Fossil Friday: New Research on How Delicate Soft-Bodied Organisms Can Be Perfectly Preserved
This Fossil Friday features the Cambrian arthropod Waptia fieldensis from the famous Burgess Shale. However, today we will not look into a particular fossil or group of organisms, but into the exceptional mode of fossil preservation of some of the oldest known animals from the Cambrian and the recently changed interpretation of how these fossil layers were formed. Paleontologists have generally assumed and postulated that perfect and complete preservation, especially of delicate soft-bodied organisms, suggests a gentle deposition in situ without significant transport that would certainly damage these fragile bodies. This view has been challenged by experimental studies that showed such organisms can remain entirely intact even when transported more than 20 km in turbulent sediment flows (Bath Enright et al. 2017). But how does this apply to real world fossil localities, especially the crucial sources for exquisitely preserved fossils of the first animals from the Cambrian Explosion? Two new studies have revised my views on two key localities, i.e., the Burgess Shale and the Emu Bay Shale.
Burgess Shale
The Burgess Shale, a world-renowned fossil site in the Canadian Rockies, provides one of the most complete windows into the Cambrian Explosion, a period about 508 million years ago when a remarkable diversity of complex life forms first appeared in the fossil record. Discovered in 1909 by paleontologist Charles Doolittle Walcott, the Burgess Shale is exceptional not only for its abundance of fossils but also for the extraordinary preservation of soft-bodied organisms, which are typically absent from the fossil record. This preservation includes fine details of tissues and appendages, capturing intricate anatomical features that illuminate the early history of animals. Scientific explanations for this unique preservation focus on taphonomy, the processes that affected these organisms from death to their fossilization, emphasizing the role of rapid burial and anoxic conditions.
According to the prevailing taphonomic model, the organisms in the Burgess Shale were buried quickly by underwater mudslides or turbidites, which were common in the deep marine environments where these creatures lived. These mudslides would have buried the organisms in a fine-grained, clay-rich matrix, isolating them from scavengers and decay. Furthermore, the water column above the burial site was likely low in oxygen, creating anoxic or dysoxic conditions that inhibited bacterial decomposition. This lack of oxygen, combined with rapid burial, allowed the soft tissues of these animals to be preserved in exquisite detail. Over time, mineral replacement of organic materials took place, particularly through carbon films that retained fine anatomical features. In some cases, other mineral replacements occurred, stabilizing the structures long enough for them to fossilize.
Further research emphasized the precise geochemical and sedimentological conditions that allowed for this unique preservation. Studies on clay mineralogy and trace metal concentrations in the Burgess Shale suggested that specific chemical interactions in the sediment helped to inhibit decay, possibly by creating an environment toxic to decay microbes. As a result, the Burgess Shale represents not only a key snapshot of Cambrian life but also an extraordinary example of the role that taphonomic processes play in determining what we see in the fossil record.
Thus, even the traditional view considered the Burgess Shale fossil assemblage as caused by catastrophic rapid burial. However, according to Bath Enright et al. (2017), “the exceptional preservation of organisms within the deposits has been used to argue that transport of these animals must have been minimal,” which those authors doubted based on their experiments. In a more recent follow-up study (Bath Enright et al. 2021), the same authors tested this with flume experiments to create analog flows and showed that transport of polychaete worms over tens of kilometers does not induce significant damage. They concluded “that the organisms of the Burgess Shale in the classic Walcott Quarry locality could have undergone substantial transport and may represent a conflation of more than one community.” Co-author Dr. Nic Minter commented in the press release by the University of Portsmouth (2021) that “this finding might surprise scientists or lead to them striking a more cautionary tone in how they interpret early marine ecosystems from half a billion years ago.” It goes without saying that this result of course also has important implications for our understanding of the over 40 known localities of the Burgess-Shale-Type (BST) preservation.
Emu Bay Shale
Such another BST locality is the Emu Bay Shale, located on Kangaroo Island in South Australia. It represents one of the most significant Cambrian fossil sites outside North America, providing valuable insights into the Cambrian Explosion, especially regarding arthropod diversity. Like the Burgess Shale, the Emu Bay Shale is remarkable for its exceptional preservation of soft tissues in fossils, including eyes, digestive tracts, and delicate appendages, which offer a detailed view of early animal anatomy. Dating to around 514 million years ago, it preserves a diverse array of Cambrian life forms, particularly trilobites and anomalocaridids, which are preserved with high fidelity, showing fine structures not typically fossilized.
Scientific views on the taphonomy of the Emu Bay Shale attributed its preservation quality to rapid burial and the local environmental conditions. Similar to the Burgess Shale, researchers suggested that the fossils were entombed quickly in fine-grained sediment, likely during submarine mudflows that swept organisms into deeper, oxygen-poor waters. Anoxic conditions in the burial environment would have slowed bacterial decay and minimized disruption by scavengers, while fine sediment encasement shielded delicate structures from mechanical breakdown. This unique combination of rapid burial and anoxia, possibly supplemented by specific chemical interactions in the sediment, allowed the Emu Bay Shale to capture fine anatomical details, adding a vital piece to our understanding of Cambrian ecosystems.
