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)
Periodo di rendicontazione: 2021-03-01 al 2022-12-31
Food is a major factor driving the evolution of vertebrates. In the last 300 million years, herbivory (plant-eating) evolved multiple-times from meat- or insect-feeders, first among synapsids (mammal-ancestors), then dinosaurs and later hominids as well. However, our understanding of when and in which species herbivory evolved is incomplete. This is because classical diet proxies such as rely on dental and skeletal morphology or bone chemistry often yield ambiguous results or are biased by fossilisation. To overcome these challenges new deep-time diet proxies, independent of tooth shape and species, that are also resistant to diagenetic alteration are needed.
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.
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.
Ca isotope and dental microwear texture proxies were calibrated on teeth of extant vertebrates with known plant- and animal-based natural as well as custom-made diets. For this purpose animals (rats, guinea pigs, quails and iguanas) were raised in controlled feeding experiments also designed to simulate diet and trophic level switches and also wild animals with well-constrained feeding ecology from modern ecosystems were analyzed. The diet-to-bioapatite Ca isotope fractionation of dental tissues and bone was determined for different mammal, bird and reptile taxa fed the same distinct plant-, meat-, and insect-based pelleted diets. It seems to be similar across different vertebrate taxa, which permits an application to fossil and extinct taxa. Calcium and stable strontium isotopes enable us to distinguish both meat- and insect-feeders from plant-feeders. Diet-related Ca isotopes and enamel surface textures both have a high preservation potential in fossil teeth, which was confirmed by chemical and mechanical in vitro alteration experiments. Moreover, these methods facilitate minimal-invasive micro-sampling of enamel for Ca isotope and non-destructive 3DST analysis of teeth which is even applicable to a single tooth. For the first time, Ca isotope and 3DST analysis were combined to reconstruct the diet of extinct vertebrate taxa and their trophic level in fossil food webs. In Permo-Carboniferous food webs comprising the earliest presumed herbivores such as edaphosaurids, diadectomorphs and casaeids higher Ca isotope signatures in their bones and teeth were measured than for sympatric carnivorous pelycosaurs such as Dimetrodon or sphenacodontids, which is in line with herbivory of the former. This confirms that the first transition from animal- to plant-feeding among terrestrial tetrapods occurred around 300 million years ago or even earlier.
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.
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.
The new multi-proxy approach will provide a versatile toolbox to test morphology-based feeding hypotheses, leading to important new insights into the palaeoecology, dietary flexibility and niche partitioning of fossil vertebrates. The combined analysis of different non-traditional isotopes such as Ca, Zn and N in enamel yield dietary information on the amount of bone, meat or protein consumption, respectively. While dental microwear texture analysis tracks differences in mechanical ingesta properties and chewing mechanics. Altogether, this toolbox will enable a more refined and quantitative reconstruction of the diet and feeding ecology of vertebrates beyond the state of the art and their trophic interaction in fossil food webs. Beyond the field of palaeontology these dietary proxies will be broadly applicable in archaeology, anthropology and ecology. Exploring dietary traits and trophic relationships both in modern and fossil food webs is fundamental for a better understanding of ecosystem resilience, the inner workings of food webs as well as radiation and extinction events but may also provide new insights into the dietary habits and evolution of vertebrates, including our human ancestors.