An old armored sea monster

THis former armored sea monster snatched his marine prey with a great bite over 300 million years ago. Belonging to the ferocious Dunkleosteus Like, he was one of the first apex predators on the planet. Such formidable creatures, as well as swarms of aquatic life, could not have evolved without the arrival of oxygen in deep environments, suggests recent research. The new document, published in the Proceedings of the National Academy of Sciences, Supports the hypothesis that the availability of oxygen has propelled the evolution of a dynamic mixture of marine life.

Previously, the researchers have speculated This oxygen reached the deep ocean in a single blow, about 540 million years ago. But new studies have suggested a more progressive infiltration of oxygen occurring at several stages, which has potentially started with oxygen that infiltrates near the coast and finally dive into lower depths.

After the first old point of oxygen, the levels of the deep ocean have decreased considerably compared to the following minennia, proposes the new study. About 390 million years ago, about 390 million years ago that enough oxygen to support robust biological networks returned to these depths. This time, oxygen was there to stay.

This transition to sustained and higher levels of oxygen in deep ocean waters aligned with the emergence of a kaleidoscope of marine animals, an event nicknamed “the medium-paleozoic marine revolution”. These included jaw fish like Dunkleosteus, the former parents of the majority of modern vertebrates. The abundant oxygen supply, which researchers attribute to the increasing abundance of woody plants on earth, may have even allowed marine animal species to swell.

This calendar comes from a meticulous analysis of the sedimentary rocks which arose on the edges of the continents from 252 to 541 million years. By inspecting the report of various isotopes of the element Selenium in the layers of these rocks, the researchers identified the specific periods when oxygen was abundant enough for animals to thrive.

“This study gives a strong vote according to which oxygen dictated the moment of the evolution of early animals, at least for the appearance of vertebrates in the jaw in the habitats of the deep ocean,” said study author Michael Kipp, geochemist at Duke University, in a press release.

These results are also important for today’s marine animals. The runoff of the nutrients induced by the man of the land has nourished the increasingly aggressive phytoplankton flowers in the waters of the world, which can sap oxygen areas while the booming populations die and decompose. “It was a balance about 400 million years ago, and it would be a shame to disturb it today in a few decades,” said Kipp.

Main illustration of Nobu Tamura

• Molly Glick

  Published on August 27, 2025

  Molly Glick is the editor of the newsletter of Nautilus.