BIOTIC INTERACTIONS BETWEEN ANIMALS AND PLANTS IN BENTHIC MARINE ENVIRONMENTS DOMINATED BY ECHINOIDS AND CORALLINE RED ALGAE FROM THE MIOCENE OF SARDINIA (Invited Presentation)

Biotic interactions between animals and plants can be used to track the history of herbivory within the evolutionary context of predators (the herbivores) and prey (their plant food). Throughout their evolution, herbivorous echinoids have developed increasingly efficient tooth morphologies and associated jaw apparatus in order to access food resources in their benthic marine habitats leading to increased bioerosion, sediment production as well as potential shifts in the morphology of their soft and skeletonized prey.

In this study, biotic interactions between echinoids and coralline red algae are assessed within well preserved fossil assemblages from the Early Miocene of Sardinia. Sublittoral successions have preserved not only soft substrate assemblages (dominated by spatangoids) but also hard substrates represented by rhodolith beds containing associated regular sea urchin faunas. The excellent preservation of the echinoid skeletons allows for detailed functional morphological interpretations especially upon comparison to recent faunas. The rhodoliths are analyzed with respect to coralline taxonomic diversity, size and sphericity, growth forms and associated bioinfestation including both additional encrusters and bioerosion traces.

The size and complexity of the rhodoliths including extensive encrustation sequences and intense bioturbation indicate long surface residence times within the photic zone. The spheroidal to subspheroidal rhodoliths include not only the dominating coralline algae but also encrusting acervulinid foraminifera, corals as well as barnacles and bryozoans. The rhodolith show growth forms ranging from densely encrusting to fruticose thalli. The associated echinoids consist of tests, spines and test fragments of diadematoids, cidaroids as well as camarodonts among the regular echinoids. The extent to which these epibenthic grazing echinoids influence coralline algal presence and morphology is discussed with respect to substrate preferences and the evolution of tooth and jaw morphologies.