Stretched, mangled, and torn: Responses of the Ediacaran fossil Dickinsonia to variable forces

Geology ◽  
2019 ◽  
Vol 47 (11) ◽  
pp. 1049-1053 ◽  
Author(s):  
Scott D. Evans ◽  
Wei Huang ◽  
Jim G. Gehling ◽  
David Kisailus ◽  
Mary L. Droser
Keyword(s):  
Plastic Deformation ◽  
Fossil Record ◽  
South Australia ◽  
Ediacara Biota ◽  
Evolution Of Life ◽  
Biomechanical Responses ◽  
Biological Characters ◽  
Oxygen Requirements ◽  
Elastic And Plastic Deformation ◽  
Extinct Taxon

Abstract Dickinsonia is one of the oldest macroscopic metazoans in the fossil record. Determining the biological characters of this extinct taxon is critical to our understanding of the early evolution of life. Preservation of abundant specimens from the Ediacara Member (Rawnsley Quartzite), South Australia, in a variety of taphonomic states allows the unparalleled opportunity to compare the biomechanical responses of Dickinsonia tissue to various forces with those typical of modern organisms. Dickinsonia are found as lifted, transported, folded, rolled, ripped, and expanded or contracted individuals, while maintaining diagnostic morphology. This suite of characters indicates that Dickinsonia was composed of material that was flexible, difficult to rip, and capable of elastic and plastic deformation. While none of these traits are diagnostic of a single biomaterial component, we find many similarities with modern biopolymers, particularly collagen, keratin, and elastin. Maintenance of significant relief following complete tearing suggests that Dickinsonia was composed of relatively thick tissues, signifying higher oxygen requirements than previously hypothesized. The ability to be transported and still be preserved as recognizable fossils is unique amongst the Ediacara Biota and demonstrates that Dickinsonia was a taphonomic elite. Combined with discovery in multiple environmental settings, this indicates that the absence of Dickinsonia represents the likely extinction of this organism prior to the Nama assemblage, possibly due to a decrease in the global availability of oxygen in the latest Ediacaran.

scholarly journals BIOLOGICAL AND ECOLOGICAL INSIGHTS FROM THE PRESERVATIONAL VARIABILITY OF FUNISIA DOROTHEA, EDIACARA MEMBER, SOUTH AUSTRALIA

Palaios ◽  
2020 ◽  
Vol 35 (9) ◽  
pp. 359-376
Author(s):  
RACHEL L. SURPRENANT ◽  
JAMES G. GEHLING ◽  
MARY L. DROSER
Keyword(s):  
South Australia ◽  
Ecosystem Dynamics ◽  
Cambrian Explosion ◽  
Ediacara Biota ◽  
National Heritage ◽  
Evolution Of Life ◽  
Fossil Site ◽  
Life On Earth ◽  
Body Fossil

ABSTRACT The Ediacara Biota represents a turning point in the evolution of life on Earth, signifying the transition from single celled organisms to complex, community-forming macrobiota. The exceptional fossil record of the soft-bodied Ediacara Biota provides critical insight into the nature of this transition and into ecosystem dynamics leading up to the so-called “Cambrian Explosion”. However, the preservation of non-biomineralizing organisms in a diversity of lithologies goes hand-in-hand with considerable taphonomic complexity that often shrouds true paleoecological and paleobiological signatures. We address the nature of this taphonomic complexity within the fossiliferous sandstones of the Ediacara Member in South Australia. Utilizing the most fossiliferous outcropping of the Ediacara Member, located at the Nilpena Station National Heritage Ediacara Fossil Site, we conduct a focused, taxon-level biostratinomic characterization of the tubular organism Funisia dorothea. Funisia is the most abundant body fossil in the Ediacara Member, making the characterization of its preservational variability essential to the accurate interpretation of regional paleobiology and paleoecology. We describe remarkable biostratinomic complexity in all Funisia populations at Nilpena, identifying four distinct preservational variants of internal and external molds and four additional successive biostratinomic grades corresponding to loss of external characters. Synthesis of these observations identify the most robust preservational forms of Funisia for use in paleobiological interpretation and highlight the important impact that Funisia's high abundance had on regional paleoecology and on population-scale preservation in the Ediacara Member.

Ediacara growing pains: modular addition and development in Dickinsonia costata

Paleobiology ◽  
2021 ◽  
pp. 1-16
Author(s):  
Scott D. Evans ◽  
James G. Gehling ◽  
Douglas H. Erwin ◽  
Mary L. Droser
Keyword(s):  
Body Size ◽  
Fossil Record ◽  
South Australia ◽  
Growth Stages ◽  
Genetic Pathways ◽  
Morphogen Gradients ◽  
Ediacara Biota ◽  
Growing Pains ◽  
Competing Hypotheses ◽  
The Relationship

