A newly developed timeline of early animal fossils has unveiled a compelling link between fluctuations in sea levels, changes in marine oxygen, and the emergence of the earliest ancestors of modern-day animals. This study provides critical insights into the driving forces behind the evolution of the earliest organisms, from which all major animal groups originated.
Researchers from the University of Edinburgh meticulously analyzed a collection of rocks and fossils from the Ediacaran-Cambrian interval – a pivotal period 580–510 million years ago that witnessed a remarkable surge in biodiversity, a phenomenon that has perplexed scientists since the time of Charles Darwin.
During this era, the early animals thrived in the sea, adapting to an environment with lower oxygen levels in both the air and ocean than what we experience today.
The Ediacaran Period witnessed a significant transformation as creatures evolved from single-celled and simple multi-celled organisms to more complex forms with structured body plans that enabled feeding, reproduction, and movement across the ocean floor.
This period also saw the rise of bilaterian animals, which share symmetrical body plans with many modern species, including humans.
By integrating data from multiple sources, including radioactive dating and geochemical analysis of rock layers containing fossils, the team created a comprehensive timeline of major fossil discoveries and environmental data. This new chronology provides unprecedented insight into biodiversity trends during the studied period.
Moreover, combining these findings with additional chemical evidence from the geological record confirms a correlation between significant shifts in global sea levels, periods of increased oxygen in shallow marine environments, and the emergence and proliferation of early animal species.
The interplay of environmental dynamics led to significant bursts in biological diversity, giving rise to the Avalon, White Sea, and Cambrian assemblages. Each marked the emergence of new animal groups and the decline of others.
By reconstructing ancient environmental conditions, this study provides crucial insights into the forces that shaped early life on Earth. Additionally, the research revealed gaps in the fossil record, indicating biases in our current understanding of early animals due to the limited locations where fossils have been unearthed and studied.
“Constructing a timescale of early animal evolution using the rock record is a daunting task, only made possible through international and interdisciplinary research,” said Dr Fred Bowyer of the University of Edinburgh’s School of Geosciences. “But an integrated global approach is crucial. It exposes biases in our records while also revealing patterns in fossil appearances, sea level cycles, and environmental oxygen.”
Mariana Yilales Agelvis, a PhD student in the School of Geosciences who co-authored the study, said: “Knowing what drives biodiversity is a fundamental piece of knowledge in the puzzle of life. I feel very privileged to have built upon decades of interdisciplinary global research and contributed to a better understanding of the role that sea level plays in early animal evolution.”
Journal reference:
- Fred T. Bowyer, Rachel A. Wood, Mariana Yilales. Sea level controls on Ediacaran-Cambrian animal radiations. Science Advances, 2024; DOI: 10.1126/sciadv.ado6462