The role of iron in the formation of Ediacaran ‘death masks’

Abstract

The Ediacara biota are an enigmatic group of Neoproterozoic soft‐bodied fossils that mark the first major radiation of complex eukaryotic and macroscopic life. These fossils are thought to have been preserved via pyritic “death masks” mediated by seafloor microbial mats, though little about the chemical constraints of this preservational pathway is known, in particular surrounding the role of bioavailable iron in death mask formation and preservational fidelity. In this study, we perform decay experiments on both diploblastic and triploblastic animals under a range of simulated sedimentary iron concentrations, in order to characterize the role of iron in the preservation of Ediacaran organisms. After 28 days of decay, we demonstrate the first convincing “death masks” produced under experimental laboratory conditions composed of iron sulfide and probable oxide veneers. Moreover, our results demonstrate that the abundance of iron in experiments is not the sole control on death mask formation, but also tissue histology and the availability of nucleation sites. This illustrates that Ediacaran preservation via microbial death masks need not be a “perfect storm” of paleoenvironmental porewater and sediment chemistry, but instead can occur under a range of conditions.

Causes and consequences of end-Ediacaran extinction – an update

“…Our understanding of the geochronology, chemostratigraphy, and biostratigraphy of the late Ediacaran has increased substantially in the last 10 years. However, given uncertainties surrounding stratigraphic correlation between sites (Xiao et al, 2016), the placement of key boundaries (Nelson et al, 2022), and the mechanisms of fossil preservation (Laflamme et al, 2013;Slagter et al, 2022;Gibson et al, 2023), a reasonable question is: do these apparent intervals of biotic turnover really represent extinction intervals (or more specifically, 'mass' extinctions) at all? The iconic Ediacaran fossil sites in South Australia illustrate some of these issues; they are among the best-studied Ediacaran localities, are frequently taken to epitomize the diversity and community structure of Lastly, many Ediacara biota may have also had important ecosystem engineering impacts; the enigmatic taxa Ernietta (J), Arkarua (H; sp.…”

Taphonomic experiments fixed and conserved with Paraloid B72 resin via solvent replacement

“…dissolved silica; Slagter et al 2021). Conversely, more realistic approaches that attempt to replicate the conditions experienced by carcasses during fossilization acknowledge the complexity of the processes associated with preservation and decay (Darroch et al 2012;Gibson et al 2018Gibson et al , 2023, but can struggle to distinguish the roles of individual variables in taphonomic processes. Other experiments are simply permitted to occur in modern-day environments (White & Diedrich 2012), since taphonomic processes such as hyaena scavenging may be best-replicated in natural settings, without human intervention.…”

“…Taphonomic experiments employed to test the feasibility of some of these competing taphonomic models either attempt to replicate presumed Ediacaran burial conditions to produce Ediacaran-style preservation of modern analogue organisms (Darroch et al 2012;Gibson et al 2018Gibson et al , 2023, or seek to constrain the range of environmental conditions under which a specific preservational model is viable (Slagter et al 2021(Slagter et al , 2022. Such decay experiments typically fall into one of two categories, distinguished by precisely how they observe the experimental products: those that examine mineralization, or character loss, in vitro (Slagter et al 2021(Slagter et al , 2022; or those that exhume the carcass from sediment post-burial and decay (Darroch et al 2012;Gibson et al 2018Gibson et al , 2023.…”

“…Taphonomic experiments employed to test the feasibility of some of these competing taphonomic models either attempt to replicate presumed Ediacaran burial conditions to produce Ediacaran-style preservation of modern analogue organisms (Darroch et al 2012;Gibson et al 2018Gibson et al , 2023, or seek to constrain the range of environmental conditions under which a specific preservational model is viable (Slagter et al 2021(Slagter et al , 2022. Such decay experiments typically fall into one of two categories, distinguished by precisely how they observe the experimental products: those that examine mineralization, or character loss, in vitro (Slagter et al 2021(Slagter et al , 2022; or those that exhume the carcass from sediment post-burial and decay (Darroch et al 2012;Gibson et al 2018Gibson et al , 2023. Examination in vitro permits the real-time, direct observation of authigenic mineral growth on the surfaces of carcasses (Briggs et al 1993;Slagter et al 2021Slagter et al , 2022, the sequence of character loss during decay (Sansom et al 2010;Murdock et al 2014;McMahon et al 2017;Hancy & Antcliffe 2020), microbial growth dynamics (Butler et al 2015;Iniesto et al 2017), and relative tissue recalcitrance (Slater et al 2021).…”

“…Although experimental burial within sediment is considered to reflect more realistic decay conditions in the vicinity of the carcass, this requires the inclusion of media (e.g. plastic sheets) within the experimental substrate to permit separation of sediment along the plane of the carcass (Darroch et al 2012;Gibson et al 2018Gibson et al , 2023, and risks disarticulation or disruption of the carcass (e.g. during manipulation; Iniesto et al 2017), and displacement of the delicate authigenic phases under investigation.…”