Local diversities and predation: Eocene to Recent

The most striking feature of life on Earth is its diversity. Predation is one of the most important agents of the natural selection behind this diversity and various types of traces on fossil skeletons indicate predator-prey interactions throughout the history of life. It is therefore particularly appealing to link studies on biodiversity in the fossil record with studies on traces of predation. The focus in this project will be on predatory drill holes (mostly from naticid and muricid gastropods), which are probably the most frequently used indicators of invertebrate predator-prey interactions in Recent and fossil marine ecosystems. The large-scale (global or long-term) relationship between predation and morphological change is well established, but more fine-scale studies from the fossil record are needed, including comparisons with modern ecological studies, to evaluate spatial variability and patchiness of diversity patterns and traces of predation. Studying local palaeoecological patterns requires reliable databases of local assemblages; the primary concern with studying fine-scale processes in the fossil record is overcoming taphonomic biases. For this purpose we can rely on available bulk samples from the Eocene to the Recent (a time of stable, high predation intensities). These samples provide quantitative data of highest quality with detailed stratigraphic, palaeoenvironmental and taphonomic informations, based on extensive fieldwork of the project applicants or their national and international co-workers. Some additional sampling is planned to improve the database. The taxonomic resolution is mostly at the species level. We plan to gather assemblage-level palaeoeecological data and to trace species and clades through time in physically similar habitats. Diversity will be measured as species richness and evenness. The values will be compared between samples and localities using species accumulation- and rarefaction curves. Patterns of drilling predation will be determined by analysing predation intensity, analysing different types of selectivity, and testing for taphonomic biases. The results of the project will improve our knowledge about the spatial variability and patchiness of diversity patterns and traces of predation, about the taphonomic influences on these palaeoecological features, and they will contribute to formulating generalizations about the influence of predation on specific lineages and palaeocommunities. The project results will also contribute closing the gap between the global, deep-time scales of palaeobiology and the fine spatial and temporal scales typical of ecology and conservation.

We studied diversities, faunal gradients and drilling intensities (a measure and proxy of predation pressure in the fossil record) of shelly fossil marine animals. Our work considered mostly molluscs but also brachiopods from several European regions and different time-slices, including the Pyrenees (Eocene), Paris Basin (Eocene), Aquitan Basin (Oligocene, Miocene), Paratethys (Miocene), Tuscany and Emilia Romagna (Pliocene and Pleistocene). In addition we studied marine animals from the modern Adriatic Sea and Red Sea as warm-temperate and subtropical-tropical equivalents to our fossils. Much of our work consisted of building databases on species- abundances of samples from the above basins and of evaluating corresponding predation intensities. For the modern northern Adriatic Sea drilling frequency is relatively high in subtidal environments, falsifying previous hypotheses, but it does not seem to control diversity at this local scale. In a regional-scale study in the Miocene of the Central Paratethys a major diversity change between two regional time-slices is driven by strong changes in environments and molluscan assemblages from both time-slices are developed along the same environmental gradient. At the level of time-slices, environments and localities, drilling frequencies were always distinctly lower here than in other Miocene seas. In a methodological study the samples from the Eocene Paris Basin consistently had a much higher diversity than those of the Miocene of the Paratethys and the choice of sieve sizes strongly influenced diversity results from both regions. In contrast to the Paris Basin, however, Miocene drilling frequencies also differed significantly between size categories. Eocene deeper subtidal communities from the Pyrenees and the Paris Basin had a very high diversity and were dominated by the same families as those of the Pliocene of Tuskany and Emilia Romagna. The distribution of mollusc families in intertidal and shallow subtidal settings, however, shows significant differences, which we tentatively attribute to the decrease of mangroves and the rise of benthic primary producers, most notably diatoms, during the Cenozoic. Brachiopods in shallow-water environments of the northern Red Sea are restricted to cryptic habitats under coral colonies, but even there they contribute only few percent to the sediment composition. Analyses of brachiopod preservation from these subtropical carbonate environments, covering shallow coral habitats down to a 1500-m deep basin showed that drilling intensities decreased slightly with depth and that the negative role of shell organic content for preservation is overridden by shell thickness. Environmental sensitivity of preservation states is driven by present-day variation in environment but also by past Pleistocene conditions. Finally, 180 species of gastropods from the northern Red Sea are taxonomically investigated and provided with detailed environmental information.