Taphonomic and mass-extinction research from an ichnological perspective.

Abstract

The assemblage of Pleistocene megafauna at Waco Mammoth National Monument (WMNM) and the terrestrial Cretaceous-Paleogene (K-Pg) boundary at Big Bend National Park are just two examples that demonstrate the peril effects of an extreme environmental perturbation on ancient ecosystems. Ichnology is the study of traces that are generated by organismal behavior; therefore, analyzing major die-offs through an ichnological lens can provide a unique perspective to understand the ethology of the survivors. At WMNM trace-fossil analysis was combined with taphonomy, which revealed that the Columbian mammoth herd was subjected to extensive vertebrate and invertebrate scavenging. These findings necessitated a re-evaluation of the causal mechanisms responsible for the death of the herd, as well as demonstrated that scavenging organisms out-survived, at least for some time, the large herbivores in this case. The application of ichnology to the terrestrial K-Pg boundary revealed new findings about the surviving organisms in response to the end-Cretaceous extinction. Herbivorous, soil-dwelling insects, as evidenced from analogous traces, were significantly reduced in body size (Lilliput effect) following the aftermath of the event. These findings, in conjunction with research on marine-organism responses, provide empirical evidence that the Lilliput effect was a phenomenon that affected surviving organisms across highly disparate trophic levels and ecosystems. Lastly, a hybrid approach of ichnology and zooarchaeology was used to develop morphological criteria for taphonomic analysts to differentiate between carnivore traces and unintentional, preparator air-scribe marks, which can be more similar than one might imagine. Utilization of an ichnological perspective to study survival behaviors from the ancient past may one day help address some of the decisions regarding our current mass extinction.