Ediacaran Biota
About the Ediacaran
The Ediacaran is the topmost stratigraphic interval of the Neoproterozoic Erathem, just below the Cambrian System. The most distinctive aspect of Ediacaran rocks is that they record the abrupt appearance of a diverse suite of macroscopic fossils.
Ediacaran assemblages consist of predominantly benthonic and soft-bodied organisms, many of which do not present a clear affinity with animal groups preserved in overlying Cambrian strata (Darroch et al., 2018; Droser & Gehling, 2015). Some researchers have suggested that most Ediacaran organisms are so distinct in their body plans’ supposed functionality that they would require classification in new higher-order clades, but other researchers characterize some members of the Ediacaran biota as ancestral to clades of Cambrian organisms (Xiao and Laflamme, 2009; Droser et al., 2017; Dunn & Liu, 2019).
The abrupt appearance of multicellular Ediacaran organisms has remained an enigmatic feature of the geologic record, although significant changes in geochemistry or nutrients availability have been suggested as its possible cause (Bobrovskiy et al., 2020; Droser et al., 2017). However, any connection to long sought after macroevolutionary mechanisms for such radiation is, at best, unclear (Briggs and Crowther, 2001).
The disappearance of the Ediacaran biota is also an enigmatic discontinuity in the fossil record, attributed to external abiotic factors or biotic innovations, such as the advent of predation (Narbonne, 2005; Darroch et al., 2018). Some researchers dispute the notion of an actual sharp extinction boundary and suggest a more gradual transition or faunal replacement (Mussini & Dunn, 2024).
The apparent lack of gradual fossil series connecting ancestral Ediacaran and Cambrian taxa is just as significant as the abrupt appearance of complex multicellular organisms documented in the Ediacaran rocks.
In summary, the Ediacaran biota is a highly significant example of distinctive patterns found in the fossil record, such as abrupt coordinated appearances and disappearances of fossil taxa, high disparity from the lowest level of occurrence of fossil taxa, and lack of clear gradual/sequential series of intermediates. Additionally, the ecology represented by these organisms is quite distinctive in its organization from the multi-tiered trophic chain of Phanerozoic fossil assemblages.
Stratigraphic range of representative Ediacaran fossils. Taxa marked by a star indicate fossils present in the GRI collection. Icons of organisms, illustrated in part with the help of AI, are for general illustration purposes and do not intend to convey anatomical details. Chart is based on data from Narbonne (2005), Xiao & Laflamme (2009), Laflamme et al. (2013), Grazhdankin (2014), Darroch et al. (2018), Bobrovskiy et al. (2020), Ebbestad et al. (2022), and Mussini & Dunn (2024).
References:
Briggs, D.E.G. and Crowther, P.R., 2001. Palaeobiology II. Osney Mead, Oxford: Blackwell Science. pp. 25-26.
Narbonne, G.M., 2005. The Ediacara biota: Neoproterozoic origin of animals and their ecosystems, Annual Review of Earth and Planetary Sciences, 33(1), pp. 421–442. DOI: 10.1146/annurev.earth.33.092203.122519.
Xiao, S. and Laflamme, M., 2009. On the eve of animal radiation: Phylogeny, ecology and evolution of the Ediacara biota, Trends in Ecology & Evolution, 24(1), pp. 31–40. DOI: 10.1016/j.tree.2008.07.015.
Laflamme, M., Darroch, S.A., Tweedt, S.M., Peterson, K.J. and Erwin, D.H., 2013. The end of the Ediacara biota: Extinction, biotic replacement, or Cheshire Cat?. Gondwana Research, 23(2), pp.558-573. DOI: 10.1016/j.gr.2012.11.004.
Grazhdankin, D., 2014. Patterns of evolution of the Ediacaran soft-bodied biota. Journal of Paleontology, 88(2), pp.269-283. DOI: 10.1666/13-072.
Darroch, S.A., Smith, E.F., Laflamme, M. and Erwin, D.H., 2018. Ediacaran extinction and Cambrian explosion. Trends in Ecology & Evolution, 33(9), pp.653-663. DOI: 10.1016/j.tree.2018.06.003.
