns in the thalattosuchian species Macrospondylus bollensis, using oxygen (O). We hypothesize that the isotopic data will support the following hypotheses: (1) in terms of diet, (i) juvenile thalattosuchians preferring invertebrates and small fish and adults favoring reptiles, large fishes and squid, (ii) Mystriosaurus favoring harder prey in comparison with other thalattosuchians, and (iii) smaller teleosauroids and Pelagosaurus will overlap in prey preference; (2) Platysuchus will favor a more freshwater/semiterrestrial environment and Macrospondylus will prefer a different area of the oceanic water column than other thalattosuchians; and (3) Macrospondylus juveniles will favor nearshore zones whereas adults will prefer offshore zones and display annual migration patterns (similar to modern crocodylians). These hypotheses are based on both morphological features and extant analogs. State of the art isotopic equipment will be used to guarantee the success of the project. These objectives are key to understanding thalattosuchian biology and ultimately how they became so successful early on in their evolution as top predators in the Posidonia Sea.

• DFG Programme: Research Grants
• Co-Investigator: Professor Dr. Thomas Tütken