A recent timeline of early animal fossils indicates a connection between sea level changes, marine oxygen variations, and the emergence of the first ancestors of modern animals. This research provides insights into the processes that drove the evolution of the earliest creatures, from which all major animal species originated. A team from the University of Edinburgh analyzed a collection of rocks and fossils from the Ediacaran-Cambrian interval, a 70-million-year period 580-510 million years ago. This era, marked by a significant increase in biodiversity according to fossil records, has puzzled scientists since Charles Darwin. The early marine animals of this period lived in an environment with significantly lower oxygen levels than today. Before this era, life was predominantly single-celled and simple multicellular organisms, but during the Ediacaran Period, organisms began to evolve more complex structures, enabling them to feed, reproduce, and move across the ocean floor. This period also saw the emergence of bilaterian animals, characterized by symmetrical body plans common in most modern species, including humans.
By integrating data from various sources, including radioactive dating and geochemical analysis of rock layers containing fossils, the team created a comprehensive timeline. This new chronology enabled a more detailed study of biodiversity trends for the period. The team linked these findings with additional chemical evidence from the geological record, confirming a relationship between significant sea level changes, periods of increased oxygen in shallow marine environments, and the emergence and diversification of early animal groups. This interplay led to several notable increases in biological diversity, known as the Avalon, White Sea, and Cambrian assemblages, each representing the arrival of new animal groups and the decline of others. The study, by reconstructing ancient environmental conditions, offers new insights into the ancient forces and pressures that shaped the earliest life on Earth. The team also noted gaps in the fossil record, suggesting that our current understanding of early animals might be biased by the concentration of fossil sites worldwide.
Dr. Fred Bowyer of the University of Edinburgh's School of Geosciences noted, "Constructing a timescale of early animal evolution using the rock record is a challenging task, made possible only through international and interdisciplinary research. An integrated global approach is essential. It helps identify biases in our records and reveals patterns in fossil appearances, sea level cycles, and environmental oxygen." Mariana Yilales Agelvis, a PhD student and co-author of the study, added: "Understanding what drives biodiversity is crucial in the quest to understand life. I am honored to build upon decades of interdisciplinary global research and contribute to a deeper understanding of the role sea level plays in early animal evolution."
