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.

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.

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.

Fringe political parties or political parties at the fringes? The dynamics of political competition in post-communist Europe

2019 ◽  
pp. 135406881986362 ◽  
Author(s):  
Sergiu Gherghina ◽  
Adam Fagan
Keyword(s):  
Political Parties ◽  
Political Competition ◽  
Special Issue ◽  
Growing Pains ◽  
Post Communism ◽  
Communist Countries ◽  
The Relationship

Much of the literature on fringe political parties in post-communist Europe focused on the relationship with mainstream parties. Little is known about what happens at the fringes, what are the features of politics at the fringes and when this type of politics becomes mainstream. This special issue moves beyond the notion of the fringe versus mainstream dichotomy: it is more ‘granular’ in its approach and seeks to differentiate between different forms of ‘fringe’ parties. The contributions aim to explore how and whether the fringe in post-communist countries changes in an age of populism and illiberalism. They represent an important attempt to take the fringe as a feature of politics that is not necessarily transient or a manifestation of the ‘growing pains’ of post-communism.

Leg Strength Is Related to Endurance Run Performance in Children and Adolescents with Mental Retardation

2000 ◽  
Vol 12 (3) ◽  
pp. 324-333 ◽  
Author(s):  
Bo Fernhall ◽  
Kenneth H. Pitetti
Keyword(s):  
Mental Retardation ◽  
Body Size ◽  
Children And Adolescents ◽  
Aerobic Capacity ◽  
Significant Influence ◽  
Moderate Mental Retardation ◽  
Leg Strength ◽  
And Gender ◽  
The Relationship ◽  
Shuttle Run

This study evaluated the relationship between leg strength and endurance run performance, independent of aerobic capacity (V̇O2peak), body size, and gender, in children and adolescents with mild or moderate mental retardation. Twenty-six individuals (15 boys and 11 girls) volunteered and underwent tests of V̇O2peak, isokinetic leg strength, and endurance run performance (600-yard ran/walk and 20-m shuttle run). Results showed that leg strength was significantly related to both types of run performance; however, when controlling for V̇O2peak, body size, and gender, leg strength was a more significant contributor to the 600-yard run/walk than to 20-m shuttle run performance. Gender did not influence these relationships. These data suggest that leg strength has a significant influence on endurance run performance in children and adolescents with mild or moderate mental retardation.

Dinosaur Macroevolution and Macroecology

2018 ◽  
Vol 49 (1) ◽  
pp. 379-408 ◽  
Author(s):  
Roger B.J. Benson
Keyword(s):  
Life History ◽  
Body Size ◽  
Reproductive Biology ◽  
Fossil Record ◽  
Structural Diversity ◽  
Body Plan ◽  
Adaptive Landscape ◽  
Species Diversification ◽  
Size Evolution ◽  
Body Size Evolution

Dinosaurs were large-bodied land animals of the Mesozoic that gave rise to birds. They played a fundamental role in structuring Jurassic–Cretaceous ecosystems and had physiology, growth, and reproductive biology unlike those of extant animals. These features have made them targets of theoretical macroecology. Dinosaurs achieved substantial structural diversity, and their fossil record documents the evolutionary assembly of the avian body plan. Phylogeny-based research has allowed new insights into dinosaur macroevolution, including the adaptive landscape of their body size evolution, patterns of species diversification, and the origins of birds and bird-like traits. Nevertheless, much remains unknown due to incompleteness of the fossil record at both local and global scales. This presents major challenges at the frontier of paleobiological research regarding tests of macroecological hypotheses and the effects of dinosaur biology, ecology, and life history on their macroevolution.

A guide to the nomenclature of heterochrony

1986 ◽  
Vol 60 (1) ◽  
pp. 4-13 ◽  
Author(s):  
Kenneth J. McNamara
Keyword(s):  
Twentieth Century ◽  
Causal Relationship ◽  
Fossil Record ◽  
Biogenetic Law ◽  
The Relationship

Since Haeckel's Biogenetic Law (‘ontogeny recapitulates phylogeny’) fell into disrepute early in the twentieth century, there has been intermittent debate, particularly in recent years (de Beer, 1958; Gould, 1977; Alberch et al., 1979; Alberch, 1980; Bonner, 1982; McNamara, 1982a), on the nature of the relationship between an individual's development and phylogenetic history. Important questions under discussion include the following: If a strong causal relationship does exist, what is its nature? How does it work? What is its importance in evolution? How can it be recognized in the fossil record?

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