Biofilms as agents of Ediacara-style fossilization

Abstract

Earth’s earliest fossils of complex macroscopic life are recorded in Ediacaran-aged siliciclastic deposits as exceptionally well-preserved three-dimensional casts and molds, known as “Ediacara-style” preservation. Ediacara-style fossil assemblages commonly include both macrofossils of the enigmatic Ediacara Biota and associated textural impressions attributed to microbial matgrounds that were integral to the ecology of Ediacara communities. Here, we use an experimental approach to interrogate to what extent the presence of mat-forming microorganisms was likewise critical to the Ediacara-style fossilization of these soft-bodied organisms. We find evidence that biofilms can play an instrumental role in fostering fossilization. Rapid silica precipitation associated with macroorganism tissues is enhanced in the presence of mat- and biofilm-forming microorganisms. These results indicate that the occurrence of microbial mats and biofilms may have strongly shaped the preservational window for Ediacara-style fossils associated with early diagenetic silica cements, and therefore influenced the distribution and palaeoecological interpretation of the Ediacara Biota fossil record.

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

“…Our results also demonstrate that the death mask model is not restricted to pyrite alone and could feasibly make use of other iron sulfide polymorphs that could mutually explain the presence of iron oxides and oxyhydroxides found in association with Ediacaran fossils (Liu, 2016; Liu et al, 2019). Previous work has suggested that microbial mats encourage (Slagter et al, 2022), but are not required for, Ediacaran preservation (Newman et al, 2019), demonstrating that this preservational pathway is pliable and thus able to occur under a larger variety of environmental conditions. Our results similarly suggest that this taphonomic pathway may not be as rigid as previously thought, ultimately not requiring a “perfect storm” of pore water microenvironmental and microbial substrate conditions, but instead possible under a wider variety of geochemical conditions and paleoenvironments.…”

Cellular structure of dinosaur scales reveals retention of reptile-type skin during the evolutionary transition to feathers

“…Recent experimental work has demonstrated that rapid and early silica precipitation can lead to soft tissue preservation within a short time frame postmortem 62 . Hydroxyl, amino and carboxyl groups common in decaying protein-rich tissues 32 can actively bind silicate ion species via hydrogen bonding, electrostatic interactions and cation bridging 62 , 84 . This process can proceed even at silica concentrations well below saturation, inducing rapid silica precipitation within 24 hours postmortem 62 , 84 .…”

“…Hydroxyl, amino and carboxyl groups common in decaying protein-rich tissues 32 can actively bind silicate ion species via hydrogen bonding, electrostatic interactions and cation bridging 62 , 84 . This process can proceed even at silica concentrations well below saturation, inducing rapid silica precipitation within 24 hours postmortem 62 , 84 . Given the likely high abundance of these functional groups in the tissue and the availability of dissolved silica, it is likely that silicification of the Psittacosaurus skin commenced quickly after arriving at the burial site.…”

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.…”