Cambrian Explosion Occurred Millions of Years Earlier than Previously Thought: Study

Paleontologists have analyzed the body profiles of Ediacaran-Cambrian organisms by using trace fossils as proxies for body fossils.

A reconstruction of early Cambrian ocean life in South China. Image credit: Dongjing Fu.

The so-called Cambrian explosion is commonly labeled as the time in Earth’s history when animal body plans suddenly appear.

Most studies suggest that this event occurred between 541 million and 530 million years ago at the beginning of the Cambrian period.

“The Cambrian explosion is a unique period in the history of life that poses many unanswered questions,” said Dr. Olmo Miguez Salas from the Universitat Barcelona and Dr. Zekun Wang of the Natural History Museum, London.

“To delve into the biodiversity of this period, most studies in paleontology tend to focus on the study of organisms that had hard parts.”

“However, the study of trace fossils 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 were dominant.”

“Fossil traces reflect the behavior of the organism that generates them, which is determined by habitat and responses to environmental stimuli.”

“Therefore, they are an indicator of the paleoecological conditions in which the organisms that generated them lived.”

In their study, the authors focused on trace fossils in the Ediacaran-Cambrian transition, a period of recognized paleoevolutionary interest that was a turning point in the evolution of complex life on Earth.

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

“The Ediacaran fauna was dominated by complex, multicellular soft-bodied organisms,” Dr. Miguez Salas said.

“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.”

The findings show that organisms with slender body profiles thrived around 545 million years ago (Ediacaran period).

“These organisms probably possessed coelomic hydrostatic bodies, with an anteroposterior axis, muscles and possibly segmentation,” Dr. Miguez Salas said.

“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”.

“These adaptations in body profile and mobility allowed the early animals to thrive in increasingly dynamic and complex environments, an ecological engineering that could promote evolutionary innovations.”

The team’s paper appears in the journal Geology.

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Zekun Wang & Olmo Miguez-Salas. Quantitative decoding of Ediacaran locomotory trace fossil morphologies: Evidence for the emergence of slender anterior-posterior body profiles. Geology, published online June 9, 2025; doi: 10.1130/G53332.1