Scientists have shown conclusively for the first time that tiny marine organisms in polar oceans survived the mass extinction event that wiped out prehistoric dinosaurs because they needed less energy and were more tolerant to darkness.
The study, led by the University of Bristol and published in the journal Nature, sought to solve a longstanding evolutionary enigma: what factors determined whether marine species would survive a mass extinction event known as the Cretaceous-Paleogene (K-Pg) boundary some 66 million years ago? Findings revealed that being small and accustomed to darkness proved to be the vital attributes.
Study lead author Dr Rui Ying said:
“It’s an exciting breakthrough. For so many years scientists have been unable to test what actually decided whether a species prevailed or perished because the extinction event involves multiple environmental changes like ocean acidification and darkness.”
“It is difficult to understand the causality because of the lack of fossil data and environmental proxy data, especially at century timescale. Using a numerical model, I looked at the base of the food chain – plankton – which helped us to identify the most likely cause and the best survival strategies for plankton.”
The Cretaceous–Paleogene (K–Pg) boundary is an ancient and much-studied geological signature marking the mass extinction that wiped out non-avian dinosaurs, separating the Mesozoic Era (the age of reptiles) from the Cenozoic Era (the age of mammals). It is thought that the impact of an asteroid, called Chicxulub, caused the extinction of around 75% of species in the fossil record by triggering catastrophic environmental changes.
Despite decades of research, the mechanisms linking the environmental changes to the selective extinction patterns observed in the fossil record have until now been unresolved. But by creating and deploying a unique model which maps ecosystem traits globally, the scientists have been able to establish what attributes resulted in the marine plankton community’s survival.
Dr Ying, who is now a Senior Research Associate at the University of East Anglia, said:
“The model is based on trades and the trade-off of how often they are eaten by predators and what they can eat against specific attributes, such as temperature, light level and body size.”
Study co-author Dr Fanny Monteiro, Associate Professor in Ocean Sciences at the University of Bristol, explained:
“The body size and abundance of small plankton mean the organisms rely on less energy, increasing their likelihood of survival. An ability to deal with lower light and darkness and turbulent waters in higher latitudes also makes them more adaptable to polar regions. In contrast, species adapted to higher light and warmer waters were more vulnerable to this type of mass extinction.”
The model allowed the traits of millions of organisms to be analysed and quantified with unprecedented accuracy, providing important insights into the physical and chemical changes linked to diversity. Besides shining a light on the distant past of marine life, the research can also help inform forecasts of how ecosystems might respond in future.
Study co-author Professor Daniela Schmidt, Professor of Earth Sciences at the University of Bristol, said:
“This study not only demonstrates how trait-based models can help us better understand biodiversity crises in ancient history, but it also has potential to indicate how less light and hotter environments, as a result of global warming, might impact current and future ecosystems.”
The research was funded by China Scholarship Council (CSC)-Bristol PhD Scholarship and NERC grants.