Rosa Rubicondior: Refuting Creationism - The Cambrian 'Explosion' Just Blew Up In Creationists' Faces

Cambrian explosion may have occurred much earlier than previously thought - Current events - University of Barcelona

Creationists have long misrepresented the so-called "Cambrian Explosion" as vindication of their belief in the spontaneous creation of complex multicellular life ex nihilo — as though organisms simply appeared, fully formed, without precursors. They portray it as an instantaneous event that defies evolutionary explanation, and falsely claim that it presents an insurmountable problem for evolutionary biology. In doing so, they even misquote the late Stephen Jay Gould, asserting that he admitted Darwinian evolution could not account for it and so invented the concept of "punctuated equilibrium" to paper over the cracks.

In a particularly striking display of cognitive dissonance, this version of events — supposedly occurring half a billion years ago — is frequently cited by the same creationists who insist the Earth is only 6,000 to 10,000 years old.

As is so often the case with creationist arguments, these claims are simply wrong. The Cambrian Explosion was not an instantaneous event, but a prolonged evolutionary process unfolding over some 10 million years, with evidence showing a transition from the static Ediacaran biota to the more mobile, complex organisms of the Cambrian. Gould, far from being an opponent of evolutionary theory, remained a staunch evolutionary biologist throughout his career. His now largely outdated concept of punctuated equilibrium was never an alternative to evolution, but rather an attempt to explain the appearance of abrupt change in the fossil record — a perception largely due to the compression of deep time in the geological column. When properly scaled, the fossil record easily accommodates the gradual evolution of complex traits.

Trace fossils are an indicator of the palaeoecological conditions in which the organism that generated them lived.

Now, new research by Olmo Miguez Salas of the University of Barcelona and Zekun Wang of the Natural History Museum in London has uncovered compelling evidence that pushes the roots of the Cambrian Explosion even further back in time. Their findings suggest that signs of mobility and bilateral body plans were already emerging within the Ediacaran biota. This extends the evolutionary runway leading into the Cambrian, giving more time for the radiation of novel body plans and for the development of evolutionary arms races—such as the emergence of predation, defence mechanisms, and sensory adaptations.

Their results are published in the journal Geology (paper here) and summarised in a news release from the University of Barcelona.

What information is there regarding the sub-phases of the Cambrian and changes to the biota that occurred within those phases? The Cambrian Period (~538.8 to 485.4 million years ago) is traditionally divided into several regional and global sub-stages or series, reflecting important biotic and sedimentological changes. These sub-phases mark significant milestones in the diversification and complexity of life, often tied to the fossil record of trilobites, small shelly fossils, and trace fossils.

Here's a breakdown of the Cambrian's subdivision and the major biotic changes associated with each phase:

Cambrian Subdivisions (Chronostratigraphy)

The Cambrian is divided into four official series by the International Commission on Stratigraphy (ICS):

Series: Terreneuvian

Approximate Age (Ma): 538.8 – 521
Traditional / Regional Equivalents: Includes Fortunian + Stage 2

Series: Series 2 (unnamed globally)

Approximate Age (Ma): 521 – 509
Traditional / Regional Equivalents: Often includes the Atdabanian–Botomian

Series: Miaolingian

Approximate Age (Ma): 509 – 497
Traditional / Regional Equivalents: Wuliuan, Drumian, Guzhangian

Series: Furongian

Approximate Age (Ma): 497 – 485.4
Traditional / Regional Equivalents: Paibian, Jiangshanian, Stage 10 (unnamed)

These divisions reflect radiations and turnovers of marine life, particularly arthropods, brachiopods, echinoderms, and early vertebrates.

Biotic Changes Across the Cambrian

Terreneuvian (538.8 – 521 Ma)

Key events: Start of the Cambrian Explosion. Dominated by small shelly fossils (SSFs), indicating mineralised skeletons evolving in multiple lineages.
Biota: Trace fossils (e.g. Treptichnus pedum) mark increasing complexity of burrowing organisms. Faunas mostly soft-bodied or lightly mineralised.
Notable groups: Early lobopodians, cnidarians, early mollusc-like forms.

