Engineering the rise of animals

Abstract

Bioturbation – the physical movement of sediment by organisms – is a powerful form of ecosystem engineering through which animals can influence seafloor sediment characteristics and control the distribution of habitable subsurface space. The emergence and proliferation of these behaviors during the Ediacaran-Cambrian transition (‘ECT’; ~550-538 Ma) is coincident with the establishment of ecosystems dominated by animals. As such, it is crucial to understand the deep-time evolution of ecosystem engineering as it relates to biotic drivers of this unique interval in Earth history. In this dissertation I explore the rise of bioturbation during the ECT through systematic and experimental lenses. I evaluate and name the earliest-known total group scalidophoran traces, cementing a Precambrian lineage for this animal group. I also re-evaluate the enigmatic fossil Archaeichnium haughtoni for the first time since the 1970s, establishing that the practice of burrow reinforcement was well established by the earliest Cambrian. Finally, I present an experimental framework for assessing the deep time impacts of Ediacaran-Cambrian bioturbators through observation of their modern analogues in similar environments, and in doing so determine that these analogue organisms may be responsible for one of the fossil record's most impactful trace fossils.