104 million-year-old fossils unveil ocean past

Scientists have found fossil evidence that higher invertebrates, specifically irregular hedgehogs or sea urchins, have steadily colonized the deep sea for at least 104 million years since the Cretaceous period. By analyzing more than 40,000 spines from sediment samples, the team detected evolutionary changes over time, particularly after major mass extinction events, and suggested possible impacts of future global warming on deep-sea ecosystems.

A team led by the University of Göttingen described the early occurrence of irregular sea urchins in the ocean depths.

Deep in the ocean abyss, the oldest and most primitive forms of life on our planet are believed to have formed long ago. Nowadays, the deep sea is famous for its exotic fauna. Researchers delve into how Classify Diversity on the ocean floor has evolved over time.

There are hypotheses that deep-sea ecosystems have been repeatedly reborn after numerous mass extinctions and marine disturbances. Hence, marine life present at these depths may be relatively recent in Earth’s timeline. However, mounting evidence indicates that parts of this underwater world may be older than previously assumed.

A research team led by the University of Göttingen has presented the first fossil evidence of stable colonization of the deep sea floor by strata. invertebrates For a period of at least 104 million years. Fossil spines of irregularly shaped sea urchins (sea urchins) indicate their presence as long ago as Paleolithic Cretaceous period period, as well as its development under the influence of fluctuating environmental conditions. The results were published in the journal Plus one.

A collection of sea urchin spines from different periods of Earth's history showing the diversity of shapes

A collection of sea urchin spines from different periods of Earth’s history showing the diversity of shapes. Credit: PLOS ONE, 2023 Weisz et al.

The researchers examined more than 1,400 sediment samples from wells in the Pacific, Atlantic and Southern Oceans representing past water depths from 200 to 4,700 metres. They found more than 40,000 pieces of thistle, and attributed them to a group called irregular hedgehogs, based on their structure and shape.

For comparison, the scientists recorded the morphological characteristics of the spines, such as shape and length, and determined the thickness of about 170 spines from each of the two time periods. As an indicator of the total mass of sea urchins in the habitat — their biomass — they determined the amount of spiny matter in the sediment.

What these fossil spines document is that the deep sea has been continuously populated by irregular echinoids since at least the Early Cretaceous period, about 104 million years ago. It offers more exciting insights into the past: the devastating meteorite impact at the end of the Cretaceous period about 66 million years ago, which led to a worldwide mass extinction – with dinosaurs being the most prominent victims – and also caused major disruptions to wildlife. deep sea

This is demonstrated by the morphological changes in the spines: they were thinner and less varied in shape after the event than they were before. Researchers interpret this as the “Lilliput effect.” This means that smaller species have a survival advantage after mass extinctions, resulting in a species having a smaller body size. Perhaps the reason was the lack of food at the bottom of the deep sea.

“We interpret the changes in the spines as an indicator of ongoing evolution and the emergence of new species in the deep sea,” explains Dr. Frank Weise from the Department of Geobiology at the University of Göttingen, lead author of the study. He confirms another discovery: “About 70 million years ago, the biomass of sea urchins increased. We know that water cools down at the same time. This relationship between deep-sea biomass and water temperature allows us to speculate about how the deep sea will change due to human-caused global warming.

Reference: “The 104-million-year record of deep-sea atelostomata (Holsteroda, Spatanguida, Echinacea irregularis) – a story of persistence, food availability and the Big Bang” by Frank Wiese, Nils Schlüter, Jessica Zirkle, and Jens O. Herle, Oliver Friedrich, August 9, 2023, Plus one.
doi: 10.1371/journal.pone.0288046

In addition to the University of Göttingen, the universities of Heidelberg and Frankfurt as well as the Nature Museum in Berlin participated in the research project.

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