104-million-year-old fossils reveal the ocean’s past

Scientists have found fossil evidence that higher invertebrates, particularly irregular echinoids, or sea urchins, have consistently colonized the deep sea for at least 104 million years since the Cretaceous period. Analyzing more than 40,000 vertebrate fragments from sediment samples, the team found evolutionary changes over time, particularly after major extinction events, and suggested potential impacts of future global warming on deep-sea ecosystems.

A team led by the University of Göttingen described the first occurrence of irregular sea urchins in the deep oceans.

Within the abyss of the ocean, our planet’s earliest and most basic life forms are believed to have formed eons ago. Nowadays, the deep sea is known for its exotic fauna. Researchers are investigating how species The diversity of the seabed has evolved over time.

Deep-sea ecosystems are hypothesized to have been reborn repeatedly following multiple mass extinctions and ocean disturbances. Therefore, current marine life at these depths may be relatively recent in Earth’s chronology. However, growing evidence indicates that parts of this underwater realm may be older than once thought.

A research team led by the University of Göttingen has now provided the first fossil evidence for permanent colonization of a deep-sea platform. Invertebrates For at least 104 million years. Fossil vertebrae of irregular echinoids (sea urchins) indicate their long existence. Cretaceous period, as well as their evolution under the influence of fluctuating environmental conditions. The results are published in the journal PLOS ONE.

A sequence of sea urchin vertebrae from different periods of Earth's history illustrates the diversity of forms

Illustrates the different shapes of sea urchin vertebrae from different periods of Earth’s history. Credit: PLOS ONE, 2023 Wiese et al.

The researchers analyzed more than 1,400 sediment samples from boreholes ranging in depth from 200 to 4,700 meters in the Pacific, Atlantic and Southern Oceans. They discovered more than 40,000 vertebrates, which were assigned to a group called irregular echinoids based on their structure and shape.

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

What these fossilized vertebrates document is that the deep sea has been continuously populated by irregular echinoids since at least the Early Cretaceous period, 104 million years ago. And they offer even more fascinating insights into the past: a catastrophic meteorite impact at the end of the Cretaceous period, about 66 million years ago, that led to a global mass extinction – with dinosaurs as the most prominent victim – caused considerable disruption. deep sea

This is shown by the morphological changes in the spines: they were thinner and less varied in shape after the event than before. The researchers explain this as the „Lilliput effect”. This means that smaller species have a survival advantage after a mass extinction, leading to a smaller body size of an organism. There may have been food shortages at the bottom of the deep sea.

„We interpret the changes in the vertebrates as a sign of the constant evolution and emergence of new species in the deep sea,” explains Dr. Frank Weiss from the Department of Geology at the University of Göttingen, lead author of the study. He emphasizes another finding: “About 70 million years ago, the biomass of sea urchins increased. At the same time we know that the water cooled. This relationship between deep-sea biomass and water temperature allows us to infer how the deep sea will change due to human-induced global warming.

Note: „A 104-Ma record of Atelostomata (Holasterioda, Spatangoida, irregular echinoids) in the deep sea – a story of persistence, food availability and a big explosion” by Frank Weiss, Nils Schlueter, Jessica Zirkel, Jens O. Herl and Oliver Friedrich, 9 August 2023, PLOS ONE.
DOI: 10.1371/journal.pone.0288046

In addition to the University of Göttingen, the Universities of Heidelberg and Frankfurt and the Museum für Naderkunde Berlin were involved in the research project.

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