Orsten-type fossils from the Ordovician and the early diversification of tongue-worm-like parasites: quantitative morphology and inner anatomy

• Applicants: Professor Dr. Joachim Tobias Haug; Professor Dr. Alexander Nützel
• Subject Area: Palaeontology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 548956903

Though biological interactions of animals are mostly envisaged as predator-prey relationships, it is in fact the parasite-host interactions that seem to be the more common and possibly the more important ones regarding the evolutionary and ecological impact. It has been estimated that 50% of all living animal species are parasitic, and the evolution of parasitism is seen as a major driver for diversification. Furthermore, parasitism concerns human health as parasites cause severe illnesses to humans, and also the economical impact of parasites, for example on livestock or also on crop plants, is enormous. Especially parasites in the group Arthropoda play an important role, for example, mites or different species of Insecta. Our understanding of parasitism can strongly benefit from investigating parasites or their traces in the fossil record, which are in fact not as rare as one might expect. The oldest fossil parasitic forms of Arthropoda, usually interpreted as representatives of tongue worms, have been identified from the upper Cambrian of Sweden and are very well preserved (Orsten-type). Similar fossils from the Ordovician of Sweden are even better preserved, with internal anatomy such as muscle fibres, unknown from the Cambrian fossils. In this project, the diversity between Cambrian and Ordovician tongue-worm-like fossils will be compared (especially as this is the time of the Great Ordovician Biodiversification Event = GOBE), as well as with that of extant forms. Also possible ontogenetic changes will be investigated. These comparisons will be based on quantitative morphology data. Quantitative morphology is a set of tools that allows to quantify morphological traits, in this case shapes of morphological structures (whole body, head, claws). As quantified shapes represent a proxy for functional aspects, i.e., certain morphologies in extant forms are coupled to specific functions (e.g. areas of host attachment), this allows to draw conclusions for fossils concerning such aspects of functional morphology. We will also compare details of the inner anatomy, especially of the muscular arrangement, of the Ordovician tongue-worm-like fossils with those in possible modern relatives by using thin sectioning as well as µCT scanning and serial blockface imaging. Similarities in this arrangement may point to a closer relationship. Also comparisons with the arrangement in fish lice (Branchiura) will be performed, which have been suggested to be close relatives of modern tongue worms. The musculature may additionally give hints to the type of attachment of the fossils, e.g. if they were ectoparasites. Our results will provide important new insights on the evolution of tongue worms and parasitism in general.

• DFG Programme: Research Grants