Potential and problems in evaluating secular changes in diversity of animal‐substrate interactions at ichnospecies rank

Changes in diversity of trace fossils through time provide information about evolutionary innovations in animal-substrate interactions. Global ichnodiversity changes at ichnogeneric rank are useful to capture major trends, but may be insufficient to reveal minor behavioural innovations. A quantitative analysis of ichnodiversity trajectories at ichnospecies rank for bioturbation structures has been performed for the first time at a global scale to evaluate how innovations in animal-substrate interactions may be reflected at this ichnotaxonomic hierarchy. The timing of diversification at ichnospecific rank is highly variable, but mostly linked to the Cambrian Explosion (CE) and the Mesozoic Marine Revolution (MMR). Nearly all top-heavy ichnogenera diversified during the MMR, and most bottom-heavy ichnogenera illustrate innovations during the CE. Timing of diversification at ichnospecies rank refines characterization of the ichnological equivalents of the Cambrian, Palaeozoic and Modern evolutionary fauna. Evaluating the timing of ichnospecific diversification within ichnogenera is a valuable tool in evolutionary palaeoecology.