Bobrovskiy, I., Hope, J.M., Golubkova, E. and Brocks, J.J., 2020. Food sources for the Ediacara biota communities. Nature Communications, 11(1), p.1261. DOI: 10.1038/s41467-020-15063-9.
Ebbestad, J.O.R. et al., 2022. Distribution and correlation of Sabellidites cambriensis (Annelida?) in the basal Cambrian on Baltica’, Geological Magazine, 159(7), pp. 1262–1283. DOI: 10.1017/S0016756821001187.
Mussini, G. and Dunn, F.S., 2024. Decline and fall of the Ediacarans: late‐Neoproterozoic extinctions and the rise of the modern biosphere. Biological Reviews, 99(1), pp.110-130. DOI: 10.1111/brv.13014.
Ediacaran Fossils at GRI
This enigmatic Ediacaran fossil keeps scientists guessing about its affinity (animal or not?), its mode of life
(mobile or not?), and even its symmetry (bilateral or not?).
There is some dispute as to whether these fossils are the remains of clustered individual cnidarian-like animals, or an aggregation of bacterial colonies.
Aspidella could be a holdfast for an attached organism, or a variety of creatures of similar morphology.
One of the few taxa found across the Ediacaran-Cambrian boundary, it is representative of tube-forming worms characteristic of the uppermost Ediacaran.
Scientists have a better idea of how this creature may have looked, thanks to well-preserved specimens found in Namibia.
This disk-shaped fossil is representative of a unique group of organisms exhibiting threefold symmetry.
Probably a slug-like creature, its fossils have been found associated with scrapings interpreted as feeding traces.
Further Reading
Over the years, Dr. Günter Bechly has written a series of penetrating articles for Evolutions News, critically appraising interpretations about the affinity of Ediacaran taxa. Most of them are listed here, in chronological order:
Fossil Friday: Cloudina Still Lacks the Guts to Be a Worm (2023)
Fossil Friday: Dickinsonia, the Ediacaran Animal that Wasn’t (2022)
Evans et al. (2021): All Four Examples Debunked (2021)
Unknown Biology of Trilobozoa (2021)
Uncertain Affinities of Trilobozoa (2021)
Examining Potential Other Trilobozoans (2021)
The Enigmatic Tribrachidium and Trilobozoa (2021)
Ediacarans Are Not Animals (2021)
A Precambrian House of Cards (2021)
Namacalathus Revisited — Not Much to See (2021)
Resurrecting Namacalathus as an Ediacaran Animal (2021)
Was Kimberella a Precambrian Mollusk? (2020)
Kimberella — A Checkered History (2020)
Conflicting Views about Kimberella’s Ecology (2020)
Kimberella — Conflicting Evidence from Taphonomy (2020)
Kimberella — Interpreting the Fossils (2020)
Kimberella — Four Phases of Interpretation (2020)
Reconstructing Kimberella — The Disputed Anatomy in Detail (2020)
Kimberella — Controversial Scratch Marks (2020)
Kimberella — Traces and a Trace-maker (2020)
Kimberella — Locomotory Tracks (2020)
Kimberella — The Oldest Radula (Not) (2020)
Kimberella and Controversial Relationships — A Chronological Synopsis (2020)
Kimberella and Controversial Relationships — A Chronological Synopsis, Continued (2020)
Kimberella Is No Solution to the Cambrian Conundrum (2020)
Namacalathus, Alleged Ediacaran “Animal,” Fails to Refute Abrupt Cambrian Explosion (2020)
Namacalathus, an Ediacaran Lophophorate Animal? (2020)
The Myth of Precambrian Sponges (2020)
Ancestor of All Animals in 555-Million-Year-Old Ediacaran Sediments? (2020)
Did Cloudinids Have the Guts to Be Worms? (2020)
“Ice Cube” Study of Ediacaran Fossils Is Junk Science (2019)
Why Dickinsonia Was Most Probably Not an Ediacaran Animal (2018)