Cambrian Series 2 (521 – 509 Ma)

Key events: Rapid diversification of trilobites, archaeocyathids (reef-building sponges), and more complex trace fossils.
Biota: Onset of major metazoan biomineralisation. First definitive bilaterian body plans well established.
Ecological shift: Expansion of tiered benthic ecosystems and mobile carnivores.

Miaolingian (509 – 497 Ma)

Key events: Cambrian Explosion peak; increased ecological structuring.
Biota: Dominance of trilobites, expansion of echinoderms, brachiopods, and soft-bodied taxa such as anomalocaridids (e.g. Anomalocaris).
Notable Lagerstätten: Burgess Shale-type deposits (e.g. Burgess Shale, Chengjiang) appear, preserving soft-bodied fauna in detail.
Predator-prey arms race: Emergence of complex eyes, hardened exoskeletons, and defensive behaviours.

Furongian (497 – 485.4 Ma)

Key events: Gradual faunal turnover leading into the Great Ordovician Biodiversification Event.
Biota: Decline in classic Cambrian groups like anomalocaridids; diversification of more derived trilobites, agnostoids.
Ecosystems: Begin to resemble more modern marine ecosystems; tiering and niche specialisation continue.

Biological Themes Across Cambrian Phases

Body plan innovation: Nearly all major metazoan phyla appeared during the Cambrian, many in their stem-group forms.
Niche expansion: Initial low-tier, sediment-dwelling organisms were joined by swimmers, predators, and suspension feeders.
Bioturbation and ecosystem engineering: Animals began reworking sediments, changing seafloor chemistry and sediment structure.
Predation pressure: Drove the evolution of hard parts, rapid movement, and sensory systems.

Additional Notes

Regional terminology (e.g., Atdabanian, Botomian, Toyonian) is still commonly used in Russian and Chinese stratigraphy, especially for Series 2 and earlier parts of the Miaolingian, and often aligns with specific fossil assemblages.
The Chengjiang Biota (c. 518 Ma) and Sirius Passet (c. 518–520 Ma) offer invaluable snapshots of soft-bodied early Cambrian life, especially in Series 2.
The Burgess Shale (~508 Ma) and similar deposits globally provide a rich record of mid-Cambrian ecosystems, including stem-group chordates and arthropods.

Cambrian explosion may have occurred much earlier than previously thought
The Cambrian explosion was an extraordinary phenomenon in the evolution of life on the planet that led to the emergence of many animal phyla and the diversification of species. During this period, some 530 million years ago, most of the basic body plans of organisms that have survived to the present day emerged. However, this great explosion of life that changed the evolutionary landscape on Earth may have occurred millions of years earlier than previously thought, a hypothesis now reinforced in a study published in the journal Geology.

This is a main conclusion of a new study that analyses the body profiles of organisms — symmetry, segmented bodies, exoskeletons, etc. — from around 545 million years ago by analysing trace fossils, which are the fossilized marks in rocks and sediments left by the activity of organisms in the past.

The authors of the article are the experts Olmo Miguez Salas, from the Faculty of Earth Sciences at the University of Barcelona, and Zekun Wang, from the Natural History Museum in London (United Kingdom).
Fossil traces of extinct animals

The Cambrian explosion is a unique period in the history of life that poses many unanswered questions. To delve into the biodiversity of this period, most studies in palaeontology tend to focus on the study of organisms that had hard parts. However, the study of trace fossils (or ichnofossils) opens up the possibility of discovering what the activity of hard-bodied, soft-bodied or skeletally deficient organisms preserved in the stratigraphic record was like.

The trace fossil record provides valuable information about evolutionary periods when soft-bodied fauna was dominant. Fossil traces reflect the behaviour of the organism that generates them, which is determined by habitat and responses to environmental stimuli. Therefore, they are an indicator of the palaeoecological conditions in which the organisms that generated them lived.

Dr Olmo Miguez Salas, co-author Beatriu de Pinós postdoctoral researcher
Departament de Dinàmica de la Terra I de l’Oceà
Universitat Barcelona, Catalunya, Spain.

The authors have focused on the study of trace fossils in the Ediacaran-Cambrian transition.

