Did This Spiral Sea Creature Outlive the Dinosaurs?

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AAbout 66 million years ago, tragedy struck the dinosaurs when a massive space rock fell on what is now the Yucatán Peninsula in southeastern Mexico. This killed about 75 percent of all species on the planet, including dinosaurs.

Scientists have long thought that ammonites – extinct, curly-shelled molluscs related to today’s squid and octopuses – perished in this catastrophe, known as the Cretaceous-Paleogene extinction event. Some teams had previously proposed that some ammonites survived, based on fossil discoveries, but this theory proved controversial.

Today, evidence suggests that some of these spiral-shaped species eventually managed to persist. A recent analysis of ammonite fossils discovered around a coastal cliff in Denmark, a site known as Stevns Klint, suggests that these cephalopods crossed the sea after the mass extinction.

This site contains a well-defined rock layer full of fossils that represents the boundary between the Cretaceous and Paleogene periods. A team of scientists from Europe and the United States inspected ammonite fossils from the first piece of the Paleogene section of the site, which has previously been studied for information on creatures that recovered from the asteroid impact in shallow marine environments.

These ammonite remains were previously thought to date back to before the extinction, eroding and landing in a newer rock layer. But according to microscopic analysis of these controversial fossils, the mud they contained contained tiny sponge tips commonly found in remains from the early Paleogene period. They also couldn’t find evidence of tiny moss animals or sea mats typically associated with the Cretaceous period, according to a recently published paper in Scientific reports.

Read more: »The origin of the asteroid that killed the dinosaurs»

The microscopic evidence agrees with past estimates that the ammonites remained nearly 70,000 years after the asteroid impact. This means that the case of the ammonites still remains to be solved – future studies should aim to determine “what actually killed the last ammonites that lived on Earth,” the authors write.

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Main image: Stefano Puzzuoli / Wikimedia Commons

• Molly Glick

  Published on January 7, 2026

  Molly Glick is the newsletter editor of Nautilus.