Abstract Constraining patterns of growth using directly observable and quantifiable characteristics can reveal a wealth of information regarding the biology of the Ediacara biota—the oldest macroscopic, complex community-forming organisms in the fossil record. However, these rely on individuals captured at an instant in time at various growth stages, and so different interpretations can be derived from the same material. Here we leverage newly discovered and well-preserved Dickinsonia costata Sprigg, 1947 from South Australia, combined with hundreds of previously described specimens, to test competing hypotheses for the location of module addition. We find considerable variation in the relationship between the total number of modules and body size that cannot be explained solely by expansion and contraction of individuals. Patterns derived assuming new modules differentiated at the anterior result in numerous examples in which the oldest module(s) must decrease in size with overall growth, potentially falsifying this hypothesis. Observed polarity as well as the consistent posterior location of defects and indentations support module formation at this end in D. costata. Regardless, changes in repeated units with growth share similarities with those regulated by morphogen gradients in metazoans today, suggesting that these genetic pathways were operating in Ediacaran animals.

scholarly journals Discovery of the oldest bilaterian from the Ediacaran of South Australia

2020 ◽  
Vol 117 (14) ◽  
pp. 7845-7850 ◽  
Author(s):  
Scott D. Evans ◽  
Ian V. Hughes ◽  
James G. Gehling ◽  
Mary L. Droser
Keyword(s):  
Fossil Record ◽  
Common Ancestor ◽  
South Australia ◽  
Trace Fossils ◽  
Last Common Ancestor ◽  
Ediacara Biota ◽  
Size And Morphology ◽  
Animal Communities ◽  
Critical Link ◽  
Anterior Posterior

Analysis of modern animals and Ediacaran trace fossils predicts that the oldest bilaterians were simple and small. Such organisms would be difficult to recognize in the fossil record, but should have been part of the Ediacara Biota, the earliest preserved macroscopic, complex animal communities. Here, we describeIkaria wariootiagen. et sp. nov. from the Ediacara Member, South Australia, a small, simple organism with anterior/posterior differentiation. We find that the size and morphology ofIkariamatch predictions for the progenitor of the trace fossilHelminthoidichnites—indicative of mobility and sediment displacement. In the Ediacara Member,Helminthoidichnitesoccurs stratigraphically below classic Ediacara body fossils. Together, these suggest thatIkariarepresents one of the oldest total group bilaterians identified from South Australia, with little deviation from the characters predicted for their last common ancestor. Further, these trace fossils persist into the Phanerozoic, providing a critical link between Ediacaran and Cambrian animals.

scholarly journals Biostratinomy of the Ediacara Member (Rawnsley Quartzite, South Australia): implications for depositional environments, ecology and biology of Ediacara organisms

2020 ◽  
Vol 10 (4) ◽  
pp. 20190100 ◽  
Author(s):  
Mary L. Droser ◽  
Lidya G. Tarhan ◽  
Scott D. Evans ◽  
Rachel L. Surprenant ◽  
James G. Gehling
Keyword(s):  
Fossil Record ◽  
South Australia ◽  
Depositional Environments ◽  
Bedding Planes ◽  
Ediacara Biota ◽  
National Heritage ◽  
Fossil Site ◽  
Fossil Assemblages ◽  
Multicellular Organisms

The Precambrian Ediacara Biota—Earth's earliest fossil record of communities of macroscopic, multicellular organisms—provides critical insights into the emergence of complex life on our planet. Excavation and reconstruction of nearly 300 m 2 of fossiliferous bedding planes in the Ediacara Member of the Rawnsley Quartzite, at the National Heritage Ediacara fossil site Nilpena in South Australia, have permitted detailed study of the sedimentology, taphonomy and palaeoecology of Ediacara fossil assemblages. Characterization of Ediacara macrofossils and textured organic surfaces at the scale of facies, bedding planes and individual specimens has yielded unprecedented insight into the manner in which the palaeoenvironmental settings inhabited by Ediacara communities—particularly hydrodynamic conditions—influenced the aut- and synecology of Ediacara organisms, as well as the morphology and assemblage composition of Ediacara fossils. Here, we describe the manner in which environmental processes mediated the development of taphofacies hosting Ediacara fossil assemblages. Using two of the most common Ediacara Member fossils, Arborea and Dickinsonia , as examples, we delineate criteria that can be used to distinguish between ecological, environmental and biostratinomic signals and reconstruct how interactions between these processes have distinctively shaped the Ediacara fossil record.

Scratch Traces of Large Ediacara Bilaterian Animals

2014 ◽  
Vol 88 (2) ◽  
pp. 284-298 ◽  
Author(s):  
James G. Gehling ◽  
Bruce N. Runnegar ◽  
Mary L. Droser
Keyword(s):  
Fossil Record ◽  
Microbial Mats ◽  
White Sea ◽  
South Australia ◽  
Trace Fossil ◽  
Cambrian Explosion ◽  
The White Sea ◽  
Feeding Patterns ◽  
Fossil Evidence ◽  
Ediacara Biota

Ediacara fan-shaped sets of paired scratchesKimberichnus teruzziifrom the Ediacara Member of the Rawnsley Quartzite, South Australia, and the White Sea region of Russia, represent the earliest known evidence in the fossil record of feeding traces associated with the responsible bilaterian organism. These feeding patterns exclude arthropod makers and point to the systematic feeding excavation of seafloor microbial mats by large bilaterians of molluscan grade. Since the scratch traces were made into microbial mats, animals could crawl over previous traces without disturbing them. The trace maker is identified asKimberella quadrata, whose death masks co-occur with the mat excavation traces in both Russia and South Australia. The co-occurrence of animals and their systematic feeding traces in the record of the Ediacara biota supports previous trace fossil evidence that bilaterians existed globally before the Cambrian explosion of life in the ocean.

