Fossil spines reveal deep-sea past

At the bottom of the deep sea, the first very simple forms of life may have appeared on Earth long ago. Today, the deep sea is famous for its exotic animals. Extensive research is being done on how the number of species living on the sea floor has changed in the meantime.

Some theories say that deep-sea ecosystems emerged again and again after multiple mass extinctions and oceanic disturbances. Thus life today in the deep sea would be relatively recent in Earth’s history. But there is growing evidence that parts of this world are much older than previously thought.

A research team led by the University of Göttingen has provided the first fossil evidence of a stable colonization of the deep sea floor by higher invertebrates for at least 104 million years. Spiny fossils of irregularly shaped sea urchins (sea urchins) indicate their long existence since the Cretaceous period, as well as their evolution under the influence of fluctuating environmental conditions. The results have been published in the journal Plus one.

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 spines, which they assigned 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 quantified the amount of spiny matter in the sediment.

What these fossil spines document is that the deep sea has been continuously inhabited by irregular urchins since at least the early Cretaceous period, about 104 million years ago. And they offer even more exciting insights into the past: the devastating meteorite impact at the end of the Cretaceous period some 66 million years ago, which led to mass extinction around the world – with the dinosaurs being the main victims – and caused major disruptions to wildlife. deep sea

This is shown by the morphological changes in the spines: they were thinner and less varied in shape after the event than they were before. Researchers explain this as the “Lilliput effect.” This means that smaller species have the advantage of surviving mass extinctions, which results in smaller body sizes. Perhaps the reason was the lack of food at the bottom of the deep sea.

“We interpret changes in spines as an indication of continued evolution and emergence of new species in the deep sea,” explains Dr. Frank Wiese 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 the water cooled at the same time. This relationship between deep sea biomass and water temperature allows us to speculate on how the deep sea cooled.” It will change due to human-caused global warming.”

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