Periodic Reporting for period 4 - VERTEBRATE HERBIVORY (Evolution of herbivory in vertebrates: developing combined isotope (Ca, Sr) and dental surface texture analysis as deep time diet proxies)
Okres sprawozdawczy: 2021-03-01 do 2022-12-31
The goal of the VERTEBRATE HERBIVORY was to develop new dietary proxies to ultimately constrain the evolution of herbivory (plant-feeding) and trophic interaction of extinct vertebrates at different spatiotemporal scales in past food webs by analysing their fossil teeth with isotopic and dental wear techniques. Different diets leave characteristic chemical and mechanical signatures in dental hard tissues or wear traces on tooth surfaces, respectively. The isotopic composition of tooth enamel records information about an animal’s diet over months-years, while wear features on the tooth surface track short-term food abrasion of only a few weeks, which reflects the mechanical food properties of the last meals eaten. Both, Ca and stable Sr isotopes decrease systematically along the food chain with each trophic level because the consumption of isotopically light bone leads to lower isotope ratios in carnivores than in herbivores. This enables us to reconstruct the diet and trophic level of extinct vertebrates and transitions from animal- to plant-feeding during ontogeny and evolutionary adaptations. A new approach using combined stable Ca and Sr isotopes as well as 3D dental surface texture (3DST) analysis was developed and applied to fossil teeth of mammal-ancestors and dinosaurs to reconstruct their diet and to identify early plant-feeders on land.
To broaden the versatility of the dietary toolbox, additional new isotopic diet and trophic level proxies such as Zn isotopes and N isotopes in enamel-bound organic matter were explored and validated on teeth from controlled feeding experiments and then for successfully applied to fossil teeth. For instance, Zn isotopes were used as trophic level proxy to assess the feeding ecology of the oldest anatomical modern human from SE Asia and its sympatric fauna, to trace a meat-rich diet of Neanderthals as well as to shed new light on potential food competition of the great white shark with the extinct Megalodon shark. Enamel-bound nitrogen isotopes display a similar trophic level effect of ca. 3-4 permille both in controlled rodent feeding experiments as well as for large mammals from modern African ecosystems. Enamel-bound N isotopes record the same dietary information as collagen-bound N of the same individuals and these diet-related N isotope compositions can be preserved over geological time scales in fossil teeth of Cenozoic mammals and megalodon sharks and even Mesozoic dinosaurs.
Food processing wears down teeth, thus affecting tooth functionality and evolutionary success. Therefore, another dietary proxy system microwear texture analysis of teeth was further explored which characterizes tooth surface wear at the microscopic level, enabeling us to distinguish soft- and hard-object feeders but also more subtle dietary differences and seasonality. In controlled feeding experiments fundamental factors influencing dental wear such as different natural diets (fruits, insects, seeds, vertebrates), amount, size and type of external mineral abrasives, amount of phytoliths, plant matter hydration state as well as the time to form and overwrite a diet-related surface texture were systematically assessed. Furthermore, mechanical and chemical alteration experiments were pursued to test the resistance of diet-related surface textures against taphonomic processes such as fluvial transport, aeolian sediment impact or acidic attack. A first catalogue of badly preserved enamel surface textures was compiled and can help to identify alteration of diet-related dental wear by postmortem surface modifications due to taphonomic or anthropogenic (i.e. excavation, preparation or conservation) effects.