[the Ediacaran-Cambrian transition - ] a period of recognized palaeoevolutionary interest that was a turning point in the evolution of complex life on Earth. The Ediacaran fauna was dominated by complex, multicellular soft-bodied organisms. The transition to the Cambrian involved the extinction of much of the Ediacara fauna, and a rapid diversification of complex multicellular life forms with hard parts (e.g. exoskeletons). This is the evolutionary core from which most modern animal phyla emerged: what is known as the Cambrian explosion

Dr Olmo Miguez Salas.

In this transition, there was a radical change in biodiversity and in the structure of organisms and ecosystems.

The Cambrian explosion may have happened much earlier

The study published in Geology quantitatively indicates that organisms with slender body profiles thrived around 545 million years ago.

These organisms probably possessed coelomic hydrostatic bodies, with an anteroposterior axis, muscles and possibly segmentation. Furthermore, these organisms could move in a specific direction (directional locomotion) and probably possessed sensory capabilities to move and feed on heterogeneous substrates in a habitat dominated by microbial mats. Therefore, the so-called Cambrian explosion and its evolutionary implications may have occurred much earlier than estimated.

Dr Olmo Miguez Salas.

These adaptations in body profile and mobility allowed these early animals to thrive in increasingly dynamic and complex environments, an ecological engineering that could promote evolutionary innovations. The methodology of the study was based on the analysis of the linear proportionality exhibited by the trace trajectories of modern and fossilized animals. Subsequently, this scaling law has been applied to locomotor traces of Ediacaran-Cambrian fossils (e.g. Archaeonassa, Gordia, Helminthopsis and Parapsammichnites).

Although some previous studies had described trace fossils associated with mobile benthic bilateral organisms in the Ediacara fauna, detailed quantitative approaches were lacking and there were still many unknowns about the body shape of these organisms (length, width, cephalization, etc.). The findings of the new study establish an innovative quantitative approach to analysing the fossil locomotion traces from ancient times, early animal anatomy and palaeoecological dynamics.

This new discovery opens the door to quantitatively study future Ediacara trace fossils discovered in the coming years and to corroborate that the Cambrian explosion did not happen in the Cambrian, but many millions of years earlier. Moreover, the scaling laws obtained in this study enable the study of the morphological evolution of different faunal phyla generating fossil locomotion traces, not only during this evolutionary period, but also during other evolutionary periods of similar importance, such as the great diversification event of the Ordovician.

Dr Olmo Miguez Salas.

Reference article:
Wang, Zekun; Miguez-Salas, Olmo.
Quantitative decoding of Ediacaran locomotory trace fossilmorphologies: Evidence for the emergence of slender anterior-posterior body profiles
Geology, June 2025. DOI: 10.1130/G53332.1.

Abstract
Trace fossils are vital for studying early animals and their co-evolution with paleoenvironments during the terminal Ediacaran, a period with sparse body fossil records. Thus, patterns of morphologic evolution are difficult to untangle for Ediacaran trace-makers and quantitatively unexplored. In this study, we use the integral scale, which reflects the distance within which a trajectory (i.e., force and displacement) is self-correlated, as a potential indicator for the characteristic length of trace-maker’s locomotion. By analyzing modern and fossilized animal-trace-correlated trajectories, a proportionality between the characteristic locomotory length and the trajectory integral scale is found. Since the length of the structure producing locomotion is no larger than that of the body, the characteristic locomotory length also reflects the minimal body length. Applying this scaling law to Ediacaran−Cambrian locomotory trace fossils (e.g., Archaeonassa, Gordia, Helminthopsis, Parapsammichnites), we identify clear evidence of slender anterior-posterior body axes after around 545 Ma, with gradually increasing minimal body length-to-width ratios to up to 4−12. The trace-makers probably had relatively rigid bodies with robust hydrostatic nerve-muscle systems enhancing directional sensation and movement, enabling them to thrive in dynamically complex, heterogeneous, and shifting habitats. These adaptations likely drove niche partitioning and cascading diversification, underpinning the evolutionary roots of the Cambrian Explosion and more familiar animals of the Phanerozoic. Our findings establish a novel quantitative approach to studying deep-time locomotory trace fossils, offering robust insights into early animal anatomy and paleoecological dynamics.

