Discovery of "Fossil Graveyard" Shows What Life Looked Like 518 Million Years Ago

Friday, July 2, 2021

Chuandianella ovata, an extinct shrimp-like crustacean. Photo by Yunnan University

Have you often thought about traveling back in time and looking at how the Earth was millions of years ago? While time travel is not an available option at the moment, scientists have found the next best thing - a fossil deposit from over 500 million years ago with a diverse set of animals of that period.

The discovery was made near Kunming, in the southern province of Yunnan in China. The researchers from the Yunnan University and State Key Laboratory of Paleobiology in China and  Pennsylvania State University in the US have dated it back to the Cambrian period, approximately, 518 million years ago. The findings were recently published in Nature Ecology and Evolution.  

The deposit contains 2,846 specimens. It is not only the oldest found so far but is also the most diverse. It contains early vertebrates and other soft-bodied organisms who lived in the oceans. However, what has the researchers really excited is the presence of specimens in their larval and juvenile stages. "Juvenile fossils are something we hardly see, especially from soft-bodied invertebrates," Julien Kimmig, collections manager at the Earth and Mineral Sciences Museum and Art Gallery at Penn State University and one of the authors of the study said.  

The international team of researchers has identified 118 species so far in these deposits, 17 of which are new. These are ancestors of crustaceans, worms, trilobites, algae, sponges, modern-day insects, and early vertebrates. 

In the juvenile specimens, the researchers found the appendages to be intact and internal soft tissue can be seen. This is helping researchers learn about body parts in these animals, which have never been seen before. "The site preserved details like 3D eyes, features that have never really been seen before, especially in such early deposits," Sara Kimmig, assistant professor at Penn State University said.

The site of the fossil deposit is called the Haiyan Lagerstätte. A lagerstätte consists of several layers of sediment deposit where each layer is a burial event. Most of the deposits have been found in the lowest layer of this lagerstätte, which also showed the most diversity of species. The subsequent layers consist of other species, which the authors think is a representation of boom and bust periods in the ocean.

The authors hypothesize that the site might have offered protection from stronger ocean currents. Considering the high number of juvenile fossil specimens, an alternate hypothesis that is being considered is that these early organisms used the site as a paleonursery to protect their young ones from predators. A storm or sudden change in oxygen levels may have caused the sediment deposit leading to an extinction event. But if the site was indeed a paleonursery, then animal behavior hasn't changed much in over 500 million years. 

"The Haiyan Lagerstätte will be a wealth of knowledge moving forward for many researchers, not only in terms of paleontology but also in paleo-environmental reconstructions," said Sara Kimmig, who wants to analyze the sediments to understand the environmental conditions during the event.