Swimming reptiles make their mark in the Early Triassic

This spike in swim track occurrences suggests that during the Early Triassic, factors promoting swim track production and preservation were more common than at any other time. Coincidentally, the Early Triassic period follows the largest mass extinction event in Earth's history, and the fossil record indicates that a prolonged period of delayed recovery persisted throughout this time period.

During this recovery interval, sediment mixing by animals living within the substrate was minimal, especially in particularly stressful environments such as marine deltas. The general lack of sediment mixing during the Early Triassic was the most important contributing factor to the widespread production of firm-ground substrates ideal for recording and preserving subaqueous trace fossils like swim tracks.