According to a brand new study by Gaines et al. (2024), published in the journal Science Advances, the Emu Bay Shale has to be newly interpreted. The authors document evidence for downslope mass transport of soft-bodied organisms in “density-driven sediment gravity flows” caused by “episodic high-energy events.” The press release explains that the sediments were “were catastrophically deposited into the ocean by debris flows,” which is “not where you would expect to see delicate, soft-bodied creatures preserved” (Gaines quoted in NSF 2024). The authors concluded that most taxa of the more than 25,000 fossils were transported and thus not buried in situ, which explains why “before these findings, the research community debated whether the Emu Bay Shale represented a shallow or deep environment” (NSF 2024).
Perfect Fossil Preservation Does Not Exclude Long Transport
What makes the revised understanding of the taphonomy of these two key Cambrian localities very interesting is that the perfect preservation of the fossil from these localities is now considered to be consistent with a long transport in rough and turbulent sediment flows. Of course, this does not just apply to the Burgess Shale and Emu Bay Shale localities but can be extrapolated to numerous other “Konservat-Lagerstätten” with well-preserved marine and terrestrial fossils around the globe, such as the Devonian Hunsrück Shale in Germany and the Cretaceous Jehol biota in China (Bath Enright et al. 2017). A good example is the new study by O’Connell et al. (2024) about the terminal Ediacaran Nama biota, which showed that soft-bodied and biomineralizing organisms were transported in sediment gravity flows induced by storms and others events. The authors found that “nearly all soft-bodied and biomineralizing organisms preserved in the studied units were transported prior to final burial.” The authors also mention that “other work suggests that turbulent and transitional flows can transport soft-bodied organisms great distances with little damage (ca 20 km; Bath Enright et al., 2017, 2021).”
Evolution is Neither a Fact nor Knowledge
These new interpretations show how quickly yesterday’s scientific textbook wisdom may be refuted as obsolete misinterpretation. In the strict sense of the notion of “knowledge” we do not know anything with certainty about the distant past. All we have is an ever-changing set of very preliminary and often weakly supported conjectures, combined with wild speculations and fancy storytelling, that more often than not later turn out to have been plausible but false. The famous philosopher of science Karl Popper cherished this procedure of “conjectures and refutations” as the very core of the scientific method. However, there is a fundamental difference between repeatable and observable law-like processes that can be mathematically modelled and empirically tested, and singular events in the past that can only be probabilistically inferred based on circumstantial evidence and certain assumptions. Earth history, paleobiology, and evolutionary biology are all historical “soft” sciences that cannot be considered as on an equal footing with experimental “hard” sciences like physics, chemistry, genetics, or physiology. Only the latter sciences provide us with all the benefits of modern medicine and technology. The historical sciences are basically ivory tower musings of hardly any practical value and dubious scientific status. Therefore, I consider the famous dictum of evolutionary biologist Theodosius Dobzhansky — that “nothing in biology makes sense except in the light of evolution” — as one of the biggest myths and blunders in modern science. On the contrary, all the just-so-stories of macroevolution are completely dispensable in all of real (experimental) biology. I would even suggest that “not much in biology makes sense except in the light of design,” which is why design language is so ubiquitous and indispensable even in the mainstream biosciences.
References
Bath Enright OG, Minter NJ & Sumner EJ 2017. Palaeoecological implications of the preservation potential of soft-bodied organisms in sediment-density flows: testing turbulent waters. Royal Society Open Science 4(6), 170–212. DOI: https://doi.org/10.1098/rsos.170212
Bath Enright OG, Minter NJ, Sumner EJ, Mángano MG & Buatois LA 2021. Flume experiments reveal flows in the Burgess Shale can sample and transport organisms across substantial distances. Communications Earth & Environment 2: 104, 1–6. DOI: https://doi.org/10.1038/s43247-021-00176-w
Gaines RR, García-Bellido DC, Jago JB, Myrow PM & Paterson JR 2024. The Emu Bay Shale: A unique early Cambrian Lagerstätte from a tectonically active basin, Science Advances 10(30): eadp2650, 1–9. DOI: https://doi.org/10.1126/sciadv.adp2650
NSF (National Science Foundation) 2024. A remarkable fossil assemblage gets a new interpretation. Phys.org October 30, 2024. https://phys.org/news/2024-10-remarkable-fossil-assemblage.html
O’Connell B, McMahon WJ, Nduutepo A, Pokolo P, Mocke H, McMahon S, Boddy CE & Liu AG 2024. Transport of ‘Nama’-type biota in sediment gravity and combined flows: Implications for terminal Ediacaran palaeoecology. Sedimentology early view, 1–43. DOI: https://doi.org/10.1111/sed.13239
University of Portsmouth 2021. Fossil secret may shed light on the diversity of Earth’s first animals. Phys.org June 2, 2021. https://phys.org/news/2021-06-fossil-secret-diversity-earth-animals.html
