Research

Although we study organism-environment interactions throughout Earth’s history, a major arm of our research program is particularly focused on the Neoproterozoic–early Paleozoic—the interval of time in which complex animal communities appeared and began to shape, and were shaped by, the environments they inhabited. This interval of Earth’s history is also unique for the remarkable frequency of fossil deposits characterized by exceptional preservation of soft tissues, and the variety of pathways by which these tissues are fossilized. Below are descriptions of three of our major areas of ongoing research.

Ediacaran Paleoecology, Paleoenvironments and Preservation
The Ediacara Biota, Earth’s earliest macroscopic, multicellular communities—which appeared in the fossil record just prior to the Cambrian Explosion—holds the key to reconstructing the evolution and radiation of complex life on this planet. Understanding the taphonomy (postmortem preservational processes) and diagenetic history of these deposits is an essential prerequisite to unraveling the habitat, paleoecology and phylogenetic relationships of early complex life and distinguishing genuine evolutionary signals from preservational artefacts (Droser et al., 2020, Interface Focus; Tarhan et al., 2015, Precambrian Research; Tarhan et al., 2010, Palaios). Our work has also recently focused on the mechanisms responsible for ‘Ediacara-style’ preservation (the paradoxical exceptional fossilization of soft-bodied organisms as three-dimensional casts and molds in sandstones). Using petrographic and geochemical (e.g., laser ablation ICP-MS, microprobe-based SEM-EDS and cathodoluminescence microscopy), as well as paleontological data, we demonstrated that early-precipitating silica cements, sourced from oceans rich in dissolved silica prior to the evolution of silica-biomineralizers, were responsible for Ediacara-style preservation in the Ediacara Member of South Australia—the ‘type’ deposit of the Ediacara Biota (Tarhan et al., 2016, Geology). We have also used experimental approaches to demonstrate that at a molecular level Ediacara-style fossilization is mediated by the density of particular organic functional groups in animal tissues and bacterial cells reactive to dissolved silica (Slagter et al., 2021). We also study the sedimentary record of Ediacaran matgrounds, in order to determine how prolific and diverse organically bound seafloor sediments shaped the ecology and environmental interactions of Ediacara communities, as well as their fossilization (Tarhan et al., 2022, Precambrian Research; Tarhan et al., 2018, Integrative and Comparative Biology; Tarhan et al., 2017, Palaios; Droser et al., 2017, Annual Reviews in Earth and Planetary Sciences; Tarhan et al., 2010, Palaios). We have investigated the paleoecology and taphonomy of upper Ediacaran and lower Cambrian ‘tubular’ fossils—multicellular organisms with tube-shaped bodies and of largely cryptic affinities that are common in Ediacaran–Cambrian fossil assemblages—at various sites around the world, including South Australia (Tarhan et al., 2018, Integrative and Comparative Biology; Tarhan et al., 2015, Precambrian Research), the Death Valley and White-Inyo regions of the western USA, and the Lesser Himalaya of India (Tarhan et al., 2014, Palaeontology). More broadly, we are interested in the interplay between extinction, environmental perturbation and fossil preservation across the Precambrian-Cambrian boundary (Tarhan et al., 2018, Integrative and Comparative Biology; Droser et al., 2017, Annual Reviews in Earth and Planetary Sciences). Using a sedimentological, geobiological and geochemical toolkit, we also have been reconstructing the environmental setting and habitat of the Ediacara Biota (Fakhraee et al., 2021, PNAS; Tarhan et al., 2018, Geobiology; Tarhan et al., 2015, Palaeo-3), as well as addressing the question of to what extent changes in oxygenation paved the way for the Cambrian Explosion of complex animal body plans and ecologies (Wei et al., 2020, EPSL; Wei et al., 2018, Geology; Li et al., 2015, Scientific Reports). Detailed and field-based paleoenvironmental work is crucial to tracking the emergence of environments hospitable to complex life, and to determining how environmental changes may have shaped the appearance and radiation of animals, as well as the nature of the Ediacaran–Cambrian fossil record.

Excavation sites, where pieces of the Ediacaran seafloor are discovered and reassembled.
Excavating and reconstructing beds at the Nilpena National Heritage Site, South Australia.
Once beds are pieced back together, the paleoecology and taphonomy of the fossilized communities and the sedimentology of the sandstone beds hosting them are logged and described in detail.
Fossils of the Ediacara Biota of South Australia.
Tarhan et al., 2016, Geology
Ediacaran matgrounds and trace fossils.
Droser et al., 2017, Annual Review of Earth and Planetary Sciences
Detailed field-based sedimentology and paleoecology, coupled with a better understanding of fossilization mechanisms, allow us to reconstruct ancient community structure and track how this changed through the Ediacaran Period.
Droser et al., 2017, Annual Review of Earth and Planetary Sciences
The presence of microbial mats changed the sedimentology and stratigraphic packaging of Ediacara fossil deposits. Tarhan et al., 2017, Palaios