INTRODUCTION
Trace fossils are the results of ancient organism-substrate interactions constituting complementary materials to body fossils in paleontological research. They provide unique insights into the anatomy, behavior, and evolution of the trace-makers, particularly during evolutionary radiations/extinctions. These fossils are informative in studying early complex animals from the Proterozoic–Cambrian transition, especially given the limited body fossil record (Mángano and Buatois, 2016). However, except for the traces left by typical macro-scale Ediacaran biota that went extinct shortly before the Cambrian, such as Kimberella (Kimberichnus), Yorgia/Dickinsonia (Epibaion), and Yilingia, many trace fossils from this period typically had linear (i.e., nonbranching, non-retreated) paths. These traces include Helminthoidichnites, Helminthopsis, Gordia, Parapsammichnites, and Planolites (Mángano and Buatois, 2016), which persisted into the Phanerozoic.

Previous studies have suggested a bilaterial metazoan origin for these trace fossils based on features such as furrows, three-dimensional burrows, linings, sequential probes, and complex movements like slightly sinusoidal or spiral trajectories (Tarhan et al., 2020; Jensen, 2003; Mángano and Buatois, 2016; Gehling and Droser, 2018). These features also indicated the existence of a coelomate hydrostatic body (Mángano and Buatois, 2020.1) or a certain degree of sensorial capacities (Gehling and Droser, 2018). However, trace fossil records alone provide limited insight into the evaluation of anterior-posterior differentiation (Evans et al., 2020.2), leaving it difficult to determine progenitor morphology, from minimal body length to type of locomotors (structures responsible for smallest independent locomotory patterns) to potential cephalization. Therefore, identifying a slender anterior-posterior (A–P) axis holds significant evolutionary importance.

By analyzing trace-makers’ morphometrics, specifically body sizes and locomotors, we can correlate trace fossils with anatomical features (Mancinelli and Pasquali, 2016.1). Because the body part producing locomotion never exceeds the total body size, the length of the characteristic locomotory structure (an independent locomotor or a group of locomotors coordinating for the same direction) also reflects the minimal body length and whether the organism has a slender A–P axis. In this study, we use the integral scale of the signal of the magnitude of the trajectory curvature to estimate the size of the trace-maker’s locomotory structure. By calibrating this scaling relationship with fossil records and modern animals, we evaluate locomotory trace fossils from the Proterozoic–Cambrian transition to identify traces potentially made by organisms with a slender A–P axis and infer possible locomotory modes.

Wang, Zekun; Miguez-Salas, Olmo.
Quantitative decoding of Ediacaran locomotory trace fossilmorphologies: Evidence for the emergence of slender anterior-posterior body profiles
Geology, June 2025. DOI: 10.1130/G53332.1.

Copyright: © 2025 The authors.
Published by GeoScienceWorld. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)

This latest research adds yet another layer of difficulty for creationists seeking to dismiss the Cambrian Explosion as evidence of supernatural creation. By pushing the origins of mobility and bilateral symmetry further back into the Ediacaran, it reinforces the view that the Cambrian radiation was not a spontaneous, inexplicable leap, but a protracted evolutionary process grounded in well-understood mechanisms: environmental pressures, ecological interactions, genetic innovation, and deep time.

The existence of transitional forms—organisms showing partial or emerging versions of traits that later become widespread—directly contradicts the creationist demand for discrete, unchanging "kinds" that appear fully formed. Bilaterally symmetrical, mobile organisms with clear evolutionary links to later Cambrian fauna do not fit the creationist model of instant, saltational creation. Instead, they support what evolutionary biologists have long argued: that major body plans arose gradually, through a series of small, accumulative changes shaped by natural selection.

Moreover, the idea that such developments occurred over tens of millions of years exposes the inconsistency in young-Earth creationist timelines. If Earth is only 6,000 to 10,000 years old, then there should be no Ediacaran biota, no stratified sedimentary rock layers, and no sequence of fossils showing a transition from simple to complex. The fossil record clearly shows otherwise. The careful stratigraphic placement of these new trace fossils, and their alignment with broader geological and biological patterns, is entirely consistent with evolutionary theory—and entirely at odds with biblical literalism.

Far from being a problem for evolutionary biology, the extended timeline of the Cambrian diversification strengthens it. It makes clear that what creationists present as a fatal flaw is, in fact, a textbook case of how science works: explaining apparent anomalies through evidence, revision, and refinement. As usual, it’s not the science that’s lacking coherence—it’s the creationist narrative.

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