Deformation, Fracture, and Friction Processes

2020 ◽  
pp. 14-24
Author(s):  
Francois Louchet
Keyword(s):  
Plastic Deformation ◽  
Ductile Failure ◽  
Scientific Validity ◽  
Coulomb’S Friction ◽  
Dynamic Loadings ◽  
Triggering Mechanisms ◽  
The Difference ◽  
Elastic And Plastic Deformation ◽  
Physical Quantities ◽  
Rupture Criterion

The main mechanical and physical quantities and concepts ruling deformation, fracture, and friction processes are recalled, with particular attention paid to the simplicity of the analysis, but without betraying the scientific validity of the arguments. We particularly discuss the difference between between elastic and plastic deformation, and quasistatic and dynamic loadings, essential in avalanche triggering mechanisms. The physical origin of Griffith’s rupture criterion that rules both fracture nucleation and propagation, and the transition between brittle and ductile failure processes, is thoroughly discussed. We also explain the physical meaning of the classical Coulomb’s friction law, showing why it can hardly apply to a non-conventional porous, brittle, and healable solid like snow.

Paleometry as a key tool to deal with paleobiological and astrobiological issues: some contributions and reflections on the Brazilian fossil record

2019 ◽  
Vol 18 (6) ◽  
pp. 575-589 ◽  
Author(s):  
Amanda L. S. Gomes ◽  
Bruno Becker-Kerber ◽  
Gabriel L. Osés ◽  
Gustavo Prado ◽  
Pedro Becker Kerber ◽  
...  
Keyword(s):  
Fossil Record ◽  
Microbial Mats ◽  
Fish Bone ◽  
Common Interest ◽  
Cross Point ◽  
Origin And Evolution ◽  
Evolution Of Life ◽  
Bone Preservation ◽  
Fossil Preservation ◽  
Non Destructive

AbstractInvestigations into the existence of life in other parts of the cosmos find strong parallels with studies of the origin and evolution of life on our own planet. In this way, astrobiology and paleobiology are married by their common interest in disentangling the interconnections between life and the surrounding environment. In this way, a cross-point of both sciences is paleometry, which involves a myriad of imaging and geochemical techniques, usually non-destructive, applied to the investigation of the fossil record. In the last decades, paleometry has benefited from an unprecedented technological improvement, thus solving old questions and raising new ones. This advance has been paralleled by conceptual approaches and discoveries fuelled by technological evolution in astrobiological research. In this context, we present some new data and review recent advances on the employment of paleometry to investigations on paleobiology and astrobiology in Brazil in areas such biosignatures in Ediacaran microbial mats, biogenicity tests on enigmatic Ediacaran structures, research on Ediacaran metazoan biomineralization, fossil preservation in Cretaceous insects and fish, and finally the experimental study on the decay of fish to test the effect of distinct types of sediment on soft-tissue preservation, as well as the effects of early diagenesis on fish bone preservation.

Ediacaran scavenging as a prelude to predation

2018 ◽  
Vol 2 (2) ◽  
pp. 213-222 ◽  
Author(s):  
James G. Gehling ◽  
Mary L. Droser
Keyword(s):  
Microbial Mats ◽  
South Australia ◽  
Trace Fossil ◽  
Localized Source ◽  
Oxygen Levels ◽  
Stem Group ◽  
Ediacara Biota ◽  
Ecological Innovation ◽  
Large Predators ◽  
Ancient Ecosystems

Predation is one of the most fundamental ecological and evolutionary drivers in modern and ancient ecosystems. Here, we report the discovery of evidence of the oldest scavenging of shallowly buried bodies of iconic soft-bodied members of the Ediacara Biota by cryptic seafloor mat-burrowing animals that produced the furrow and levee trace fossil, Helminthoidichnites isp. These mat-burrowers were probably omnivorous, stem-group bilaterians that largely grazed on microbial mats but when following mats under thin sands, they actively scavenged buried Dickinsonia, Aspidella, Funisia and other elements of the Ediacara Biota. These traces of opportunistic scavengers of dead animals from the Ediacaran of South Australia represent a fundamental ecological innovation and a possible pathway to the evolution of macrophagous predation in the Cambrian. While the Ediacaran oceans may have had oxygen levels too low to support typical large predators, the Helminthoidichnites maker lived in and grazed on microbial mats, which may have provided a localized source of oxygen.

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