Ecosystem in oil shale – Wissenschaft.de

The Messel Pit fossil site near Darmstadt offers unique insights into a warm period 48 million years ago. Today, paleontologists are not only searching for new species, but also trying to provide a comprehensive description of the extinct ecosystem – from biodiversity to nutrient cycles to climate.

By Karen Holricher

There is a world-class fossil site near Darmstadt: the Messel Crater. It is best known for the discovery of the prehistoric horse and early primate Darwinius massellae, called Ida. Small mammals, bats, terrestrial crocodiles, snakes and frogs as well as the remains of countless species of insects, arthropods, birds, fish and plants complete the very long list of finds. They were discovered in the shale that formed at the bottom of the lake. The lake was created as a result of a volcanic eruption about 48 million years ago, in the Eocene epoch. For nearly 100 years, people have been prospecting for coal and oil shale in Messel.

Today the place is strictly protected as a UNESCO World Heritage Site – no coal is mined, only fossils. Employees of the Senckenberg Natural Research Society and the Hessian State Museum have been excavating the slate rocks for decades. “Around 600 finds were made as a result of the nine-week excavation in 2023, which is an extraordinary amount,” says Torsten Wepler of the Hesse State Museum in Darmstadt. The lion’s share of the objects discovered, about 80 percent, are insect and plant remains. Fish are also plentiful, although there are a few species. After all, there are between ten and twenty vertebrates that are not considered fish every year. In 2023, another ancient horse was among the discoveries.

The latest scientific descriptions of the fossils cover freshwater shrimp, previously unknown species of spiders, birds, and snakes. “Very few freshwater shrimp fossils are known worldwide,” says Sonia Weidmann of the Messel Research Department of the Senckenberg Society. In the specimen you examined under a magnifying glass, you can see not only the exterior of the animal and its limbs, but also organs such as the ovaries and chewing stomach.

Christer Smith, a snake specialist at Senckenberg, talks about a baby snake found in shale in 2023. “This animal is so well preserved that you can even see the cartilage of its long trachea,” he says. Researchers had already discovered a snake fossil in Misil in 2020, and it had already been discovered by the native boa. In the Eocene, these families – who were not closely related – shared a European habitat. “This is amazing,” Smith marvels. Because today these snakes are not found together anywhere. So, the theory was that the two snake families competed too strongly with each other to coexist. But fossils contradict this. Giant snakes disappeared from Europe about 15 million years ago due to climate cooling in the Miocene. How they reached their current range is unknown.

Rebuilding the ecosystem

Purely systematic research on prehistoric animals is now increasingly taking a back seat in favor of describing the biodiversity of the time, and the relationships between organisms and ancient climate. The warm, tropical Misil River was teeming with fauna and flora. “Because of its extraordinary species richness, the Messe is a unique site in the world to study ecosystems in recent Earth history,” says geologist Philip Havlick, managing director of the World Heritage Site. A large group of Messel researchers is currently compiling all data on species abundance from all groups. Based on newer theoretical methods for calculating biodiversity, they want to estimate how many species live in Messel and how many they have not yet discovered. For the groups examined so far, there are statistically clear findings that as many as two-thirds of the species said to have lived in the area at that time were known, Smith says. Researchers do not expect any new types of fish to appear, but rather many types of insects and plants.

The group of herbivorous arthropods was the most species-rich, and remains so today. Two reasons for the emergence of the enormous diversity have been discussed: Either a large variety of host plants provided many different niches for invertebrate herbivores. Or each type of plant offers many different habitats. Thorsten Wappler and colleagues investigated this question and examined the effects of feeding on more than 10,500 fossil leaves from Messel and other sites. Depending on their diet and lifestyle, hungry herbivores left behind various tracks that could be used to determine who was munching on what. The data suggest that this phylum was able to become so diverse because the diverse array of plant species provided it with many different ecological niches. “So we can use fossils to test basic theories about the origin of biodiversity and draw conclusions about modern ecosystems,” Wapler says.

Messel Crater not only tells the history of animals and plants and their relationships to each other, but it also bears witness to the climate that prevailed there 48 million years ago. The terrain was roughly where southern Italy is today on the globe, i.e. in mid-latitudes. Global data indicate a tropical climate in the region. Researchers are currently analyzing what the microclimate and weather were like in the Messel ecosystem as part of the VeWA project (Past Warm Periods as Natural Analogues of Our ‘Elevated CO2’)₂‘-climate future) by examining rock samples for specific molecules. This way, you can document the alternation of dry and rainy seasons as well as temperature fluctuations with annual resolution. The result: The average temperature in Messel was 20 degrees Celsius, 12 degrees warmer than today.

But why do we want to know what the weather and climate changes were like in the Eocene period and how did they affect society? Havlick is convinced: “If we do not understand how things were in the past, we will have difficulty understanding what awaits us in the future in terms of climate change and associated changes in biodiversity.”

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