VANISHED WITH A TRACE: ICHNOLOGICAL APPLICATIONS TO EXTINCTION-RECOVERY RESEARCH

Applications of trace fossil (ichnological) datasets to mass-extinction research has the key advantage of in situ context of traces of extinct taxa (Last Appearance Datum) in addition to traditional benefits, such as the record of soft-bodied organisms, diagenetic enhancement, and occurrence in lithologies and environments with poor preservation of skeletal remains. In contrast to some instances of time-transgressive occurrence in older sediments (e.g., deep track and root penetration through paraconformities), no traces of extinct biota occur in younger strata (cf. Lazarus species). On the other hand, (semi)fossorial lifestyle is increasingly viewed as one of the key strategies for surviving extinctions in both marine and continental settings. Burrows may preferentially preserve impact-related indicators and, similar to event-triggered lithological anomalies on paleo-surfaces (e.g., post-storm density lag along coastlines), ash from volcanic eruptions may serve as a suitable tracking medium. Building on a growing database, we present examples of recent ichnological studies: 1) evidence for a hydroclimatically forced increase in diversity of terrestrial vs. aquatic communities across the Permian-Triassic boundary in high latitude ecosystems (Antarctica); 2) mid-shelf positive endobenthic feedback followed by a 20­–30% burrow diameter (~body size) reduction in response to the K-Pg event (Western North Atlantic seaboard); 3) substantial decrease (40­–50%) in mammalian and invertebrate burrow diameters in response to transient environmental and climatic perturbations associated with the Paleocene-Eocene Thermal Maximum (Wyoming); and 4) ichnological and taphonomic evidence for mass mortality of Pleistocene megafauna (Texas). Finally, we will address the current lack of ichnological evidence for less dramatic extinction events (including historical times), which nevertheless involve the world’s largest representatives of chelonians, as well as terrestrial birds and mammals.